Biomass burning in the tropics: impact on atmospheric chemistry and biogeochemical cycles

Kinetic nitrogen isotope effects of 18 amino acids degradation during burning processes

Understanding the nitrogen isotopic variations of individual amino acids (AAs) is essential for utilizing the nitrogen isotope values of individual amino acids (δ15N-AA) as source indicators to identify proteinaceous matter originating from biomass combustion processes. However, the nitrogen isotope effects (ε) associated with the degradation of individual amino acids during combustion processes have not been previously explored. In this study, we measured the nitrogen isotope values of residual free amino acids -following a series of controlled combustion experiments at temperatures of 160-240 °C and durations of 2 min to 8 h, as described in Part 1. δ15N values of proline, aspartate, alanine, valine, glycine, leucine, and isoleucine are more positive than their initial δ15N values after prolonged combustion. Variations in δ15N values of the most AAs conform to the Rayleigh fractionation during combustion and their nitrogen isotope effects (ε) are greatly impacted by their respective combustion degradation pathways. This is the first time the ε values associated with the degradation pathways of AAs during combustion have been characterized. Only the ε values associated with Pathway 1 (dehydration to form dipeptide) and 2 (simultaneous deamination and decarboxylation) are found to be significant and temperature-dependent, ranging from + 2.9 to 6.4‰ and + 0.9‰ to + 3.8‰, respectively. Conversely, ε values associated with other pathways are minor. This improves the current understanding on the degradation mechanisms of protein nitrogen during biomass burning.

Aerosolomics based approach to discover source molecular markers: A case study for discriminating residential wood heating vs garden green waste burning emission sources

Biomass burning is a significant source of particulate matter (PM) in ambient air and its accurate source apportionment is a major concern for air quality. The discrimination between residential wood heating (RWH) and garden green waste burning (GWB) particulate matter (PM) is rarely achieved. The objective of this work was to evaluate the potential of non-targeted screening (NTS) analyses using HRMS (high resolution mass spectrometry) data to reveal discriminating potential molecular markers of both sources. Two residential wood combustion appliances (wood log stove and fireplace) were tested under different output conditions and wood moisture content. GWB experiments were carried out using two burning materials (fallen leaves and hedge trimming). PM samples were characterized using NTS approaches with both LC- and GC-HRMS (liquid and gas chromatography-HRMS). The analytical procedures were optimized to detect as many species as possible. Chemical fingerprints obtained were compared combining several multivariate statistical analyses (PCA, HCA and PLS-DA). Results showed a strong impact of the fuel nature and the combustion quality on the chemical fingerprints. 31 and 4 possible markers were discovered as characteristic of GWB and RWH, respectively. Complementary work was attempted to identify potential molecular formulas of the different potential marker candidates. The combination of HRMS NTS chemical characterization with multivariate statistical analyses shows promise for uncovering organic aerosol fingerprinting and discovering potential PM source markers.

Revisiting regional and seasonal variations in decadal carbon monoxide variability: Global reversal of growth rate

Carbon monoxide (CO) is one of the important trace gases in the atmosphere capturing the evolution of chemical properties of the troposphere. Here we analyze the growth rates of CO during the period of 1991-2020 using in situ measurements from the World Meteorological Organization's (WMO) Global Atmospheric Watch (GAW) program. The analysis of trends has been done on different spatial and temporal scales. Our analysis supports the decline in the overall CO mixing ratios over the globe but inter-decadal and regional trend analysis has shown heterogeneous changes in the given period of study. On average, there has been a decrease of -16.22 ± 1.92 ppb and -4.5 ± 0.64 ppb observed at the sites in the northern hemisphere (NH) and southern hemisphere (SH), respectively. This decline occurred at rates of -0.80 ± 0.12 ppb yr-1 in the NH and - 0.12 ± 0.03 ppb yr-1 in the SH. Bifurcating the annual trends for seasonal analysis reveals the impact of emissions, chemistry and atmospheric transport on CO variation over different regional clusters of stations. Seasonal trend analysis provides further evidence regarding heterogeneous patterns in the South-East Asia region. Our study highlights a slowdown in CO decline during the 2011-2020 decade when compared to the rate of decrease observed in 2001-2010. This is inferred from the variability and much slower decline of CO emissions across different regions, contributing to a weakening in CO trends.

Hydrocarbon markers for assessing the influence of human activities in the tropical semi-arid region (Acaraú River, state of Ceará, Brazil)

Coastal ecosystems are facing increasing anthropogenic stressors, including rapid urbanization rates and extensive fossil fuel usage. Nevertheless, the distribution of hydrocarbons in the Brazilian semi-arid region remains relatively uncharacterized. In this study, we analyzed ten surface sediment samples (0-2 cm) along the banks of the Acaraú River to assess the chronic contributions of aliphatic and aromatic hydrocarbons. The Acaraú River is a crucial riverine-estuarine area in the semi-arid region of Northeast Brazil. Ultrasound-assisted extraction and gas chromatograph coupled to a mass spectrometer were used to identify target compounds: 45 PAHs, 27 n-alkanes (C10-C38), and two isoprenoids. At most stations, the predominant grain size was sand, and the organic carbon content was less than 1%. The total n-alkanes concentration ranged from 14.1 to 170.0 μg g-1, while individual pristane and phytane concentrations ranged from not detected (nd) to 0.4 μg g-1 and nd to 0.7 μg g-1, respectively. These concentrations resemble those found in unpolluted sediments and are lower compared to samples from urbanized coastal areas. The total USEPA PAHs concentration varied from 157.8 to 1364 ng g-1, leading to the characterization of sediment samples as moderately polluted. Based on diagnostic ratios calculated from both alkane and PAH concentrations, the sediment samples were predominantly deriving from pyrolytic sources, with some contribution from petrogenic sources. The most abundant group was 5-ring PAHs (mean: 47.3 ± 36.7%), followed by 3-ring PAHs (mean: 17.9 ± 13.7%). This predominance indicates a pyrolytic origin of hydrocarbons in the Acaraú River. The concentrations reported here were representative of the level of background hydrocarbons in the region. Regarding the sediment quality assessment, BaP TPE calculated for the Acaraú River ranged from 13.2 to 1258.4 ng g-1 (mean: 409.3 ± 409.4 ng g-1). When considering site-specific sediment quality values for the coast of the state of Ceará, half of the stations are classified as strongly contaminated, and toxic effects are expected to occur (SQGq >0.25) for the ∑16 PAHs measured in the samples, especially due to dibenz [a,h]anthracene concentrations.

Spatiotemporal distribution of air pollutants during a heat wave-induced forest fire event in Uttarakhand

Prevailing dry conditions and rainfall deficit during the spring season in North India led to heat wave conditions which resulted in widespread and intense forest fire events in the Himalayan state of Uttarakhand during April 16-30, 2022. A total of 7589 active fires were detected by VIIRS during the second half of April 2022 compared to 1558 during the first half. The TROPOMI observed total column values of CO and NO2 increased by 4.4% and 11.7%, respectively during April 16-30, 2022 with respect to April 1-15, 2022. A noticeable increase in surface level concentration of trace gases was also observed at Dehradun. In situ measurements of CO, NOx, and O3 during April 16-30, 2022 show an increase of 133, 35, and 6% compared to previous year observations during the same period. Weather Research and Forecasting model with chemistry (WRF-Chem) is utilized to quantitatively estimate the contribution of this event on the distribution of air pollutants over this state. The model results were evaluated against ERA5 reanalysis, upper air soundings, and TROPOMI-retrieved total column density (TCD) of CO, NO2, and O3. Two simulations with (Fire) and without (NoFire) biomass burning emissions input were performed to quantify the contribution of forest fires to the concentration of trace gases and particulates. The CO, NO2, and O3 emitted/produced from forest fire over Uttarakhand during April 2022 contributed approximately 39.95, 35.73, and 9.97% to the surface concentration of respective gas. In the case of aerosols, it was around 71.20, 71.44, and 33.62% for PM2.5, PM10, and BC respectively. The vertical profile analysis of pollutants revealed that extreme forest fire events can perturb the distribution of air pollutants from the surface up to 450 hPa.

Space-Based Observations of Ozone Precursors within California Wildfire Plumes and the Impacts on Ozone-NOx-VOC Chemistry

The frequency of wildfires in the western United States has escalated in recent decades. Here we examine the impacts of wildfires on ground-level ozone (O3) precursors and the O3-NOx-VOC chemistry from the source to downwind urban areas. We use satellite retrievals of nitrogen dioxide (NO2) and formaldehyde (HCHO, an indicator of VOC) from the Tropospheric Monitoring Instrument (TROPOMI) to track the evolution of O3 precursors from wildfires over California from 2018 to 2020. We improved these satellite retrievals by updating the a priori profiles and explicitly accounting for the effects of smoke aerosols. TROPOMI observations reveal that the extensive and intense fire smoke in 2020 led to an overall increase in statewide annual average HCHO and NO2 columns by 16% and 9%. The increase in the level of NO2 offsets the anthropogenic NOx emission reduction from the COVID-19 lockdown. The enhancement of NO2 within fire plumes is concentrated near the regions actively burning, whereas the enhancement of HCHO is far-reaching, extending from the source regions to urban areas downwind due to the secondary production of HCHO from longer-lived VOCs such as ethene. Consequently, a larger increase in NOx occurs in NOx-limited source regions, while a greater increase in HCHO occurs in VOC-limited urban areas, both contributing to more efficient O3 production.

A spatio-temporal analysis of fire occurrence patterns in the Brazilian Amazon

Wildfires in the Amazon significantly impact the forest structure and carbon cycle. Understanding the patterns of fire occurrence is crucial for effective management. A novel spatio-temporal point process framework was used to analyze changes in fire occurrence patterns in the Brazilian Amazon. A dynamic representation of a Log Gaussian Cox process was used to model the intensity function, which was decomposed into trend, seasonality, cycles, covariates, and spatial effects. The results show a marked decrease in long-term fire occurrence movements between the start of the sample and 2012, followed by an increase until the end of the sample, attributed to governance measures and market mechanisms. Spatial variability of fire occurrence rates in the Brazilian Amazon was successfully captured, with regions having more dry seasons experiencing higher fire occurrence rates. This analysis provides valuable insights into fire occurrence patterns in the Amazon region and the factors driving them.

Hybrid Targeted/Untargeted Screening Method for the Determination of Wildfire and Water-Soluble Organic Tracers in Ice Cores and Snow

Wildfires can influence the earth's radiative forcing through the emission of biomass-burning aerosols. To better constrain the impacts of wildfires on climate and understand their evolution under future climate scenarios, reconstructing their chemical nature, assessing their past variability, and evaluating their influence on the atmospheric composition are essential. Ice cores are unique to perform such reconstructions representing archives not only of past biomass-burning events but also of concurrent climate and environmental changes. Here, we present a novel methodology for the quantification of five biomass-burning proxies (syringic acid, vanillic acid, vanillin, syringaldehyde, and p-hydroxybenzoic acid) and one biogenic emission proxy (pinic acid) using solid phase extraction (SPE) and ultrahigh-performance liquid chromatography coupled with high-resolution mass spectrometry. This method was also optimized for untargeted screening analysis to gain a broader knowledge about the chemical composition of organic aerosols in ice and snow samples. The method provides low detection limits (0.003-0.012 ng g^-1), high recoveries (74 ± 10%), and excellent reproducibility, allowing the quantification of the six proxies and the identification of 313 different molecules, mainly constituted by carbon, hydrogen, and oxygen. The effectiveness of two different sample storage strategies, i.e., re-freezing of previously molten ice samples and freezing of previously loaded SPE cartridges, was also assessed, showing that the latter approach provides more reproducible results.

Perspective on Particulate Matter: From Biomass Burning to the Health Crisis in Mainland Southeast Asia

Air pollution, notably particulate matter pollution, has become a serious concern in Southeast Asia in recent decades. The combustion of biomass has been recognized to considerably increase air pollution problems from particulate matter in this region. Consequently, its effect on people in this area is significant. This article presents a synthesis of several datasets obtained from satellites, global emissions, global reanalysis, and the global burden of disease (GBD) to highlight the air quality issue and emphasize the health crisis in mainland Southeast Asia. We found that the death rates of people have increased significantly along with the rise of hotspots in mainland Southeast Asia over the last two decades (2000-2019). In comparison, most countries saw a considerable increase in the predicted fatality rates associated with chronic respiratory illnesses during those two decades. Several reports highlight the continued prevalence of chronic respiratory diseases likely related to poor air quality in Southeast Asia.

County-level and monthly resolution multi-pollutant emission inventory for residential solid fuel burning in Fenwei Plain, China

The Fenwei Plain (FWP) in central China is the fourth largest plain nationwide. This region has experienced severe air pollution during the past decades, largely due to residential solid fuel burning. A regional-scale emission inventory covering multi-pollutants was currently unavailable for this area due to the lack of localized emission factors (EFs) from various sources. In this study, localized EFs derived from previous in situ measurements and detailed county-level activity data were used to develop an emission inventory of particulate and gaseous pollutants for the source sector of five residential solid fuels in the FWP in 2020. Emissions of particulate matter with an aerodynamic diameter of ≤2.5 μm (PM_2.5), organic carbon (OC), elemental carbon (EC), ions, polycyclic aromatic hydrocarbons (PAHs), carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO₂), and volatile organic compounds (VOCs) were estimated to be 230-290, 89-160, 20-29, 31-54, 0.93-22, 2100-3600, 64-87, 9.3-12, and 45-92 Gg/yr, respectively. The county-level distribution characteristics differed between pollutant species due to their different EFs and consumption patterns of solid fuels. Shouyang County emitted most for all pollutants (2.66%-4.91% of the region total) except PM_2.5 and SO₂, for which Xiangfen and Hongtong County emitted the most (2.64% and 2.90%), respectively. Emissions were higher in cold (SO₂ during November to January, other pollutants during November to February) than warm months. Uncertainties in this newly developed emission inventory were estimated to be 25.2%-69.8%, much lower than those of existing ones, demonstrating the reliability of this inventory. Gini coefficients indicated that EC, PAHs, NOx, and VOC emissions exhibited evident regional disparities, e.g., Yuncheng and Jinzhong had high pollution levels despite low economic output. Future emission control policies should first focus on developing regions with high pollution in FWP.

A synthesis of mercury research in the Southern Hemisphere, part 2: Anthropogenic perturbations

Environmental mercury (Hg) contamination is a global concern requiring action at national scales. Scientific understanding and regulatory policies are underpinned by global extrapolation of Northern Hemisphere Hg data, despite historical, political, and socioeconomic differences between the hemispheres that impact Hg sources and sinks. In this paper, we explore the primary anthropogenic perturbations to Hg emission and mobilization processes that differ between hemispheres and synthesize current understanding of the implications for Hg cycling. In the Southern Hemisphere (SH), lower historical production of Hg and other metals implies lower present-day legacy emissions, but the extent of the difference remains uncertain. More use of fire and higher deforestation rates drive re-mobilization of terrestrial Hg, while also removing vegetation that would otherwise provide a sink for atmospheric Hg. Prevalent Hg use in artisanal and small-scale gold mining is a dominant source of Hg inputs to the environment in tropical regions. Meanwhile, coal-fired power stations continue to be a significant Hg emission source and industrial production of non-ferrous metals is a large and growing contributor. Major uncertainties remain, hindering scientific understanding and effective policy formulation, and we argue for an urgent need to prioritize research activities in under-sampled regions of the SH.

Characterization of paddy-residue burning derived carbonaceous aerosols using dual carbon isotopes

A large scale paddy-residue burning (PRB) happens every year in the northwest Indo-Gangetic Plain (IGP) during the post-monsoon season, and winds transport pollutants from the source region up to the northern Indian Ocean affecting air quality of the IGP and marine region. In this study, day-night pairs of fine aerosol samples (n = 69) were collected during October-November over Patiala (30.2°N, 76.3°E, 250 m amsl), a site located in the source region of PRB. Carbonaceous aerosols (CA) were characterised using chemical species and dual carbon isotopes (¹³C and ¹⁴C) to estimate bio vs non-bio contributions and understand their characteristics. Percentage of bio fraction (f_bio, estimated using ¹⁴C) in CA varied from 74 % to 87 % (avg: 80 ± 3) during days and 71 % to 96 % (avg: 85 ± 7 %) during nights. Further, the f_bio was found to be better correlated with aerosol mass spectrometer derived f60 compare to levoglucosan (LG) or nssK⁺, suggesting f60 a useful proxy for PRB. The δ¹³C varied from -27.7 ‰ to -26.0 ‰ (avg: -27.0 ± 0.4 ‰) and - 28.7 ‰ to -26.4 ‰ (avg: -27.5 ± 0.7 ‰) during day and night, respectively. Measured δ¹³C of the samples was found to be more enriched than expected by 0.3 to 2.0 ‰, indicating the presence of aged CA also in Patiala even during PRB period. From f_bio versus δ¹³C correlation, and from Miller-Trans plot, δ¹³C of PRB is found to be -28.9 ± 1.1 ‰, which also infers that Miller-Trans plot can be used to understand source isotopic signature in the absence of radiocarbon measurements in aerosols. Further, the characteristics ratios of organic carbon (OC) to elemental carbon (EC) (11.9 ± 4.1), LG to potassium (K⁺) (0.84 ± 0.15), OC/LG (19.7 ± 2.0) and K⁺/EC (0.75 ± 0.27) were calculated by considering samples with f_bio higher than 0.90, which can be used for source apportionment studies. Such studies are crucial in assessing the effects of PRB on regional air quality and climate.

Impact of satellite AOD data on top-down estimation of biomass burning particulate matter emission

Particulate matter emitted from open biomass burning affects climate, air quality and public health. In the development of remote sensing techniques, top-down methods using satellite observations have become an effective way to estimate particulate matter emissions, but different spatial resolution and coverage of satellite aerosol optical depth (AOD) products introduce great uncertainties. In this work, we assess the differences in total particulate matter (TPM) emission when calculated using different satellite AOD data. To do this, we derive top-down biomass burning TPM emission coefficients (Ce) of Australia based on 1 km and 10 km MODIS AOD products, and compare the results of emission estimation. Using high spatial resolution AOD data, a 90 % decrease of Ce mean value is found in Australia, and the quality of Ce improves by 290 %. When we use 1 km AOD data in place of 10 km AOD data, the estimation of biomass burning TPM emissions in Australia during 2012-2020 drops from 1.08Tg to 0.11Tg; the temporal trends of the two products remain the same. The TPM emission estimates for biome based on higher spatial resolution AOD data in this study are lower than Fire Energetics and Emissions Research (FEERv1) inventories by factors of 0.08-0.2. Our work shows that using satellite AOD products of higher spatial resolution avoids overestimation of biomass burning TPM emissions, and improves the quality of final estimates, providing a possible way to understand biomass burning emission more accurately.

Mapping the Contribution of Biomass Burning to Persistent Organic Pollutants in the Air of the Indo-China Peninsula Based on a Passive Air Monitoring Network

Biomass burning (BB) is an important source of atmospheric persistent organic pollutants (POPs) across the world. However, there are few field-based regional studies regarding the POPs released from BB. Due to the current limitations of emission factors and satellites, the contribution of BB to airborne POPs is still not well understood. In this study, with the simultaneous monitoring of BB biomarkers and POPs based on polyurethane foam-based passive air sampling technique, we mapped the contribution of BB to polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in the Indo-China Peninsula. Spearman correlations between levoglucosan and 16 PCBs (r_s = 0.264-0.767, p < 0.05) and 2 OCPs (r_s = 0.250-0.328, p < 0.05) confirmed that BB may facilitate POP emissions. Source apportionment indicated that BB contributed 9.3% to the total PCB and OCP mass. The high contribution of positive matrix factorization-resolved BB to PCBs and OCPs was almost consistent with their concentration distributions in the open BB season but not completely consistent with those in the pre-monsoon and/or monsoon seasons. Their contribution distributions may reflect the use history and geographic distribution in secondary sources of POPs. The field-based contribution dataset of BB to POPs is significant in improving regional BB emission inventories and model prediction.

Classification of MODIS fire emission data based on aerosol absorption Angstrom exponent retrieved from AERONET data

Biomass burning emits a large quantity of gaseous pollutants and aerosols into the atmosphere, which perturbs the regional and global climate and has significant impacts on air quality and human health. In order to understand the temporal and spatial distributions of biomass burning and its contribution to aerosol optical and radiative impacts, we examined fire emission data and its contribution to aerosol optical and radiative impacts over six major hot-spot continents/sub-continents across the globe, namely North-Central (NC) Africa, South America, US-Hawaii, South Asia, South East Asia, and Australia-New Zealand, using long-term satellites, ground-based and re-analysis data during 2000-2021. The selected six sites contributed ∼70% of total global fire data. The classification of biomass burning, such as pre, active, and post burning phases, was performed based on the Absorption Angstrom Exponent (AAE) estimated from 55 AERONET (AErosol RObotic NETwork) stations. The study found the highest contribution of fire count (55 %) during the active burning phase followed by post (36 %) and pre (8 %) burning phases. Such high fire counts were associated with high absorption aerosol optical depth (AAOD) during the active fire event. Strong dominance of fine and coarse mode mixed aerosols were also observed during active and post fire regimes. High AAOD and low Extinction Angstrom Exponent (EAE) over NC Africa during the fire events suggested presence of mineral dust mixed with biomass burning aerosols. Brightness temperature, fire radiative power and fire count were also dominated by the active burning followed by post and pre burning phases. The maximum heating rate of 3.15 K day^-1 was observed during the active fire events. The heating rate profile shows clear variations for three different fire regimes with the highest value of 1.80 K day^-1 at ∼750 hPa altitude during the active fire event.

Spatiotemporal characteristics of air pollution in Chengdu-Chongqing urban agglomeration (CCUA) in Southwest, China: 2015-2021

Studying the spatiotemporal characteristics of air pollutants in urban agglomerations and their response factors will help to improve the quality of urban living. In combining air quality monitoring data and wavelet analysis from the Chengdu-Chongqing urban agglomeration (CCUA), this study assessed the spatiotemporal distribution characteristics and influential factors of air pollutants on daily, monthly and annual scales. The results showed that the concentration of air pollutants in the CCUA has decreased year by year, and air quality has improved. Except for O₃, pollutants in autumn and winter were higher than those in summer. The spatial distribution of air pollutants was obvious distributed in Chengdu, Chongqing, Zigong and Dazhou. Pollution incidents were mainly concentrated in winter. The 6 air pollutants and air quality index (AQI) have dominant periods on multiple time scales. AQI showed positive coherence with PM_2.5 and PM₁₀ on multiple time scales, and obvious positive coherence with SO₂, CO, NO₂ and O₃ in the short term scale. AQI was not strongly correlated with the fire point, but exhibited obvious negative coherence in the long term scale. In addition, AQI showed an obvious positive correlation with temperature and sunshine hours in short term, and a clear negative correlation with humidity and rainfall. The research results of this paper will provide a reference for pollution prevention and control in the CCUA.

Quantifying international and interstate contributions to primary ambient PM2.5 and PM10 in a complex metropolitan atmosphere

We quantify the contributions of long-range and regionally transported aerosols to ambient primary PM_2.5 and PM₁₀ in a representative United States industrialized/urban atmosphere via detailed elemental analysis and chemical mass balance (CMB) modeling after identifying their presence using a variety of publicly available satellite data/information, software products, and synoptic-scale aerosol models. A year-long study in Houston, Texas identified North African dust as the principal long-range global source of primary particulate matter (PM). CMB estimated transatlantic dust from the Sahara-Sahel region to be dominant in the summer months contributing an average of 3.5 μg m^-3 to PM_2.5 and 7.9 μg m^-3 to PM₁₀ during May-August, i.e., the active Saharan dust season. Biomass burning was the chief source of regionally transported PM impacting air quality on different occasions throughout the year depending on the fire location. Four major biomass combustion events affecting air quality in Texas were calculated to contribute an average of 1.3 μg m^-3 to PM_2.5 and 1.4 μg m^-3 to PM₁₀ in corresponding samples whose origins were tracked to Canada, southeastern states of USA, and Central America using fire maps, HYSPLIT back trajectories, and the Navy Aerosol Analysis and Prediction System global aerosol model. Elemental concentrations and signature ratios revealed significant mixing of potassium, rare earth metals, and vanadium from proximal and distal crustal (natural) sources with anthropogenically emitted PM. This demonstrates the need to isolate the non-mineral components of these metals to employ them as tracers for primary PM emitted by biomass burning, petroleum refineries, and oil combustion. Transboundary contributions to primary PM_2.5 were 1.5 μg m^-3 and 3.1 μg m^-3 to PM₁₀ adding 16% to annual average mass concentration of both size fractions demonstrating that local sources were primarily responsible for ambient air quality with non-trivial contributions from international and interstate sources. Rigorously identifying and quantifying aerosol sources assists in improving air quality management policies designed to protect public health and comply with ever-decreasing federal PM standards that allow state agencies to exclude contributions that are not reasonably controllable or preventable from regulatory decisions and actions.

Integrated assessment of volatile organic compounds from industrial biomass boilers in China: emission characteristics, influencing factors, and ozone formation potential

Industrial biomass boilers (IBBs) are widely promoted in China as a type of clean energy. However, they emit large amount of volatile organic compounds (VOCs) and the emission characteristics and the underlying factors are largely unknown due to the sampling difficulties. In this study, three wood pellet-fueled and two wood residue-fueled IBBs were selected to investigate the characteristics of VOC emissions and to discover their underlying impacting factors. The emission factor of VOCs varied from 21.6 ± 2.8 mg/kg to 286.2 ± 10.8 mg/kg for the IBBs. Oxygenated VOCs (OVOCs) were the largest group, contributing to 30.3 - 73.6% of the VOC emissions. Significant differences were revealed in the VOC source profiles between wood pellet-fueled and wood residue-fueled IBBs. Operating load, excess air, furnace temperature, and fuel type were identified as the primary factors influencing VOC emissions. The excess air coefficient should be limited below 3.5, roughly corresponding to the operating load of 62% and furnace temperature of 630 °C, to effectively reduce VOC emissions. VOC emissions also showed great differences in different combustion phases, with the ignition phase having much greater VOC emissions than the stable combustion and the ember phases. The ozone formation potential (OFP) ranged from 4.3 to 31.2 mg/m³ for the IBBs, and the wood residue-fueled IBBs yielded higher OFP than the wood pellet-fueled ones. This study underscored the importance of OVOCs in IBB emissions, and reducing OVOC emissions should be prioritized in formulating control measures to mitigate their impacts on the atmospheric environment and human health.

Spatial distribution and temporal variation of biomass burning and surface black carbon concentrations during summer (2015‒2021) in India

Historical biomass burning in summer season (April‒June, during 2015‒2021) was assessed by studying active fire spot data recorded by the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard NASA/NOAA Suomi NPP satellite and mapping the same over Indian landmass. The fire spots often formed regional clusters and most profusely covered the states of Odisha, Chhattisgarh, Andhra Pradesh, Telengana, Madhya Pradesh, Maharashtra, Jharkhand, Karnataka, Punjab, Uttar Pradesh, Haryana, Gujarat, Tamil Nadu, Manipur, Nagaland, and Mizoram during April but their number decreased conspicuously in May and further in June. Forward movements of air masses potentially carrying fire-induced air pollutants from five principal fire cluster regions (northern, south eastern, western, north-eastern, and central) of India during April and May in 2021 were traced by 6-day forward airtrajectory modelling. It was observed that many parts of India were the recipients of air coming from the above principal fire clusters. In each year, the surface mass concentration of black carbon (BC), one of the most prominent markers of biomass burning, was higher in April over May and June in the affected regions, commensurate with the most active period of fire. The BC surface mass concentrations progressively declined thereafter in May and June with decreasing number of active fire spots along with declining average monthly height of the planetary boundary layer (PBL), indicating integral connection of surface BC levels with biomass burning. The study suggests that in spite of more favourable meteorological conditions in summer, extensive biomass burning may have had a crucial role to play in perturbing local and regional air quality over India by generating BC and other air pollutants.

Regional monitoring of biomass burning using passive air sampling technique reveals the importance of MODIS unresolved fires

Field-based sampling can provide more accurate evaluation than MODIS in regional biomass burning (BB) emissions given the limitations of MODIS on unresolved fires. Polyurethane foam-based passive air samplers (PUF-PASs) are a promising tool for collecting atmospheric monosaccharides. Here, we deployed PUF-PASs to monitor monosaccharides and other BB-related biomarkers and presented a dataset of 31 atmospheric BB-related biomarkers in the Indo-China Peninsula (ICP) and Southwest China. The peak concentrations of monosaccharides in the ICP occurred before monsoon season. The highest concentrations were in the eastern Mekong plain, while the lowest were along the eastern coast. BB-related biomarkers displayed elevated concentrations after April, particularly in the monsoon season; however, fewer active fires were recorded by MODIS. This revealed the importance of MODIS unresolved fires (e.g., indoor biofuel combustion, small-scale BB incidents, and charcoal fires) to the regional atmosphere. The PAS derived levoglucosan concentrations indicated that, with the inclusion of MODIS unresolved fires, the estimated top-down emissions of PM (4194-4974 Gg/yr), OC (1234-1719 Gg/yr) and EC (52-384 Gg/yr) would be higher than previous bottom-up estimations in the ICP. Future studies on these MODIS unresolved fires and regional monitoring data of BB are vital for improving the modeling of regional BB emissions.

Saccharides in atmospheric PM2.5 in tropical forest region of southwest China: Insights into impacts of biomass burning on organic carbon aerosols

Biomass burning (BB) in South and Southeast Asia has a strong impact on regional air quality, yet its impact on atmospheric PM_2.5 of tropical rainforest regions, a background region occupying a large area in South Asia, has rarely been investigated. In this work, we performed one-year PM_2.5 sampling during December 2018 to October 2019 at a tropical rainforest site in southwest China. PM_2.5 mass concentration, major chemical components, and ten saccharides were determined to study seasonal variations of PM_2.5 chemical composition, and further to understand possible impacts of BB to organic carbon (OC) aerosols at this background region. The concentration levels of PM_2.5, major PM_2.5 components, and total saccharides were significantly higher in dry season than in wet season. Besides, PM_2.5, OC, and total saccharides were highly correlated (R² > 0.64, p < 0.001) during the sampling period, suggesting they might share common sources. Source apportionment of saccharides revealed that BB was the main source in both seasons. Furthermore, the contributions of BB to OC (BB/OC) were estimated using levoglucosan as a molecular tracer while levoglucosan's chemical degradation was considered. It was found that over 80% of LG was degraded in both seasons, suggesting BB sources were largely from the transport of external air mass. The estimated BB/OC were over 50%, indicating BB was an important source of OC and likely of PM_2.5 in both seasons. The air-mass backward trajectory analysis and active fire spots data indicate intense BB emission sources were from South and Southeast Asia in dry season and the BB emissions in southern region of China could impact on the studied area in wet season.

Spatial variations in vegetation fires and emissions in South and Southeast Asia during COVID-19 and pre-pandemic

Vegetation fires are common in South/Southeast Asian (SA/SEA) countries. However, very few studies focused on vegetation fires and the changes during the COVID as compared to pre-pandemic. This study fills an information gap and reports total fire incidences, total burnt area, type of vegetation burnt, and total particulate matter emission variations in SA/SEA during COVID-2020 and pre-pandemic (2012-2019). Results from the short-term 2020-COVID versus 2019-non-COVID year showed a decline in fire counts varying from - 2.88 to 79.43% in S/SEA. The exceptions in South Asia include Afghanistan and Sri Lanka, with a 152% and 4.9% increase, and Cambodia and Myanmar in Southeast Asia, with an 11.1% and 8.5% increase in fire counts in the 2020-COVID year. The burnt area decline for 2020 compared to 2019 varied from - 0.8% to 92% for South/Southeast Asian countries, with most burning in agricultural landscapes than forests. Several patches in S/SEA showed a decrease in fires for the 2020 pandemic year compared to long term 2012-2020 pre-pandemic record, with Z scores greater or less than two denoting statistical significance. However, on a country scale, the results were not statistically significant in both S/SEA, with Z scores ranging from - 0.24 to - 1, although most countries experienced a decrease in fire counts. The associated mean TPM emissions declined from ~ 2.31 Tg (0.73stdev) during 2012-2019 to 2.0 (0.65stdev)Tg in 2020 in South Asia and 6.83 (0.70stdev)Tg during 2012-2019 to 5.71 (0.69 stdev)Tg in 2020 for South East Asian countries. The study highlights variations in fires and emissions useful for fire management and mitigation.

Direct and indirect effects and feedbacks of biomass burning aerosols over Mainland Southeast Asia and South China in springtime

Southeast Asia is one of the largest biomass burning (BB) source regions in the world. In order to promote our understanding of BB aerosol characteristics and environmental impacts, this study investigated the emission, composition, evolution, radiative effects, and feedbacks of BB aerosols from Mainland Southeast Asia during 15 March to 15 April 2019 by using an online-coupled regional chemistry/aerosol-climate model RIEMS-Chem. Model results are compared against a variety of ground and vertical observations, indicating a generally good model performance for meteorology, aerosol chemical compositions, and aerosol optical properties. It is found that BB aerosols contributed significantly to regional particulate matter (PM), accounting for up to 90 % of the near-surface PM_2.5, BC, and OC concentrations over the BB source regions of north Mainland Southeast Asia and for approximately 30-70 % over wide downwind areas including most areas of southwest China and portions of south China. At the top of atmosphere (TOA), BB aerosols exerted a positive all-sky radiative effect (DRE_BB) up to 25 W/m² over north Vietnam and south China, a negative DRE_BB up to -10 W/m² over Myanmar, western Thailand, and southwest China. Meanwhile, the indirect radiative effect (IRE_BB) was consistently negative, with the maximum of -10 W/m² over downwind areas with cloud coverage, e.g., from north Vietnam to most of south China. The subregional (95-125°E and 10-30°N) and period mean DRE_BB and IRE_BB at TOA were estimated to be 0.69 W/m² and - 0.63 W/m², respectively, leading a total radiative effect (TRE_BB) of 0.06 W/m² at TOA. The radiative effects of BB aerosols led to decreases in sensible and latent heat fluxes, near-surface temperature, PBL height, and wind speed of 6.0 Wm^-2, 9.0 Wm^-2, 0.26 °C, 38.7 m, and 0.1 m/s, respectively, accompanied with an increase in RH of 1.9 %, averaged over the subregion and the study period. The accumulated precipitation during the study period was apparently reduced by BB aerosols from east Thailand to south China, with the maximum reduction up to 14 cm (exceeding 40 %) over north Vietnam and south China. TRE_BB tended to increase mean near-surface PM_2.5 and its component concentrations, with the maximum percentage increase up to 24 % over the BB source regions of north Mainland Southeast Asia, resulting from the combined effects of dynamic and chemical feedbacks. DRE_BB generally dominated over IRE_BB in the feedback-induced PM_2.5 concentration changes.

Feedback in tropical forests of the Anthropocene

Tropical forests are complex systems containing myriad interactions and feedbacks with their biotic and abiotic environments, but as the world changes fast, the future of these ecosystems becomes increasingly uncertain. In particular, global stressors may unbalance the feedbacks that stabilize tropical forests, allowing other feedbacks to propel undesired changes in the whole ecosystem. Here, we review the scientific literature across various fields, compiling known interactions of tropical forests with their environment, including the global climate, rainfall, aerosols, fire, soils, fauna, and human activities. We identify 170 individual interactions among 32 elements that we present as a global tropical forest network, including countless feedback loops that may emerge from different combinations of interactions. We illustrate our findings with three cases involving urgent sustainability issues: (1) wildfires in wetlands of South America; (2) forest encroachment in African savanna landscapes; and (3) synergistic threats to the peatland forests of Borneo. Our findings reveal an unexplored world of feedbacks that shape the dynamics of tropical forests. The interactions and feedbacks identified here can guide future qualitative and quantitative research on the complexities of tropical forests, allowing societies to manage the nonlinear responses of these ecosystems in the Anthropocene.

Wild, tamed, and domesticated: Three fire macroregimes for global pyrogeography in the Anthropocene

Climate and natural vegetation dynamics are key drivers of global vegetation fire, but anthropogenic burning now prevails over vast areas of the planet. Fire regime classification and mapping may contribute towards improved understanding of relationships between those fire drivers. We used 15 years of daily active fire data from the MODIS fire product (MCD14ML, collection 6) to create global maps of six fire descriptors (incidence, size inequality, season length, interannual variability, intensity, and fire season modality). Using multiple correspondence analysis (MCA) and hierarchical agglomerative clustering, we identified three fire macroregimes: Wild, Tamed, and Domesticated, each of which splitting into prototypical and transitional regimes. Interpretation of the six fire regimes in terms of their main drivers relied on the global maps of anthromes and Köppen climate types. The analysis yielded a two-dimensional space where the principal dimension of variability is primarily defined by interannual variability in fire activity and fire season length, and the secondary axis is based mainly on fire incidence. The Wild fire macroregime occurs mostly in cold wildlands, where burning is sporadic and fire seasons are short. Tamed fires predominate in seasonally dry tropical rangelands and croplands with high fire incidence. Domesticated fires are characteristic of humid, warm temperate and tropical croplands and villages with low fire incidence. The Tamed and Domesticated fire macroregimes, representing managed burning, account for 86% of all active fires in our dataset and for 70% of the global burnable area. Fourteen percent of active fires were found in the cold wildlands, and in the rangelands and forests of steppe and desert climates of the Wild macroregime. These results highlight the extent of human control over global pyrogeography in the Anthropocene.

The Impact of Long-Range Transport of Biomass Burning Emissions in Southeast Asia on Southern China

The long-range transport of biomass burning pollutants from Southeast Asia has a significant impact on air quality in China. In this study, the Moderate Resolution Imaging Spectroradiometer (MODIS) fire data and aerosol optical depth (AOD) products and the Tropospheric Monitoring Instrument (TROPOMI) carbon monoxide (CO) data were used to analyze the impact of air pollution caused by biomass burning in Southeast Asia on southern China. Results showed that Yunnan, Guangdong and Guangxi were deeply affected by biomass burning emissions from March to April during 2016–2020. Comparing the data for fires on the Indochinese Peninsula and southern provinces of China, it is obvious that the contribution of pollutants emitted by local biomass burning in China to air pollution is only a small possibility. The distribution of CO showed that the overall emissions increased greatly from March to April, and there was an obvious transmission process. In addition, the MODIS AOD in areas close to the national boundary of China is at a high level (>0.6), and the AOD in the southwest of Guangxi province and the southeast of Yunnan Province is above 0.8. Combined with a typical air pollution event in southern China, the UVAI combined with wind direction and other meteorological data showed that the pollutants were transferred from the Indochinese Peninsula to southern China under the southwest monsoon. The PM2.5 data from ground-based measurements and backward tracking were used to verify the pollutant source of the pollution event, and it was concluded that the degree of pollution in Yunnan, Guangxi and Guangdong provinces was related to the distance from the Indochinese Peninsula. Results indicate that it is necessary to carry out in-depth research on the impact of cross-border air pollution transport on domestic air quality as soon as possible and to actively cooperate with foreign countries to carry out pollution source research and control.

Chemical Structure Regulates the Formation of Secondary Organic Aerosol and Brown Carbon in Nitrate Radical Oxidation of Pyrroles and Methylpyrroles

Nitrogen-containing heterocyclic volatile organic compounds (VOCs) are important components of wildfire emissions that are readily reactive toward nitrate radicals (NO₃) during nighttime, but the oxidation mechanism and the potential formation of secondary organic aerosol (SOA) and brown carbon (BrC) are unclear. Here, NO₃ oxidation of three nitrogen-containing heterocyclic VOCs, pyrrole, 1-methylyrrole (1-MP), and 2-methylpyrrole (2-MP), was investigated in chamber experiments to determine the effect of precursor structures on SOA and BrC formation. The SOA chemical compositions and the optical properties were analyzed using a suite of online and offline instrumentation. Dinitro- and trinitro-products were found to be the dominant SOA constituents from pyrrole and 2-MP, but not observed from 1-MP. Furthermore, the SOA from 2-MP and pyrrole showed strong light absorption, while that from 1-MP were mostly scattering. From these results, we propose that NO₃-initiated hydrogen abstraction from the 1-position in pyrrole and 2-MP followed by radical shift and NO₂ addition leads to light-absorbing nitroaromatic products. In the absence of a 1-position hydrogen, NO₃ addition likely dominates the 1-MP chemistry. We also estimate that the total SOA mass and light absorption from pyrrole and 2-MP are comparable to those from phenolic VOCs and toluene in biomass burning, underscoring the importance of considering nighttime oxidation of pyrrole and methylpyrroles in air quality and climate models.

Climatological Aspects of Active Fires in Northeastern China and Their Relationship to Land Cover

Biomass burning (BB) is a driving force for heavy haze in northeastern China (NEC) and shows distinct seasonal features. However, little is known about its climatological aspects, which are important for regional BB management and understanding BB effects on climate and environment. Here, the climatological characteristics of active fires and their dependence on land cover in NEC were studied using Moderate Resolution Imaging Spectroradiometer (MODIS) products. Moreover, the influence of meteorological factors on fire activities was explored. The number of fires was found to have increased significantly from 2003 to 2018; and the annual total FRP (FRPtot) showed a generally consistent variation with fire counts. However, the mean fire radiative power for each spot (FRPmean) decreased. Fire activity showed distinctive seasonal variations. Most fires and intense burning events occurred in spring and autumn. Spatially, fires were mainly concentrated in cropland areas in plains, where the frequency of fires increased significantly, especially in spring and autumn. The annual percentage of agricultural fires increased from 34% in 2003 to over 60% after 2008 and the FRPtot of croplands increased from 12% to over 55%. Fires in forests, savannas, and grasslands tended to be associated with higher FRPmean than those in croplands. Analysis indicated that the increasing fire count in NEC is mainly caused by agricultural fires. Although the decreasing FRPmean represents an effective management of BB in recent years, high fire counts and FRPtot in croplands indicate that the crop residue burning cannot be simply banned and a need instead for effective applications. More efforts should be made on clean utilization of straw. The accumulation of dry biomass, high temperature, and low humidity, and weak precipitation are conducive to the fire activities. This study provides a comprehensive analysis of BB in NEC and provides a reference for regional BB management and control.

A Pre-Operational System Based on the Assimilation of MODIS Aerosol Optical Depth in the MOCAGE Chemical Transport Model

In this study we present a pre-operational forecasting assimilation system of different types of aerosols. This system has been developed within the chemistry-transport model of Météo-France, MOCAGE, and uses the assimilation of the Aerosol Optical Depth (AOD) from MODIS (Moderate Resolution Imaging Spectroradiometer) onboard both Terra and Aqua. It is based on the AOD assimilation system within the MOCAGE model. It operates on a daily basis with a global configuration of 1∘×1∘ (longitude × latitude). The motivation of such a development is the capability to predict and anticipate extreme events and their impacts on the air quality and the aviation safety in the case of a huge volcanic eruption. The validation of the pre-operational system outputs has been done in terms of AOD compared against the global AERONET observations within two complete years (January 2018–December 2019). The comparison between both datasets shows that the correlation between the MODIS assimilated outputs and AERONET over the whole period of study is 0.77, whereas the biases and the RMSE (Root Mean Square Error) are 0.006 and 0.135, respectively. The ability of the pre-operational system to predict extreme events in near real time such as the desert dust transport and the propagation of the biomass burning was tested and evaluated. We particularly presented and documented the desert dust outbreak which occurred over Greece in late March 2018 as well as the wildfire event which happened on Australia between July 2019 and February 2020. We only presented these two events, but globally the assimilation chain has shown that it is capable of predicting desert dust events and biomass burning aerosols which happen all over the globe.

Saccharides as Particulate Matter Tracers of Biomass Burning: A Review

The adverse effects of atmospheric particulate matter (PM) on health and ecosystems, as well as on meteorology and climate change, are well known to the scientific community. It is therefore undeniable that a good understanding of the sources of PM is crucial for effective control of emissions and to protect public health. One of the major contributions to atmospheric PM is biomass burning, a practice used both in agriculture and home heating, which can be traced and identified by analyzing sugars emitted from the combustion of cellulose and hemicellulose that make up biomass. In this review comparing almost 200 selected articles, we highlight the most recent studies that broaden such category of tracers, covering research publications on residential wood combustions, open-fire or combustion chamber burnings and ambient PM in different regions of Asia, America and Europe. The purpose of the present work is to collect data in the literature that indicate a direct correspondence between biomass burning and saccharides emitted into the atmosphere with regard to distinguishing common sugars attributed to biomass burning from those that have co-causes of issue. In this paper, we provide a list of 24 compounds, including those most commonly recognized as biomass burning tracers (i.e., levoglucosan, mannosan and galactosan), from which it emerges that monosaccharide anhydrides, sugar alcohols and primary sugars have been widely reported as organic tracers for biomass combustion, although it has also been shown that emissions of these compounds depend not only on combustion characteristics and equipment but also on fuel type, combustion quality and weather conditions. Although it appears that it is currently not possible to define a single compound as a universal indicator of biomass combustion, this review provides a valuable tool for the collection of information in the literature and identifies analytes that can lead to the determination of patterns for the distribution between PM generated by biomass combustion.

Variability of Near-Surface Aerosol Composition in Moscow in 2020–2021: Episodes of Extreme Air Pollution of Different Genesis

During 2020–2021, a comprehensive experiment was conducted to study the composition of near-surface atmospheric aerosol in Moscow. The paper considers the experimental data together with synoptic and meteorological conditions. Attention is focused on six episodes of extremely high aerosol mass concentration values: in March and October 2020, as well in March, April, May and July 2021. In all these cases (and only in them), the average daily mass concentration of PM10 aerosol exceeded the Maximum Permissible Concentration (MPC) value (according to Russian standards, 60 μg/m3). The origin of the aerosol during these periods of extreme pollution is revealed, which is the main result of the work. It was shown that the July episode of 2021 was associated with a local intensive anthropogenic source that arose as a result of the active dismantling and demolition of multistory industrial buildings. The remaining spring and autumn episodes were caused by atmospheric transport of both smoke aerosol from various regions with strong biomass fires and dust aerosol from arid zones of the south of European territory of Russia (ETR) with dust wind storms. The cases of atmospheric pollution transport to Moscow region from the other regions are confirmed with the help of air mass transport trajectories (HYSPLIT 4 model) and MERRA-2 reanalysis data on black carbon and/or dust distribution in the atmosphere over ETR. Differences in the elemental composition of the near-surface aerosol of Moscow air during periods with extremely high aerosol concentrations are analyzed in comparison with each other and with unperturbed conditions for the season.

Seven-year study of monsoonal rainwater chemistry over the mid-Brahmaputra plain, India: assessment of trends and source regions of soluble ions

This work is a 7-year study of monsoonal rainwater chemistry (n = 302), over mid-Brahmaputra plain during 2012 to 2018. The samples were analyzed for major chemical parameters viz. pH, electrical conductivity (EC), and ions (SO₄^2-, NO₃^-, Br^-, Cl^-, F^-, Mg²⁺, Ca²⁺, K⁺, NH₄⁺, Na⁺, and Li⁺) to assess the chemistry. The mean pH of rainwater varied among the years, which was maximum in 2018 (6.18 ± 0.72) and minimum in the year 2014 (5.39 ± 0.54), and the variations were significant at p < 0.0001. Ridgeline plots were drawn to visualize interannual variations, which revealed that Ca²⁺ was the dominant cation in the early years, whereas NH₄⁺ prevailed in the latter years. Mann-Kendall analysis and Sen's slope statistical tests were employed, and it was found that all the ions showed positive S values indicating increasing trends. Enrichment factors (EF) of K⁺, SO₄^2-, and NO₃^- were found to be high with respect to both soil and seawater suggesting the influence of emissions from fossil fuel and biomass burning in the chemistry of rainwater. Principal component analysis (PCA) was applied to identify the sources of rain constituents, and five factors were obtained explaining crustal dust, biomass burning, fossil fuel combustion, agricultural emissions, and coal burning as possible sources. Airmass back trajectory clusters and Potential Source Contribution Function (PSCF) were computed by application of HYbrid Single-Particle Lagrangian Integrated Trajectory model to appreciate the terrestrial influence on the chemistry. The results indicated inputs from both local and regional dust and anthropogenic constituents that influenced the monsoonal rainwater chemistry over Brahmaputra Valley.

Crop Residue Burning Emissions and the Impact on Ambient Particulate Matters over South Korea

In the study, crop residue burning (CRB) emissions were estimated based on field surveys and combustion experiments to assess the impact of the CRB on particulate matter over South Korea. The estimates of CRB emissions over South Korea are 9514, 8089, 4002, 2010, 172,407, 7675, 33, and 5053 Mg year−1 for PM10, PM2.5, OC, EC, CO, NOx, SO2, and NH3, respectively. Compared with another study, our estimates in the magnitudes of CRB emissions were not significantly different. When the CRB emissions are additionally considered in the simulation, the monthly mean differences in PM2.5 (i.e., △PM2.5) were marginal between 0.07 and 0.55 μg m−3 over South Korea. Those corresponded to 0.6–4.3% in relative differences. Additionally, the △PM10 was 0.07–0.60 μg m−3 over South Korea. In the spatial and temporal aspects, the increases in PM10 and PM2.5 were high in Gyeongbuk (GB) and Gyeongnam (GN) provinces in June, October, November, and December.

Understanding seasonal variation in ambient air quality and its relationship with crop residue burning activities in an agrarian state of India

In India, Indo-Gangetic Plains (IGP) is becoming the hotspot of air pollution due to increasing anthropogenic activities such as rapid industrial growth, infrastructure development, transportation activities, and seasonal practice of crop residue burning. In the current study, seasonal variation in ambient air quality for 14 parameters, i.e., particulate matter (PM), trace gases, and volatile organic compounds (VOCs), along with meteorological parameters, was studied in 21 districts of the Haryana state for year 2019, situated in IGP. To analyze spatial variation of pollutants, ambient air quality data of 23 continuous ambient air quality monitoring stations were divided into three zones based on ecology and cropping pattern. All the zones showed annual mean PM₁₀ and PM_2.5 concentrations much higher than national ambient air quality standards. Annual mean PM₁₀ concentration (±standard deviation) in Zones-1, 2, and 3 was 156±86, 174±93, and 143±74 μg m^-3, whereas for PM_2.5 was 71±44, 85±54, and 78±47 μg m^-3. The results showed a considerable seasonal variation in the concentration of all pollutants. Most of the pollutants peak in the post-monsoon season, followed by winters in which crop residue burning predominates in many parts of the Haryana. PM₁₀ concentrations increased by 65-112% and PM_2.5 concentrations increased by 131-147% in the post-monsoon season compared to monsoons. The post-monsoon season showed the highest concentration of PM₁₀, NO, and toluene (Zone-1); and PM_2.5, NH₃, CO, and benzene (Zone-2); whereas in winters, SO₂ (Zone-1); ethylbenzene, m,p-xylene, and xylene (Zone-2); and NO₂ and NOx (Zone-3) showed the maximum pollution levels. The O₃ concentration was highest in the pre-monsoon season (Zone-1). The satellite-based fire counts and PCA results show a significant influence of crop residue burning in the post-monsoon season and solid biomass burning in winters on Haryana's air quality. The study could help to understand seasonal variation in ambient air quality and the influence of factors such as crop residue burning in the IGP region, which could help to formulate season-specific control measures to improve regional air quality.

Environmental exposures contribute to respiratory and allergic symptoms among women living in the banana growing regions of Costa Rica

OBJECTIVES

This research evaluates whether environmental exposures (pesticides and smoke) influence respiratory and allergic outcomes in women living in a tropical, agricultural environment.

METHODS

We used data from 266 mothers from the Infants' Environmental Health cohort study in Costa Rica. We evaluated environmental exposures in women by measuring seven pesticide and two polycyclic aromatic hydrocarbons metabolites in urine samples. We defined 'high exposure' as having a metabolite value in the top 75th percentile. We collected survey data on respiratory and allergic outcomes in mothers as well as on pesticides and other environmental exposures. Using logistic regression models adjusted for obesity, we assessed the associations of pesticide exposure with multiple outcomes (wheeze, doctor-diagnosed asthma, high (≥2) asthma score based on symptoms, rhinitis, eczema and itchy rash).

RESULTS

Current pesticide use in the home was positively associated with diagnosed asthma (OR=1.99 (95% CI=1.05 to 3.87)). High urinary levels of 5-hydroxythiabendazole (thiabendazole metabolite) and living in a neighbourhood with frequent smoke from waste burning were associated with a high asthma score (OR=1.84 (95%CI=1.05 to 3.25) and OR=2.31 (95%CI=1.11 to 5.16), respectively). Women who worked in agriculture had a significantly lower prevalence of rhinitis (0.19 (0.01 to 0.93)), but were more likely to report eczema (OR=2.54 (95%CI=1.33 to 4.89)) and an itchy rash (OR=3.17 (95%CI=1.24 to 7.73)).

CONCLUSIONS

While limited by sample size, these findings suggest that environmental exposure to both pesticides and smoke may impact respiratory and skin-related allergic outcomes in women.

Emission factors and chemical characterization of particulate emissions from garden green waste burning

This work provides an evaluation of the emission factors (EFs) of typical garden waste burning (fallen leaves and hedge trimming) in terms of particulate matter (PM), elemental and organic carbon (EC-OC) together with a detailed chemical characterization of 88 particle-bound organic species including polycyclic aromatic hydrocarbons (PAHs), levoglucosan and its isomers, lignin breakdown products (methoxyphenols), cholesterol, alkanes, polyols and sugars. Furthermore, wood-log based burning experiments have been performed to highlight key indicators or chemical patterns of both, green waste and wood burning (residential heating) sources, that may be used for PM source apportionment purposes. Two residential log wood combustion appliances, wood stove (RWS) and fireplace, under different output conditions (nominal and reduced) and wood log moisture content (mix of beech, oak and hornbeam), have been tested. Open wood burning experiments using wood logs were also performed. Green waste burning EFs obtained were comparable to the available literature data for open-air biomass burning. For PM and for most of the organic species studied, they were about 2 to 30 times higher than those observed for wood log combustion experiments. Though, poor performance wood combustions (open-air wood log burning, fireplace and RWS in reduced output) showed comparable EFs for levoglucosan and its isomers, methoxyphenols, polyols, PAHs and sugars. Toxic PAH equivalent benzo[a]pyrene EFs were even 3-10 times higher for the fireplace and open-air wood log burning. These results highlighted the impact of the nature of the fuel burnt and the combustion performances on the emissions. Different chemical fingerprints between both biomass burning sources were highlighted with notably a predominance of odd high-molecular weight n-alkanes (higher carbon preference index, CPI), lower levoglucosan/mannosan ratio and lower sinapylaldehyde abundance for green waste burning. However, the use of such indicators seems limited, especially if applied alone, for a clear discrimination of both sources in ambient air.

Investigation of Forest Fire Activity Changes Over the Central India Domain Using Satellite Observations During 2001-2020

Recurrent and large forest fires negatively impact ecosystem, air quality, and human health. Moderate Resolution Imaging Spectroradiometer fire product is used to identify forest fires over central India domain, an extremely fire prone region. The study finds that from 2001 to 2020, ∼70% of yearly forest fires over the region occurred during March (1,857.5 counts/month) and April (922.8 counts/month). Some years such as 2009, 2012, and 2017 show anomalously high forest fires. The role of persistent warmer temperatures and multiple climate extremes in increasing forest fire activity over central India is comprehensively investigated. Warmer period from 2006 to 2020 showed doubling and tripling of forest fire activity during forest fire (February-June; FMAMJ) and non-fire (July-January; JASONDJ) seasons, respectively. From 2015 JASONDJ to 2018 FMAMJ, central India experienced a severe heatwave, a rare drought and an extremely strong El Niño, the combined effect of which is linked to increased forest fires. Further, the study assesses quinquennial spatiotemporal changes in forest fire characteristics such as fire count density and average fire intensity. Deciduous forests of Jagdalpur-Gadchiroli Range and Indravati National Park in Chhattisgarh state are particularly fire prone (>61 fire counts/grid) during FMAMJ and many forest fires are of high intensity (>45 MW). Statistical associations link high near surface air temperature and low precipitation during FMAMJ to significantly high soil temperature, low soil moisture content, low evapotranspiration and low normalized difference vegetation index. This creates a significantly drier environment, conducive for high forest fire activity in the region.

Atmospheric deposition of inorganic nutrients to the Western North Pacific Ocean

We evaluated the potential impacts of atmospheric deposition on marine productivity and inorganic carbon chemistry in the northwestern Pacific Ocean (8-39°N, 125-157°E). The nutrient concentration in atmospheric total suspended particles decreased exponentially with increasing distance from the closest land-mass (Asia), clearly revealing anthropogenic and terrestrial contributions. The predicted mean depositional fluxes of inorganic nitrogen were approximately 34 and 15 μmol m^-2 d^-1 to the west and east of 140°E, respectively, which were at least two orders of magnitude greater than the inorganic phosphorus flux. On average, atmospheric particulate deposition would support 3-4% of the net primary production along the surveyed tracks, which is equivalent to ~2% of the dissolved carbon increment caused by the penetration of anthropogenic CO₂. Our observations generally fell within the ranges observed over the past 18 years, despite an increasing trend of atmospheric pollution in the source regions during the same period, which implies high temporal and spatial variabilities of atmospheric nutrient concentration in the study area. Continued atmospheric anthropogenic nitrogen deposition may alter the relative abundances of nitrogen and phosphorus.

Atmospheric deposition of biologically relevant trace metals in the eastern Adriatic coastal area

Aerosol (PM₁₀), bulk deposition, sea surface microlayer (SML) and underlying water (ULW) samples were collected simultaneously during a field campaign at the middle Adriatic coastal site between February and July 2019, to assess the impact of atmospheric deposition (AD) of biologically relevant trace metals (TM) (Zn, Cu, Co, Ni, Cd and Pb) on the sea surface responses in an oligotrophic coastal region. Anthropogenic emissions from continental Europe, alongside local/regional domestic heating, likely affected the concentrations of Zn, Cd and Pb in aerosols during winter-early spring, while traffic emissions during the tourist season impacted Ni, Co and Cu aerosol concentrations. Additionally, open-fire biomass burning (BB) episodes caused considerable TM concentration increases, while Saharan dust intrusion in spring led to a 10-fold increase in Co concentrations in PM₁₀ samples. These intensive episodes significantly affected the bulk deposition fluxes of TMs, showing that a small number of such extreme events, common to Mediterranean coastal areas, could be responsible for most of the AD. Enrichments and concentrations of total TMs in SML samples collected following BB events indicated that such events, along with high precipitation, influenced TM partitioning in surface water layers. We estimated that AD represents a significant source of TM to the shallow middle Adriatic coastal area, highlighting the need to further explore the atmosphere-sea surface links, to expand our understanding of the biogeochemistry of these important micronutrients and pollutants, including their impact on the aquatic community.

Effects of Stand Structure and Topography on Forest Vegetation Carbon Density in Jiangxi Province

Stand structure and topography are important factors affecting forest vegetation carbon density (FVCD). Revealing the interaction mechanisms between stand structure and topography on FVCD is of great significance for enhancing forest vegetation carbon storage and achieving regional carbon neutrality. Based on stratified sampling, systematic distribution and forest continuous inventory sample plots in Jiangxi province, the variation characteristics of FVCD and its correlations with stand structure and topographic factors were studied. The results are as follows: (1) The average FVCD in Jiangxi province was 44.23 Mg/ha, which was dominated by the carbon density of the arbor layer, accounting for about 81.39% of the total forest—far lower than the average level of global FVCD, which proved that the forest in Jiangxi province was dominated by middle-age and young forests with low carbon density, and also showed that the potential for forest vegetation carbon storage in Jiangxi province was huge. (2) Except for vegetation carbon densities of shrub and herb layers, the vegetation carbon densities of other forest layers in Jiangxi province were significantly different among different forest types. Volume per unit area was the most important factor affecting the vegetation carbon densities of arbor and total forest, and vegetation carbon density–volume models of the main forests were built for vegetation carbon density calculation in Jiangxi province. (3) The vegetation carbon densities of arbor layer, snag and log layer, and total forest increased significantly with increases in elevation and slope. Except for the shrub layer and herb layer, the vegetation carbon densities of the other layers and the total forest had extremely significant or significant differences between slope position gradients—indicating that the effect of topography on FVCD in Jiangxi province was significant, mainly through influencing of forest distribution and human disturbance intensity.

Biomass Burning Over the United States East Coast and Western North Atlantic Ocean: Implications for Clouds and Air Quality

Biomass burning (BB) aerosol events were characterized over the U.S. East Coast and Bermuda over the western North Atlantic Ocean (WNAO) between 2005 and 2018 using a combination of ground-based observations, satellite data, and model outputs. Days with BB influence in an atmospheric column (BB days) were identified using criteria biased toward larger fire events based on anomalously high AERONET aerosol optical depth (AOD) and MERRA-2 black carbon (BC) column density. BB days are present year-round with more in June-August (JJA) over the northern part of the East Coast, in contrast to more frequent events in March-May (MAM) over the southeast U.S. and Bermuda. BB source regions in MAM are southern Mexico and by the Yucatan, Central America, and the southeast U.S. JJA source regions are western parts of North America. Less than half of the BB days coincide with anomalously high PM2.5 levels in the surface layer, according to data from 14 IMPROVE sites over the East Coast. Profiles of aerosol extinction suggest that BB particles can be found in the boundary layer and into the upper troposphere with the potential to interact with clouds. Higher cloud drop number concentration and lower drop effective radius are observed during BB days. In addition, lower liquid water path is found during these days, especially when BB particles are present in the boundary layer. While patterns are suggestive of cloud-BB aerosol interactions over the East Coast and the WNAO, additional studies are needed for confirmation.

Tracers from Biomass Burning Emissions and Identification of Biomass Burning

The major organic compositions from biomass burning emissions are monosaccharide derivatives from the breakdown of cellulose, generally accompanied by small amounts of straight-chain, aliphatic, oxygenated compounds, and terpenoids from vegetation waxes, resins/gums, and other biopolymers. Levoglucosan from cellulose can be utilized as a specific or general indicator for biomass combustion emissions in aerosol samples. There are other important compounds, such as dehydroabietic acid, syringaldehyde, syringic acid, vanillic acid, vanillin, homovanillic acid, 4-hydroxybenzoic acid, and p-coumaric acid, which are additional key indicators of biomass burning. In this review, we will address these tracers from different types of biomass burning and the methods used to identify the sources in ambient aerosols. First, the methods of inferring biomass burning types by the ratio method are summarized, including levoglucosan/mannose, syringic acid/vanillic acid, levolgucosan/K+, vanillic acid/4-hydroxybenzoic acid, levoglucosan/OC, and levoglucosan/EC to infer the sources of biomass burning, such as crop residual burning, wheat burning, leaf burning, peatland fire, and forest fire in Asia. Second, we present the source tracer ratio methods that determine the biomass combustion types and their contributions. Finally, we introduce the PCA (Principal component analysis) and PMF (Positive matrix factor) methods to identify the type of biomass burning and its contributions according to emission factors of different species in various plants such as softwood, hardwood, and grass.

The particle phase state during the biomass burning events

The phase state of biomass burning aerosols (BBA) remains largely unclear, impeding our understanding of their effects on air quality, climate and human health, due to its profound roles in mass transfer between gaseous and particulate phase. In this study, the phase state of BBA was investigated by measuring the particle rebound fraction ƒ combining field observations and laboratory experiments. We found that both ambient and laboratory-generated BBA had unexpectedly lower rebound fraction ƒ (<0.6) under the dry conditions (RH = 20-50%), indicating that BBA were in non-solid state at such low RH. This was obviously different from the secondary organic aerosols (SOA) derived from the oxidation of both anthropogenic and biogenic volatile organic compounds, typically with a rebound fraction ƒ larger than 0.8 at RH below 50%. Therefore, we proposed that the diffusion coefficient of gaseous molecular in the bulk of BBA might be much higher than SOA under the dry conditions.

Quantifying the high resolution seasonal emission of air pollutants from crop residue burning in India

Biomass burning, a recurring global phenomenon is also considered an environmental menace, making headlines every year in India with onset of autumn months. Agriculture is demographically the broadest economic sector and plays a significant role in the overall socio-economic fabric of India. Hence, disposal of crop residue is done mainly by burning leading to deterioration of air quality. Residue burning in parts of India is blamed for changing air quality in nearby cities. The spatial distribution of these emissions has always been a challenge due to various data constraints. We hereby present a comprehensive spatially resolved seasonal high resolution gridded (∼10 km × ∼10 km) emission inventory of major pollutants from crop residue burning source in India for the latest year 2018. The winter months contributes almost around ∼50% of total emission followed by summer (∼48%), which is the prime cause of changing air quality in nearby cities. Among all the crops; rice, wheat, maize and sugarcane accounts ∼90% of total PM₁₀ load in the country. The estimated emission for PM_2.5, PM₁₀, BC and OC, CO, NOx, SO₂, VOC, CH₄ and CO₂ are found to 990.68 Gg/yr, 1231.26 Gg/yr, 123.33 Gg/yr, 410.99 Gg/yr, 11208.18 Gg/yr, 484.55 Gg/yr, 144.66 Gg/yr, 1282.95 Gg/yr, 785.56 Gg/yr and 262051.06 Gg/yr respectively. The cropping pattern and its role in different geographic regions are analysed to identify all potential emission hotspots regions scattered across the country. The developed gridded emissions inventory is envisaged to serve as an important input to regional atmospheric chemistry transport model to better quantify its contribution in deteriorating air quality in various regions of India, paving the way to policy makers to better plan the mitigation and control strategies. The developed fundamental tool is likely to be useful for air quality management.

The significance of pyrogenic polycyclic aromatic hydrocarbons in Borneo peat core for the reconstruction of fire history

The reconstruction of fire history is essential to understand the palaeoclimate and human history. Polycyclic aromatic hydrocarbons (PAHs) have been extensively used as a fire marker. In this work, the distribution of PAHs in Borneo peat archives was investigated to understand how PAHs reflect the palaeo-fire activity. In total, 52 peat samples were analysed from a Borneo peat core for the PAH analysis. Pyrogenic PAHs consist of 2–7 aromatic rings, some of which have methyl and ethyl groups. The results reveal that the concentration of pyrogenic PAHs fluctuated with the core depth. Compared to low-molecular-weight (LMW) PAHs, the high-molecular-weight (HMW) PAHs had a more similar depth variation to the charcoal abundance. This finding also suggests that the HMW PAHs were mainly formed at a local fire near the study area, while the LMW PAHs could be transported from remote locations.

Observations of supermicron-sized aerosols originating from biomass burning in southern Central Africa

During the 3 years of the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) campaign, the NASA Orion P-3 was equipped with a 2D stereo (2D-S) probe that imaged particles with maximum dimension (D) ranging from 10 < D < 1280 μm. The 2D-S recorded supermicron-sized aerosol particles (SAPs) outside of clouds within biomass burning plumes during flights over the southeastern Atlantic off Africa's coast. Numerous SAPs with 10 < D < 1520 μm were observed in 2017 and 2018 at altitudes between 1230 and 4000 m, 1000 km from the coastline, mostly between 7-11° S. No SAPs were observed in 2016 as flights were conducted further south and further from the coastline. Number concentrations of refractory black carbon (rBC) measured by a single particle soot photometer ranged from 200 to 1200 cm^-3 when SAPs were observed. Transmission electron microscopy images of submicron particulates, collected on Holey carbon grid filters, revealed particles with potassium salts, black carbon (BC), and organics. Energy-dispersive X-ray spectroscopy spectra also detected potassium, a tracer for biomass burning. These measurements provided evidence that the submicron particles originated from biomass burning. NOAA Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) 3 d back trajectories show a source in northern Angola for times when large SAPs were observed. Fire Information for Resource Management System (FIRMS) Moderate Resolution Imaging Spectroradiometer (MODIS) 6 active fire maps showed extensive biomass burning at these locations. Given the back trajectories, the high number concentrations of rBC, and the presence of elemental tracers indicative of biomass burning, it is hypothesized that the SAPs imaged by the 2D-S are examples of BC aerosol, ash, or unburned plant material.

Fire Diurnal Cycle Derived from a Combination of the Himawari-8 and VIIRS Satellites to Improve Fire Emission Assessments in Southeast Australia

The violent and persistent wildfires that broke out along the southeast coast of Australia in 2019 caused a large number of pollutant emissions, which seriously affected air quality and the global climate. The existing two methods for estimating combustion emissions based on burned area and fire radiative power mainly use a medium resolution imaging spectrometer (MODIS) on the Aqua and Terra satellites. However, the low temporal resolution of MODIS and insensitivity to small fires lead to deviation in the estimation of fire emissions. In order to solve this problem, the Visible Infrared Imaging Radiometer Suite (VIIRS) with better performance is adopted in this paper, combined with the fire diurnal cycle information obtained by geostationary satellite Himawari-8, to explore the spatio-temporal model of biomass combustion emissions. Using this, a high-spatial- and -temporal-resolution fire emission inventory was generated for southeastern Australia from November 2019 to January 2020, which aims to fully consider the highly dynamic nature of fires and small fires (low FRP) that are much lower than the MODIS burned area or active fire detection limit, with emphasis on dry matter burned (DMB). We found that during the study period, the fire gradually moved from north to south, and the diurnal cycle of the fire in the study area changed greatly. The peak time of the fire gradually delayed as the fire moved south. Our inventory shows that the DMB in southeast Australia during the study period was about 146 Tg, with major burned regions distributed along the Great Dividing Range, with December 2019 being the main burning period. The total DMB we calculated is 0.5–3.1 times that reported by the GFAS (Global Fire Assimilation System) and 1.5 to 4 times lower than that obtained using the traditional “Burned Area Based Method (FINN)”. We believe that the GFAS may underestimate the results by ignoring a large number of small fires, and that the excessive combustion rate used in the FINN may be a source of overestimation. Therefore, we conclude that the combination of high-temporal-resolution and high-spatial-resolution satellites can improve FRE estimation and may also allow further verification of biomass combustion estimates from different inventories, which are far better approaches for fire emission estimation.

Qualitative Study on the Observations of Emissions, Transport, and the Influence of Climatic Factors from Sugarcane Burning: A South African Perspective

There are two methods of harvesting sugarcane—manual or mechanical. Manual harvesting requires the burning of the standing sugarcane crop. Burning of the crop results in the emission of aerosols and harmful trace gases into the atmosphere. This work makes use of a long-term dataset (1980–2019) to study (1) the atmospheric spatial and vertical distribution of pollutants; (2) the spatial distribution and temporal change of biomass emissions; and (3) the impact/influence of climatic factors on temporal change in atmospheric pollutant loading and biomass emissions over the Mpumalanga and KwaZulu Natal provinces in South Africa, where sugarcane farming is rife. Black carbon (BC) and sulfur dioxide (SO₂) are two dominant pollutants in the JJA and SON seasons due to sugarcane burning. Overall, there was an increasing trend in the emissions of BC, SO₂, and carbon dioxide (CO₂) from 1980 to 2019. Climatic conditions, such as warm temperature, high wind speed, dry conditions in the JJA, and SON season, favor the intensity and spread of the fire, which is controlled. The emitted pollutants are transported to neighboring countries and can travel over the Atlantic Ocean, as far as ~6600 km from the source site.