Comparing levoglucosan and mannosan ratios in sediments and corresponding aerosols from recent Australian fires

The monosaccharide anhydrides levoglucosan, mannosan, and galactosan are known as 'fire sugars' as they are powerful proxies used to trace fire events. Despite their increasing use, their application is not completely understood, especially in the context of tracing past fire events using sediment samples. There are many uncertainties about fire sugar formation, partitioning, transport, complexation, and stability along all stages of the source-to-sink pathway. While these uncertainties exist, the efficacy of fire sugars as fire tracers remains limited. This study compared high-resolution fire sugar fluxes in freshwater sediment cores to known fire records in Tasmania, Australia. Past fire events correlated with fire sugar flux increases down-core, with the magnitude of the flux inversely proportional to the distance of the fires from the study site. For the first time, fire sugar ratios (levoglucosan/mannosan, L/M) in aerosols were compared with those in sediments from the same time-period. The L/M ratio in surface sediments (1.42-2.58) were significantly lower than in corresponding aerosols (5.08-15.62). We propose two hypotheses that may explain the lower average L/M of sediments. Firstly, the degradation rate of levoglucosan is higher than mannosan in the water column, sediment-water interface, and/or sediment. Secondly, the L/M ratio of non-atmospheric emissions during fires may be lower than that of atmospheric emissions from the same fire. Due to the uncertainties about transport partitioning (atmospheric versus non-atmospheric emissions) and fire sugar degradation along all stages of the source-to-sink pathway, we advise caution when inferring vegetation type (e.g. softwood, hardwood, or grasses) based purely on fire sugar ratios in sediments (e.g. L/M ratio). Future investigations are required to increase the efficacy of fire sugars as a complimentary, or standalone, fire tracer in sediments.

Influence of meteorological factors on open biomass burning at a background site in Northeast China

Biomass burning (BB) is a very important emission source that significantly adversely impacts regional air quality. BB produces a large number of primary organic aerosol (POA) and black carbon (BC). Besides, BB also provides many precursors for secondary organic aerosol (SOA) generation. In this work, the ratio of levoglucosan (LG) to organic carbon (OC) and the fire hotspots map was used to identify the open biomass burning (OBB) events, which occurred in two representative episodes, October 13 to November 30, 2020, and April 1 to April 30, 2021. The ratio of organic aerosol (OA) to reconstructed PM2.5 concentration (PM2.5*) increased with the increase of LG/OC. When LG/OC ratio is higher than 0.03, the highest OA/PM2.5* ratio can reach 80%, which means the contribution of OBB to OA is crucial. According to the ratio of LG to K+, LG to mannosan (MN) and the regional characteristics of Longfengshan, it can be determined that the crop residuals are the main fuel. The occurrence of OBB coincides with farmers' preferred choices, i.e., burning biomass in "bright weather". The "bright weather" refers to the meteorological conditions with high temperature, low humidity, and without rain. Meteorological factors indirectly affect regional biomass combustion pollution by influencing farmers' active choices.

Simulating spatio-temporal dynamics of surface PM2.5 emitted from Alaskan wildfires

Wildfire is a major disturbance agent in Arctic boreal and tundra ecosystems that emits large quantities of atmospheric pollutants, including PM2.5. Under the substantial Arctic warming which is two to three times of global average, wildfire regimes in the high northern latitude regions are expected to intensify. This imposes a considerable threat to the health of the people residing in the Arctic regions. Alaska, as the northernmost state of the US, has a sizable rural population whose access to healthcare is greatly limited by a lack of transportation and telecommunication infrastructure and low accessibility. Unfortunately, there are only a few air quality monitoring stations across the state of Alaska, and the air quality of most remote Alaskan communities is not being systematically monitored, which hinders our understanding of the relationship between wildfire emissions and human health within these communities. Models simulating the dispersion of pollutants emitted by wildfires can be extremely valuable for providing spatially comprehensive air quality estimates in areas such as Alaska where the monitoring station network is sparse. In this study, we established a methodological framework that is based on an integration of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, the Wildland Fire Emissions Inventory System (WFEIS), and the Arctic-Boreal Vulnerability Experiment (ABoVE) Wildfire Date of Burning (WDoB) dataset, an Arctic-oriented fire product. Through our framework, daily gridded surface-level PM2.5 concentrations for the entire state of Alaska between 2001 and 2015 for which wildfires are responsible can be estimated. This product reveals the spatio-temporal patterns of the impacts of wildfires on the regional air quality in Alaska, which, in turn, offers a direct line of evidence indicating that wildfire is the dominant driver of PM2.5 concentrations over Alaska during the fire season. Additionally, it provides critical data inputs for research on understanding how wildfires affect human health which creates the basis for the development of effective and efficient mitigation efforts.

Aqueous processing of water-soluble organic compounds in the eastern United States during winter

Aqueous multi-phase processes are significant contributors to organic aerosol (OA) mass in the atmosphere. This study characterizes the formation of water-soluble organic matter during the winter in the eastern United States through simultaneous measurements of water-soluble organic carbon in the gas and particle phases (WSOC_g and WSOC_p, respectively). The formation of secondary WSOC_p occurred primarily through two pathways: (1) absorptive partitioning of oxygenated organics to the bulk OA and (2) aqueous phase processes. WSOC_p formation through the former pathway was evident through the relationship between the fraction of total WSOC in the particle phase (F_p) and the total OA concentration. Conversely, evidence for nighttime aqueous WSOC_p formation was based upon the strong enhancement in F_p with increasing relative humidity, indicating the uptake of WSOC_g to aerosol liquid water (ALW). The F_p-RH relationship was only observed for temperatures between 0-10 °C, suggesting conditions for aqueous multi-phase processes were enhanced during these times. Temperature exhibited an inverse relationship with ALW and a proportional relationship with aerosol potassium. ALW and biomass burning precursors were both abundant in the 0-10 °C temperature range, facilitating aqueous WSOC_p formation. To assess the impact of particle drying on the WSOC_p concentrations, the particle measurements alternated between ambient and dried channels. No change was observed in the concentration of particles before and after drying, indicating that the WSOC_p formed through the uptake of WSOC_g into OA and ALW remained in the condensed phase upon particle drying at all temperature ranges. This work contributes to our understanding of sources, pathways, and factors affecting aqueous aerosol formation in the winter.

Beyond the Ångström Exponent: Probing Additional Information in Spectral Curvature and Variability of In Situ Aerosol Hyperspectral (0.3-0.7 μm) Optical Properties

Ångström exponents (α) allow reconstruction of aerosol optical spectra over a broad range of wavelengths from measurements at two or more wavelengths. Hyperspectral measurements of atmospheric aerosols provide opportunities to probe measured spectra for information inaccessible from only a few wavelengths. Four sets of hyperspectral in situ aerosol optical coefficients (aerosol-phase total extinction, σ _ext, and absorption, σ _abs; liquid-phase soluble absorption from methanol, σ _MeOH-abs, and water, σ _DI-abs, extracts) were measured from biomass burning aerosols (BBAs). Hyperspectral single scattering albedo (ω), calculated from σ _ext and σ _abs, provide spectral resolution over a wide spectral range rare for this optical parameter. Observed spectral shifts between σ _abs and σ _MeOH-abs/σ _DI-abs argue in favor of measuring σ _abs rather than reconstructing it from liquid extracts. Logarithmically transformed spectra exhibited curvature better fit by second-order polynomials than linear α. Mapping second order fit coefficients (a ₁, a ₂) revealed samples from a given fire tended to cluster together, that is, aerosol spectra from a given fire were similar to each other and somewhat distinct from others. Separation in (a ₁, a ₂) space for spectra with the same α suggest additional information in second-order parameterization absent from the linear fit. Spectral features found in the fit residuals indicate more information in the measured spectra than captured by the fits. Above-detection σ _MeOH-abs at 0.7 μm suggests assuming all absorption at long visible wavelengths is BC to partition absorption between BC and brown carbon (BrC) overestimates BC and underestimates BrC across the spectral range. Hyperspectral measurements may eventually discriminate BBA among fires in different ecosystems under variable conditions.

PM2.5 in Carlsbad Caverns National Park: Composition, sources, and visibility impacts

Carlsbad Caverns National Park in southeastern New Mexico is adjacent to the Permian Basin, one of the most productive oil and gas regions in the country. The 2019 Carlsbad Caverns Air Quality Study (CarCavAQS) was designed to examine the influence of regional sources, including urban emissions, oil and gas development, wildfires, and soil dust on air quality in the park. Field measurements of aerosols, trace gases, and deposition were conducted from 25 July through 5 September 2019. Here, we focus on observations of fine particles and key trace gas precursors to understand the important contributing species and their sources and associated impacts on haze. Key gases measured included aerosol precursors, nitric acid and ammonia, and oil and gas tracer, methane. High-time resolution (6-min) PM_2.5 mass ranged up to 31.8 µg m^-3, with an average of 7.67 µg m^-3. The main inorganic ion contributors were sulfate (avg 1.3 µg m^-3), ammonium (0.30 µg m^-3), calcium (Ca²⁺) (0.22 µg m^-3), nitrate (0.16 µg m^-3), and sodium (0.057 µg m^-3). The WSOC concentration averaged 1.2 µg C m^-3. Sharp spikes were observed in Ca²⁺, consistent with local dust generation and transport. Ion balance analysis and abundant nitric acid suggest PM_2.5 nitrate often reflected reaction between nitric acid and sea salt, forming sodium nitrate, and between nitric acid and soil dust containing calcium carbonate, forming calcium nitrate. Sulfate and soil dust are the major contributors to modeled light extinction in the 24-hr average daily IMPROVE observations. Higher time resolution data revealed a maximum 1-hr extinction value of 90 Mm^-1 (excluding coarse aerosol) and included periods of significant light extinction from BC as well as sulfate and soil dust. Residence time analysis indicated enrichment of sulfate, BC, and methane during periods of transport from the southeast, the direction of greatest abundance of oil and gas development.Implications: Rapid development of U.S. oil and gas resources raises concerns about potential impacts on air quality in National Parks. Measurements in Carlsbad Caverns National Park provide new insight into impacts of unconventional oil and gas development and other sources on visual air quality in the park. Major contributors to visibility impairment include sulfate, soil dust (often reacted with nitric acid), and black carbon. The worst periods of visibility and highest concentrations of many aerosol components were observed during transport from the southeast, a region of dense Permian Basin oil and gas development.

A fast, single column high performance anion exchange chromatography with pulsed amperometric detection method for determination of saccharides in atmospheric aerosol samples

Saccharides, especially anhydro sugars present in atmospheric aerosols, can be used as tracers to track sources of atmospheric aerosol. High-performance anion-exchange chromatography with pulsed amperometric detection is a commonly used technique for determining these saccharides, but the reported methods suffer from three drawbacks. One, to achieve separation of the complete set of atmospheric saccharides, run times are very long, typically longer than 60 minutes. Two, some methods require two columns to achieve the desired separation. Finally, in an era when electrolytic eluent preparation allows for excellent precision and accuracy, these methods require manually prepared eluents, which can lead to separation inconsistency for closely eluting analytes. These drawbacks make existing methods difficult to automate. To address this issue, we developed a fast method that uses only a single column for separation, and electrolytically generated eluent that resolves 12 key atmospheric aerosol saccharides in 20 minutes. The resolved saccharides include anhydro sugars (levoglucosan, galactosan, and mannosan), sugar alcohols (erythritol, xylitol, and mannitol), and mono-/disaccharides (arabinose, galactose, glucose, mannose, fructose, and sucrose). To our knowledge this report is the first instance of achieving such significant reduction in run time with good resolution for this set of saccharides. This article is protected by copyright. All rights reserved.

Examining the status of forest fire emission in 2020 and its connection to COVID-19 incidents in West Coast regions of the United States

Forest fires impact on soil, water, and biota resources. The current forest fires in the West Coast of the United States (US) profoundly impacted the atmosphere and air quality across the ecosystems and have caused severe environmental and public health burdens. Forest fire led emissions could significantly exacerbate the air pollution level and, therefore, would play a critical role if the same occurs together with any epidemic and pandemic health crisis. Limited research is done so far to examine its impact in connection to the current pandemic. As of October 21, nearly 8.2 million acres of forest area were burned, with more than 25 casualties reported so far. In-situ air pollution data were utilized to examine the effects of the 2020 forest fire on atmosphere and coronavirus (COVID-19) casualties. The spatial-temporal concentrations of particulate matter (PM_2.5 and PM₁₀) and Nitrogen Dioxide (NO₂) were collected from August 1 to October 30 for 2020 (the fire year) and 2019 (the reference year). Both spatial (Multiscale Geographically Weighted Regression) and non-spatial (Negative Binomial Regression) analyses were performed to assess the adverse effects of fire emission on human health. The in-situ data-led measurements showed that the maximum increases in PM_2.5, PM₁₀, and NO₂ concentrations (μg/m³) were clustered in the West Coastal fire-prone states during August 1 - October 30, 2020. The average concentration (μg/m³) of particulate matter (PM_2.5 and PM₁₀) and NO₂ was increased in all the fire states severely affected by forest fires. The average PM_2.5 concentrations (μg/m³) over the period were recorded as 7.9, 6.3, 5.5, and 5.2 for California, Colorado, Oregon, and Washington in 2019, increasing up to 24.9, 13.4, 25.0, and 17.0 in 2020. Both spatial and non-spatial regression models exhibited a statistically significant association between fire emission and COVID-19 incidents. Such association has been demonstrated robust and stable by a total of 30 models developed for analyzing the spatial non-stationary and local association. More in-depth research is needed to better understand the complex relationship between forest fire emission and human health.

Impacts of chemical degradation of levoglucosan on quantifying biomass burning contribution to carbonaceous aerosols: A case study in Northeast China

Biomass burning (BB) is an important source of carbonaceous aerosols in Northeast China (NEC). Quantifying the original contribution of BB to organic carbon (OC) [BB-OC] can provide an essential scientific information for the policy-makers to formulate the control measures to improve the air quality in the NEC region. Daily PM_2.5 samples were collected in the rural area of Changchun city over the NEC region from May 2017 to May 2018. In addition to carbon contents, BB tracers (e.g., levoglucosan and K⁺_BB, defined as potassium from BB) were also determined, in order to investigate the relative contribution of BB-OC. The results showed that OC was the dominant (28%) components of PM_2.5 during the sampling period. Higher concentrations of OC, levoglucosan, and K⁺_BB were observed in the autumn followed by the winter, spring, and summer, indicating that the higher BB activities during autumn and winter in Changchun. By using the Bayesian mixing model, it was found that burning of crop residues were the dominant source (65-79%) of the BB aerosols in Changchun. During the sampling period, the aging in air mass (AAM) ratio was 0.14, indicating that ~86% of levoglucosan in Changchun was degraded. Without considering the degradation of levoglucosan in the atmosphere, the BB-OC ratios were 23%, 28%, 7%, and 4% in the autumn, winter, spring, and summer, respectively, which were 1.4-4.8 time lower than those (14-42%) with consideration of levoglucosan degradation. This illustrated that the relative contribution of BB to OC would be underestimated (~59%) without considering degradation effects of levoglucosan. Although some uncertainty was existed in our estimation, our results did highlight that the control of straw burning was an efficient way to decrease the airborne PM_2.5, improving the air quality in the NEC plain.

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.

New open burning policy reshaped the aerosol characteristics of agricultural fire episodes in Northeast China

The massive agricultural sector in the Northeast Plain, which is of great importance for the food security in China, results in a huge amount of crop residues and thus substantial concern on haze pollution due to biomass burning (BB). To seek for effective control measures on BB emissions, a dramatic transition of open burning policy occurred in Heilongjiang Province, from the "legitimate burning" policy released in 2018 to the "strict prohibition" policy implemented in 2019 and beyond. Here we explored the BB aerosols during 2020-2021 in Harbin, the capital city of Heilongjiang. Although open burning was strictly prohibited by mandatory bans, agricultural fires were not actually eliminated, as indicated by the levoglucosan levels and fire count results. In general, the BB aerosols in Harbin were attributed to the overlaying of household burning and agricultural fire emissions. The former factor laid the foundation of biomass burning impacts, with BB contributions to organic carbon and elemental carbon (f_BBOC and f_BBEC) of 35 and 47%, respectively. The latter further enhanced the BB impacts during specific episodes breaking out in the spring of 2021 as well as the fall of 2020, when f_BBOC and f_BBEC increased to 64 and 57%, respectively. In addition, comparing to the fires of 2018-2019 which occurred in winter (in response to the "legitimate burning" policy), the agricultural fires were shifted to spring and fall in the 2020-2021 campaign, accompanied with an increase of combustion efficiency. This study illustrated how the agricultural fire emissions were influenced by the transition of open burning policy.

Saccharides in atmospheric particulate and sedimentary organic matter: Status overview and future perspectives

Saccharides are omnipresent compounds in terrestrial and marine ecosystems. Since the 2000s, their role in environmental and geochemical studies has significantly increased, but only anhydrosaccharides (mainly levoglucosan) have been reviewed. Here we present the wider knowledge about saccharides in organic matter of aerosols, bottom sediments, soils, dust, and sedimentary rocks. The main purpose here is to characterize the possible sources of saccharides, as well as sacharol formation, seasonal variability, and the possible applications in environmental and paleoenvironmental interpretations. Different saccharide sources were designated, including biomass burning, and particulate matter such as pollen, spores, lichen, and fungi, as well as polysaccharide decomposition as possible inputs of monosaccharides. The main focus was on the most common saccharides encountered in environmental samples and sedimentary rocks. These are the mono- and disaccharides glucose, fructose, sucrose, and trehalose, and sacharols arabitol and mannitol. The anhydrosaccharides levoglucosan, mannosan, and galactosan were evaluated as ancient wildfire indicators and industrialization tracers found in lacustrine sediments starting from Pleistocene to contemporary deposits. However, other anhydrosaccharides like xylosan and arabinosan were also found as products of fossil wood burning. These anhydrosaccharides have the potential to be further tracers of hemicellulose burning. Additional recommendations are proposed for future research, including environmental and paleoenvironmental topics that need to be addressed.

Personal exposure to PM2.5 of indoor and outdoor origin in two neighboring Chinese communities with contrasting household fuel use patterns

The Chinese government is replacing high-polluting, household coal heating stoves with electricity- and natural gas-powered heaters to improve ambient air quality. The evaluation of the intervention impact on outdoor PM_2.5 and personal exposure in community level are in their initial stages. We compared outdoor air pollution and personal exposure in two neighboring communities (~2 km) in northern China with contrasting household fuel use patterns: one where residents primarily used coal for cooking and heating ("coal village") and one where natural gas was the dominant fuel ("gas village"). We collected 24-h outdoor gravimetric PM_2.5 samples in each village and concurrently measured 48-h integrated exposures among 71 participants from 41 and 30 households in the coal and gas villages, respectively. PM_2.5 samples were analyzed for mass and chemical composition. Daily outdoor PM_2.5 concentrations in the coal village (mean ± standard deviation: 109 ± 41 μg/m³) were, on average, 1.3 ± 0.2 times higher than in the gas village (88 ± 38 μg/m³). However, personal PM_2.5 exposures were lower in the coal village (116 ± 121 μg/m³ versus 156 ± 106 μg/m³). PM_2.5 species that can serve as tracers for residential coal combustion (e.g., S, Se, Zn, Pb, etc.) and dust (Al, Ca, Mg, Fe, Si and Ti) were higher in the coal village, and the proportion of personal PM_2.5 of outdoor origin in the coal village was nearly 2 times higher than the gas village. Our results suggest that ambient PM_2.5 and its chemical composition can vary at relatively small spatial scales and may reflect community-level differences in the household energy use. However, personal PM_2.5 exposures may not mirror between-village differences in outdoor air pollution if only PM_2.5 mass is evaluated. Individual chemical composition of PM_2.5 exposure can provide important insight in future studies on the effectiveness of source-targeted air quality interventions.

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.

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.

Seasonal and temporal variations of ambient aerosols in a deciduous broadleaf forest from northern Japan: Contributions of biomass burning and biological particles

Total suspended particulate (TSP) samples were collected in a deciduous broadleaf forest in Sapporo, Hokkaido, Japan, from January to December 2010 to understand the molecular composition and abundance of sugar compounds (SCs) in atmospheric aerosols. We analyzed the samples for anhydrosugars, primary sugars, and sugar alcohols using a gas chromatograph-mass spectrometer. The annual mean concentrations of total SCs ranged from 16.1 to 1748 ng m^-3 (avg. 311 ng m^-3) with maxima in spring (avg. 484 ng m^-3) and minima in winter (avg. 28.2 ng m^-3). Primary sugars and sugar alcohols followed the seasonal pattern of total SCs. High levels of anhydrosugars in winter (avg. 22.9 ng m^-3) suggest a contribution of biomass burning from domestic heating due to lower ambient temperature. The high levels of arabitol and mannitol in spring followed by summer and autumn denote the contribution from multiple sources, i.e., growing vegetation and fungal spores in Sapporo forest. We observed an enhanced contribution of bioaerosols emitted from plant blossoms in spring and leaf decomposition in autumn. The identical seasonal trends of glucose and trehalose implied their similar sources in forest aerosols. Conversely, the highest concentration of sucrose in spring was due to the pollen emissions by blooming plants. Positive matrix factorization (PMF) analyses of the SCs suggested that organic aerosols in the deciduous forest are associated with the emissions from multiple sources, including vegetation, microbes, pollens, and wintertime biomass burning. The PMF analysis also suggested that vegetation is the primary carbon source in the forest atmosphere. The diagnostic mass ratios of levoglucosan to mannosan demonstrated the dominance of softwood burning. We noted that the meteorological parameters substantially affect the emission sources and seasonal concentrations of SCs in the deciduous forest.

Evolution of secondary inorganic aerosols amidst improving PM2.5 air quality in the North China plain

The Clean Air Action implemented by the Chinese government in 2013 has greatly improved air quality in the North China Plain (NCP). In this work, we report changes in the chemical components of atmospheric fine particulate matter (PM_2.5) at four NCP sampling sites from 2012/2013 to 2017 to investigate the impacts and drivers of the Clean Air Action on aerosol chemistry, especially for secondary inorganic aerosols (SIA). During the observation period, the concentrations of PM_2.5 and its chemical components (especially SIA, organic carbon (OC), and elemental carbon (EC)) and the frequency of polluted days (daily PM_2.5 concentration ≥ 75 μg m^-3) in the NCP, declined significantly at all four sites. Asynchronized reduction in SIA components (large decreases in SO₄^2- with stable or even increased NO₃^- and NH₄⁺) was observed in urban Beijing, revealing a shift of the primary form of SIA, which suggested the fractions of NO₃^- increased more rapidly than SO₄^2- during PM_2.5 pollution episodes, especially in 2016 and 2017. In addition, unexpected increases in the sulfur oxidation ratio (SOR) and the nitrogen oxidation ratio (NOR) were observed among sites and across years in the substantially decreased PM_2.5 levels. They were largely determined by secondary aerosol precursors (i.e. decreased SO₂ and NO₂), photochemical oxidants (e.g. increased O₃), temperature, and relative humidity via gas-phase and heterogeneous reactions. Our results not only highlight the effectiveness of the Action Plan for improving air quality in the NCP, but also suggest an increasing importance of SIA in determining PM_2.5 concentration and composition.

Peat-forest burning smoke in Maritime Continent: Impacts on receptor PM2.5 and implications at emission sources

This study characterizes the impacts of transported peat-forest (PF) burning smoke on an urban environment and evaluates associated source burning conditions based on carbon properties of PM_2.5 at the receptor site. We developed and validated a three-step classification that enables systematic and more rapid identification of PF smoke impacts on a tropical urban environment with diverse emissions and complex atmospheric processes. This approach was used to characterize over 300 daily PM_2.5 data collected during 2011-2013, 2015 and 2019 in Singapore. A levoglucosan concentration of ≥0.1 μg/m³ criterion indicates dominant impacts of transported PF smoke on urban fine aerosols. This approach can be used in other ambient environments for practical and location-dependent applications. Organic carbon (OC) concentrations (as OC indicator) can be an alternate to levoglucosan for assessing smoke impacts on urban environments. Applying the OC concentration indicator identifies smoke impacts on ∼80% of daily samples in 2019 and shows an accuracy of 51-86% for hourly evaluation. Following the systematic identification of urban PM_2.5 predominantly affected by PF smoke in 2011-2013, 2015 and 2019, we assessed the concentration ratio of char-EC/soot-EC as an indicator of smoldering- or flaming-dominated burning emissions. When under the influence of transported PF smoke, the mean concentration ratio of char-EC to soot-EC in urban PM_2.5 decreased by >70% from 8.2 in 2011 to 2.3 in 2015 but increased to 3.8 in 2019 (p < 0.05). The reversed trend with a 65% increase from 2015 to 2019 shows stronger smoldering relative to flaming, indicating a higher level of soil moisture at smoke origins, possibly associated with rewetting and revegetating peatlands since 2016.

Differential Cardiopulmonary Health Impacts of Local and Long-Range Transport of Wildfire Smoke

We estimated cardiopulmonary morbidity and mortality associated with wildfire smoke (WFS) fine particulate matter (PM_2.5) in the Front Range of Colorado from 2010 to 2015. To estimate WFS PM_2.5, we developed a daily kriged PM_2.5 surface at a 15  × 15 km resolution based on the Environmental Protection Agency Air Quality System monitors for the western United States; we subtracted out local seasonal-average PM_2.5 of nonsmoky days, identified using satellite-based smoke plume estimates, from the local daily estimated PM_2.5 if smoke was identified by National Oceanic and Atmospheric Administration's Hazard Mapping System. We implemented time-stratified case-crossover analyses to estimate the effect of a 10 µg/m³ increase in WFS PM_2.5 with cardiopulmonary hospitalizations and deaths using single and distributed lag models for lags 0-5 and distinct annual impacts based on local and long-range smoke during 2012, and long-range transport of smoke in 2015. A 10 µg/m³ increase in WFS was associated with all respiratory, asthma, and chronic obstructive pulmonary disease hospitalizations for lag day 3 and hospitalizations for ischemic heart disease at lag days 2 and 3. Cardiac arrest deaths were associated with WFS PM_2.5 at lag day 0. For 2012 local wildfires, asthma hospitalizations had an inverse association with WFS PM_2.5 (OR: 0.716, 95% CI: 0.517-0.993), but a positive association with WFS PM_2.5 during the 2015 long-range transport event (OR: 1.455, 95% CI: 1.093-1.939). Cardiovascular mortality was associated with the 2012 long-range transport event (OR: 1.478, 95% CI: 1.124-1.944).

Postharvest Burning of Crop Residues in Home Stoves in a Rural Site of Daejeon, Korea: Its Impact to Atmospheric Carbonaceous Aerosol

To investigate the impact of burning postharvest crop residues in home stoves, PM2.5 samples (particulate matter with a diameter of <2.5 μm) were collected every 3 h at a rural site in Daejeon, Korea during the postharvest season in 2014. A high concentration of levoglucosan was observed with a peak value of 3.8 µg/m3 during the sampling period. The average mannosan/levoglucosan ratio (0.18) at the rural site during a severe BB episode (levoglucosan > 1 μg/m3) was similar to burnings of pepper stems (0.19) and bean stems (0.18) whereas the average OC/levoglucosan ratio (9.9) was similar to burning of pepper stems (10.0), implying that the severe BB episode was mainly attributed to burning of pepper stems. A very strong correlation was observed between levoglucosan and organic carbon (OC) (R2 = 0.81) during the entire sampling period, suggesting that the emission of organic aerosols at the rural site was strongly associated with the burning of crop residues in home stoves. The average mannosan/levoglucosan ratio (0.17 ± 0.06) in the rural area was similar to that in a nearby urban area in Daejeon (0.16 ± 0.04). It was concluded that crop residue burning in a home stove for space heating is one of the important sources of carbonaceous aerosols not only in a rural area but also in the urban area of Daejeon, Korea during the postharvest season.

First High-Resolution Emission Inventory of Levoglucosan for Biomass Burning and Non-Biomass Burning Sources in China

Levoglucosan (LG) emitted from non-biomass burning (non-BB) sources has given rise to biased or even unreasonable source identification results when adopting LG as a distinct marker of biomass burning (BB). The estimation of LG emission and its spatiotemporal variation for various sources are the keys to reducing uncertainty. This study first developed a LG emission inventory for China from 25 sub-type sources belonging to eight categories, with a 3 km × 3 km spatial resolution and monthly distribution. The total LG emission in 2014 was 145.7 Gg. Domestic BB and open BB contributed 39.2 and 34.3% of the total emission. Non-BB sources, including municipal solid waste burning (9.7%), firework burning (9.6%), meat cooking (5.4%), domestic coal burning (1.5%), ritual item burning (0.2%), and industrial coal burning (0.1%), contributed to 26.5% of the total emission. LG emission varied spatially and temporally. Non-BB sources have a significant spatiotemporal impact on BB source contributions, even in high BB emission regions or in sowing, harvesting, and winter heating seasons. The local BB contributions have been substantially overestimated by 4.28-369% in previous studies, wherein LG was solely referred to as the BB source. By 2018, LG emission from BB might decrease to 63.9% of its total emission. This high-resolution LG emission inventory can be greatly useful for source identification studies in China. It also supports future research on the modeling of smoke aging and pollution control.

Atmospheric particle-bound polycyclic aromatic hydrocarbons, n-alkanes, hopanes, steranes and trace metals: PM2.5 source identification, individual and cumulative multi-pathway lifetime cancer risk assessment in the urban environment

The occurrence of atmospheric fine particles (PM_2.5)-associated polycyclic aromatic hydrocarbons (PAHs), trace metals and organic molecular markers was investigated by conducting an intensive sampling campaign at the Eastern Mediterranean urban area of Nicosia (Cyprus). Sixty-two 24-hr PM_2.5 samples were collected and analyzed for fifty parent and alkylated PAHs, twenty-five long chain n-alkanes, seventeen hopanes and twelve steranes used for source apportionment. The same number and kind of samples were analyzed to determine twenty-eight trace metals. Emphasis was given to investigate the air levels of the scarcely monitored although highly carcinogenic PAHs such as dibenzopyrenes, dibenzoanthracenes, 7H-benzo[c]fluorene and 5-methyl-chrysene, not included in the USEPA's sixteen PAH priority list (USEPA-16). UNMIX receptor model was applied to apportion the sources of atmospheric emissions of the determined organic compounds and trace metals and evaluate their daily contributions to the corresponding PM_2.5 associated concentrations. For comparison purposes, principal component analysis with multiple linear regression (PCA/MLR) was also applied and its results are reported. The UNMIX receptor model, compared to PCA/MLR, offered a more precise source profile and more reliable daily mass source distributions by eliminating negative contributions. The individual and cumulative multi-pathway lifetime cancer risk (posed via inhalation, ingestion and dermal contact) by exposure to PM_2.5-associated USEPA-16 listed and non-listed PAHs and selected airborne trace metals (As, Cd, Co, Ni, and Pb) were assessed. To estimate the contribution of each emission source to the total cancer risk, multiple linear regression analysis was performed, using as independent variables the daily source mass contributions and as dependent variables the respective cancer risk units. The estimated total cumulative cancer risk comprising all toxic PAHs, besides those included in the priority list, and metals was higher than the USEPA's threshold by a factor of eight, denoting a potential risk for long-term exposure of a population in the urban environment.

Quantifying the relative importance of major tracers for fine particles released from biofuel combustion in households in the rural North China Plain

Biomass burning tracers have been widely used to identify biomass burning types, but such tools can sometimes cause large uncertainties in the source attribution studies of PM_2.5 (particles with an aerodynamic diameter of smaller than 2.5 μm). To quantify the relative importance of the major biomass burning tracers in PM_2.5 released from biofuels combusted in the North China Plain, combustion experiments under the smoldering and flaming combustion conditions were conducted using nine types of typical household biofuels including two types of agricultural wastes, five types of hardwoods, one softwood, and one mixed wood briquette. PM_2.5 samples were collected from the combustion experiments and source profiles of PM_2.5 were thus determined for various biofuels under the two different combustion conditions. Carbonaceous species including organic carbon (OC) and elemental carbon (EC) were the major chemical components of the PM_2.5 released from combustion of all the tested biofuels, with mass fractions of 37-45% and 4-7% under the smoldering condition and 11-25% and 7-29% under the flaming condition, respectively. Higher mass fractions of water-soluble inorganic ions (WSIIs, e.g., K⁺ and Cl^-) in PM_2.5 were observed under the flaming than smoldering combustion condition, while anhydrosugars (levoglucosan (LG) and mannosan (MN)) presented in an opposite pattern. The average LG/MN ratio in PM_2.5 changed significantly with biofuel type (20-55 for agricultural wastes, 10-22 for hardwoods (except elm) and 3-6 for softwood), but varied little with combustion condition. In contrast, the K⁺/LG ratio in PM_2.5 varied significantly between smoldering (<0.2) and flaming (>0.6) combustion conditions for all the biofuel types except softwood. Results from this study suggested that the ratio LG/MN was the best tracer for identifying the biofuel types and the ratio K⁺/LG is suitable for identifying the combustion conditions in this region.

Comparison of physical and chemical characteristics and oxidative potential of fine particles emitted from rice straw and pine stem burning

Agricultural burning and forest fires are common in Northeast Asia and contribute to the elevation of fine particulate pollution, which greatly affects air quality. In this study, chemical and physical attributes, as well as the oxidative potential of fine particles produced from rice straw and pine stem burning in a laboratory-scale chamber were determined. The burning of rice straw generated notably lower emissions of fine particles and elemental carbon (EC) than did the burning of pine stems. The longer retention of ultrafine particles was observed for rice straw burning likely caused by this material's longer period of initial flaming combustion. Organic carbon (OC), OC/EC, K⁺/OC, K⁺/EC, Zn, and alkanoic acid were higher in the fine particles of rice straw burning, while EC, K⁺/Cl^-, Fe, Cr, Al, Cu, and levoglucosan were higher for pine stem burning particles. Chemical data were consistent with a higher hygroscopic growth factor and cloud formation potential and lower amount of agglomerated soot for rice straw burning particles. Rice straw burning particles displayed an oxidative potential seven times higher than that of pine stems.

Estimating the air quality and health impacts of biomass burning in northern South America using a chemical transport model

Biomass burning (BB) emissions significantly deteriorate air quality in many regions worldwide, impact human health and perturbing Earth's radiation budget and climate. South America is one of largest contributors to BB emissions globally. After Amazonia, BB emissions from open and agricultural fires of Northern South America (NSA) are the most significant. Recent evidence shows a strong correlation between fire counts in NSA and Brown Carbon in some Colombian cities, suggesting a substantial seasonal contribution of regional BB sources to air pollution levels in the densely populated areas of NSA. In this work we use the atmospheric regional chemical transport model WRF-Chem to assess the contribution of open BB events to pollutant concentration and to estimate potential health impacts associated with wildfire events in NSA. Three nested domains are used to simulate atmospheric composition in the Northern part of South America and the Caribbean. Simulations included biogenic and anthropogenic emissions from a global emission inventory merged with local emissions for the city of Bogotá. Two modelling scenarios were considered, a base case without BB emissions (NO_FIRE) and a sensitivity scenario with BB emissions. Simulations were carried out for periods of strong BB activity in NSA. In the NO_FIRE scenario, aerosol concentrations are unrealistically low. When BB emissions are is included background PM_2.5 concentrations increase 80%. The increment in aerosol concentrations is mainly driven by Secondary Organic Aerosols. In the case of Bogotá, the most densely populated city in the domain, monthly mean increase in PM_2.5 is 3.3 μg m^-3 and 4.3 ppb for O₃. Modeled meteorological and air pollution fields are in better agreement with observations when high spatial resolution (3 × 3 km) is used in the simulations. The total estimated short-term all-cause mortality associated to BB during February in the region is 171 cases, 88 PM_2.5-related and 83 O₃-related mortality.

Composition and source apportionment of saccharides in aerosol particles from an agro-industrial zone in the Indo-Gangetic Plain

The characterization of saccharidic compounds in atmospheric aerosols is important in order to retrieve information about organic carbon sources and their transport pathways through the atmosphere. In this study, composition and sources of saccharides in PM₁₀ were determined in a South Asian megacity (Faisalabad) during the year 2015 - 2016. PM₁₀ sampled on quartz filters was analyzed by anion exchange chromatography for the selected saccharidic compounds. The average PM₁₀ concentration was found to be 744 ± 392 μg m^-3, exceeding the daily limits proposed by Pak-EPA (150 μg m^-3), US-EPA (150 μg m^-3), and WHO (50 μg m^-3). The average total saccharidic concentration was found to be 2820 ± 2247 ng m^-3. Among the different saccharidic categories, anhydrosugars were the most abundant in concentration followed by primary sugars and sugar alcohols. The correlation and principal component analysis indicated emissions from biomass combustion, soil suspensions from areas such as farmlands having high microorganism activity, and biogenic emissions such as airborne fungal spores and vegetation detritus as major sources of saccharides in the aerosol samples.

Assessment of Ambient Air Toxics and Wood Smoke Pollution among Communities in Sacramento County

Ambient air monitoring and phone survey data were collected in three environmental justice (EJ) and three non-EJ communities in Sacramento County during winter 2016–2017 to understand the differences in air toxics and in wood smoke pollution among communities. Concentrations of six hazardous air pollutants (HAPs) and black carbon (BC) from fossil fuel (BC_ff) were significantly higher at EJ communities versus non-EJ communities. BC from wood burning (BC_wb) was significantly higher at non-EJ communities. Correlation analysis indicated that the six HAPs were predominantly from fossil fuel combustion sources, not from wood burning. The HAPs were moderately variable across sites (coefficient of divergence (COD) range of 0.07 for carbon tetrachloride to 0.28 for m- and p-xylenes), while BC_ff and BC_wb were highly variable (COD values of 0.46 and 0.50). The BC_wb was well correlated with levoglucosan (R² of 0.68 to 0.95), indicating that BC_wb was a robust indicator for wood burning. At the two permanent monitoring sites, wood burning comprised 29–39% of the fine particulate matter (PM_2.5) on nights when PM_2.5 concentrations were forecasted to be high. Phone survey data were consistent with study measurements; the only significant difference in the survey results among communities were that non-EJ residents burn with indoor devices more often than EJ residents.

Carbonaceous Aerosol Emitted from Biofuel Household Stove Combustion in South China

Near-source measurements of smoke emissions from household stove combustion in a rural area of South China were conducted with 7 typical biomass fuels. Particulate matter samples (both PM10 and PM2.5) were analyzed for their carbonaceous components, including organic and elemental carbon (OC, EC) as well as levoglucosan (molecular tracer of biomass burning), employing thermal-optical and GC-MS analysis. The OC and EC content in PM2.5 and PM10 smoke particles derived from the various types of vegetation showed different patterns with the smallest values observed for straw type fuels. The OC/EC ratios in PM2.5 and PM10 showed an order of straw > hardwood > bamboo > softwood. Mass concentrations of particulate matter emitted from rice straw burning were highest with 12.23 ± 0.87 mg/m3 (PM10) and 9.31 ± 0.81 mg/m3 (PM2.5), while the mass ratios (LG/PM and OC/PM) were lowest among the 7 fuels, indicating that particle emissions from straw burning were higher than those from woody fuels, using similar burning conditions. The levoglucosan emission ratios were rather high and this single most abundant organic species was mainly present in the fine particle mode. Linear correlation analysis showed a strong relationship between levoglucosan and EC emissions.

Use of IoT sensing and occupant surveys for determining the resilience of buildings to forest fire generated PM2.5

Wildfires and associated emissions of particulate matter pose significant environmental and health concerns. In this study we propose tools to evaluate building resilience to extreme episodes of outdoor particulate matter using a combination of indoor and outdoor IoT measurements, coupled with survey-based information of occupants' perception and behaviour. We demonstrated the application of the tools on two buildings with different modes of ventilation during the Chico Camp fire event. We characterized the resilience of the buildings on different temporal and spatial scales using the well-established I/O ratio and a newly proposed E-index that evaluates indoor concentration in the context of adopted 24-hour exposure thresholds. Indoor PM2.5 concentration during the entire Chico Camp Fire event was 21 μg/m3 for 4th Street (Mechanically Ventilated) and 36 μg/m3 for Wurster Hall (Naturally Ventilated). The cumulative median I/O ratio during the fire event was 0.27 for 4th Street and 0.67 for Wurster Hall. Overall E-index for 4th Street was 0.82, suggesting that the whole building was resilient to outdoor air pollution while overall E-index was 1.69 for Wurster Hall suggesting that interventions are necessary. The survey revealed that occupant perception of workplace air quality aligns with measured PM2.5 in the two buildings. The results also highlight that a large portion of occupants wore face masks, even though the PM2.5 concentration was below WHO threshold level. The results of our study demonstrate the utility of the proposed IoT-enabled and survey tools to assess the degree of protection from air pollution of outdoor origin for a single building or across a portfolio of buildings. The proposed survey tool also provides direct links between the PM2.5 levels and occupants' perception and behavior.

A Laboratory Assessment of 120 Air Pollutant Emissions from Biomass and Fossil Fuel Cookstoves

Cookstoves emit many pollutants that are harmful to human health and the environment. However, most of the existing scientific literature focuses on fine particulate matter (PM2.5) and carbon monoxide (CO). We present an extensive data set of speciated air pollution emissions from wood, charcoal, kerosene, and liquefied petroleum gas (LPG) cookstoves. One-hundred and twenty gas- and particle-phase constituents-including organic carbon, elemental carbon (EC), ultrafine particles (10-100 nm), inorganic ions, carbohydrates, and volatile/semivolatile organic compounds (e.g., alkanes, alkenes, alkynes, aromatics, carbonyls, and polycyclic aromatic hydrocarbons (PAHs))-were measured in the exhaust from 26 stove/fuel combinations. We find that improved biomass stoves tend to reduce PM2.5 emissions; however, certain design features (e.g., insulation or a fan) tend to increase relative levels of other coemitted pollutants (e.g., EC ultrafine particles, carbonyls, or PAHs, depending on stove type). In contrast, the pressurized kerosene and LPG stoves reduced all pollutants relative to a traditional three-stone fire (≥93% and ≥79%, respectively). Finally, we find that PM2.5 and CO are not strong predictors of coemitted pollutants, which is problematic because these pollutants may not be indicators of other cookstove smoke constituents (such as formaldehyde and acetaldehyde) that may be emitted at concentrations that are harmful to human health.

Molecular markers for biomass burning associated with the characterization of PM2.5 and component sources during dry season haze episodes in Upper South East Asia

Severe air pollution in the form of smoke haze in the northern part of Southeast Asia (SEA) occurs annually in the dry season due to huge open area burning. Molecular markers of biomass burning were investigated by characterization of fine particles (PM_2.5) collected in the dry season (23 February-28 April 2016). The average PM_2.5, organic carbon (OC) and elemental carbon (EC) concentrations were 64.3 ± 17.6 μg m^-3, 23.6 ± 8.1 μg m^-3 and 2.85 ± 0.98 μg m^-3, respectively. SO₄^2- was the dominant species (8.73 ± 2.88 μg m^-3) of water-soluble ion, followed by NH₄⁺ (3.32 ± 1.01 μg m^-3) and NO₃^- (2.70 ± 0.51 μg m^-3). High concentrations of the biomass burning tracers K⁺ (1.27 ± 0.38 μg m^-3) and levoglucosan (1.22 ± 0.75 μg m^-3) were observed. The ratios of levoglucosan/K⁺ (0.92 ± 0.35) and levoglucosan/mannosan (20.4 ± 4.1) identified forest and agricultural waste burning as major contributors to the aerosol. Strong correlations (r > 0.800) between levoglucosan and OC, K⁺, anhydrosugar isomer (mannosan and galactosan) and other saccharides (mannose, arabitol and mannitol) verified that combustion of biomass was the major source of organic compounds associated with PM_2.5 aerosols. Oxalate was the most abundant (0.75 ± 0.17 μg m^-3; 53%) of the carboxylates. The concentration of oxalate was strongly correlated to that of PM_2.5 (r = 0.799) and levoglucosan (r = 0.615), indicating that oxalate originates mainly from primary emissions from biomass burning rather than secondary formation from photochemical processes. Backward trajectories indicated that long-range transport air masses influencing air quality in Northern Thailand originated to the west and southwest.

Assessment of forest fire impacts on carbonaceous aerosols using complementary molecular marker receptor models at two urban locations in California's San Joaquin Valley

Two hundred sixty-three fine particulate matter (PM_2.5) samples were collected over fourteen months in Fresno and Bakersfield, California. Samples were analyzed for organic carbon (OC), elemental carbon (EC), water soluble organic carbon (WSOC), and 160 organic molecular markers. Chemical Mass Balance (CMB) and Positive Matrix Factorization (PMF) source apportionment models were applied to the results in order to understand monthly and seasonal source contributions to PM_2.5 OC. Similar source categories were found from the results of the CMB and PMF models to PM_2.5 OC across the sites. Six source categories with reasonably stable profiles, including biomass burning, mobile, food cooking, two different secondary organic aerosols (SOAs) (i.e., winter and summer), and forest fires were investigated. Both the CMB and the PMF models showed a strong seasonality in contributions of some sources, as well as dependence on wind transport for both sites. The overall relative source contributions to OC were 24% CMB wood smoke, 19% CMB mobile sources, 5% PMF food cooking, 2% CMB vegetative detritus, 17% PMF SOA summer, 22% PMF SOA winter, and 12% PMF forest fire. Back-trajectories using the Weather Research and Forecasting model combined with the FLEXible PARTicle dispersion model (WRF-FLEXPART) were used to further characterize wind transport. Clustering of the trajectories revealed dominant wind patterns associated with varying concentrations of the different source categories. The Comprehensive Air Quality Model with eXtensions (CAMx) was used to simulate aerosol transport from forest fires and thus confirm the impacts of individual fires, such as the Rough Fire, at the measurement sites.

Distribution, sources and potential health risks of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 collected during different monsoon seasons and haze episode in Kuala Lumpur

This study aimed to determine the distribution and potential health risks of polycyclic aromatic hydrocarbons (PAHs) in PM_2.5 collected in Kuala Lumpur during different monsoon seasons. The potential sources of PM_2.5 were investigated using 16 priority PAHs with additional of biomass tracers namely levoglucosan (LV), mannosan (MN) and galactosan (GL). This study also investigated the cytotoxic potential of the extracted PAHs towards V79-4 cells. A high-volume air sampler (HVS) was used to collect PM_2.5 samples for 24 h. PAHs were extracted using dichloromethane (DCM) while biomass tracers were extracted by a mixture of DCM/methanol (3:1) before analysis with gas chromatography-mass spectrometry (GC-MS). The cytotoxicity of the PAHs extract was determined by assessing the cell viability through the reduction of tetrazolium salts (MTT). The results showed that the total mean ± SD concentrations of PAHs during the southwest (SW) and northeast (NE) monsoons were 2.51 ± 0.93 ng m^-3 and 1.37 ± 0.09 ng m^-3, respectively. Positive matrix factorization (PMF) using PAH and biomass tracer concentrations suggested four potential sources of PM_2.5; gasoline emissions (29.1%), natural gas and coal burning (28.3%), biomass burning (22.3%), and diesel and heavy oil combustion (20.3%). Health risk assessment showed insignificant incremental lifetime cancer risk (ILCR) of 2.40E-07 for 70 years of exposure. MTT assay suggested that PAHs extracts collected during SW monsoon have cytotoxic effect towards V79-4 cell at the concentrations of 25 μg mL^-1, 50 μg mL^-1, 100 μg mL^-1 whereas non-cytotoxic effect was observed on the PAHs sample collected during NE monsoon.

Residential Coal Combustion as a Source of Levoglucosan in China

Levoglucosan (LG) has been widely identified as a specific marker for biomass burning (BB) sources and frequently utilized in estimating the BB contribution to atmospheric fine particles all over the world. However, this study provides direct evidence to show that coal combustion (CC) is also a source of LG, especially in the wintertime in Northern China, based on both source testing and ambient measurement. Our results show that low-temperature residential CC could emit LG with emission factors (EF) ranging from 0.3 to 15.9 mg kg^-1. Ratios of LG to its isomers, mannosan and galactosan, differ between CC and BB emissions, and the wintertime ratios in Beijing ambient PM_2.5 and source-specific tracers including carbon isotopic signatures all indicated a significant contribution from CC to ambient levoglucosan in winter in Beijing. The results suggest that LG cannot be used as a distinct source marker for biomass burning in special cases such as some cities in the northern China, where coal is still widely used in the residential and industrial sectors. Biomass burning sources could be overestimated, although such an over-estimation could vary spatially and temporally.

The health impacts and economic value of wildland fire episodes in the U.S.: 2008-2012

INTRODUCTION

Wildland fires degrade air quality and adversely affect human health. A growing body of epidemiology literature reports increased rates of emergency departments, hospital admissions and premature deaths from wildfire smoke exposure.

OBJECTIVE

Our research aimed to characterize excess mortality and morbidity events, and the economic value of these impacts, from wildland fire smoke exposure in the U.S. over a multi-year period; to date no other burden assessment has done this.

METHODS

We first completed a systematic review of the epidemiologic literature and then performed photochemical air quality modeling for the years 2008 to 2012 in the continental U.S. Finally, we estimated the morbidity, mortality, and economic burden of wildland fires.

RESULTS

Our models suggest that areas including northern California, Oregon and Idaho in the West, and Florida, Louisiana and Georgia in the East were most affected by wildland fire events in the form of additional premature deaths and respiratory hospital admissions. We estimated the economic value of these cases due to short term exposures as being between $11 and $20B (2010$) per year, with a net present value of $63B (95% confidence intervals $6-$170); we estimate the value of long-term exposures as being between $76 and $130B (2010$) per year, with a net present value of $450B (95% confidence intervals $42-$1200).

CONCLUSION

The public health burden of wildland fires-in terms of the number and economic value of deaths and illnesses-is considerable.

Origin of Fine Particulate Carbon in the Rural United States

Carbonaceous compounds are a significant component of fine particulate matter and haze in national parks and wilderness areas where visibility is protected, i.e., class I areas (CIAs). The Regional Haze Rule set the goal of returning visibility in CIAs on the most anthropogenically impaired days to natural by 2064. To achieve this goal, we need to understand contributions of natural and anthropogenic sources to the total fine particulate carbon (TC). A Lagrangian chemical transport model was used to simulate the 2006-2008 contributions from various source types to measured TC in CIAs and other rural lands. These initial results were incorporated into a hybrid model to reduce systematic biases. During summer months, fires and vegetation-derived secondary organic carbon together often accounted for >75% of TC. Smaller contributions, <20%, from area and mobile sources also occurred. During the winter, contributions from area and mobile sources increased, with area sources accounting for half or more of the TC in many regions. The area emissions were likely primarily from residential and industrial wood combustion. Different fire seasons were evident, with the largest contributions during the summer when wildfires occur and smaller contributions during the spring and fall when prescribed and agricultural fires regularly occur.

Characterization and seasonal variations of levoglucosan in fine particulate matter in Xi'an, China

PM2.5 (particulate matter with an aerodynamic diameter <2.5 microm) samples (n = 58) collected every sixth day in Xi'an, China, from 5 July 2008 to 27 June 2009 are analyzed for levoglucosan (1,6-anhydro-beta-D-glucopyranose) to evaluate the impacts of biomass combustion on ambient concentrations. Twenty-four-hour levoglucosan concentrations displayed clear summer minima and winter maxima that ranged from 46 to 1889 ng m(-3), with an average of 428 +/- 399 ng m(-3). Besides agricultural burning, biomass/biofuel combustion for household heating with straws and branches appears to be of regional importance during the heating season in northwestern China. Good correlations (0.70 < R < 0.91) were found between levoglucosan relative to water- soluble K+, Cl-, organic carbon (OC), elemental carbon (EC), and glyoxal. The highest levoglucosan/OC ratio of2.3% wasfound in winter, followed by autumn (1.5%). Biomass burning contributed to 5.1-43.8% of OC (with an average of 17.6 +/- 8.4%).

The characteristics of Beijing aerosol during two distinct episodes: impacts of biomass burning and fireworks

The chemical composition of Beijing aerosol was measured during summer and winter. Two distinct episodes were identified. Water-soluble potassium (K(+)) increased significantly during the firework episode in winter with an episode to non-episode ratio of 4.97, whereas the biomass burning (BB) episode in summer was characterized by high episode to non-episode ratios of levoglucosan (6.38) and K(+) (6.90). The BB and firework episodes had only a minor influence on the water-soluble OC (organic carbon) to OC ratio. Based on separate investigations of episode and non-episode periods, it was found that: (i) sulfate correlated strongly with both relative humidity and nitrate during the typical winter period presumably indicating the importance of the aqueous-phase oxidation of sulfur dioxide by nitrogen dioxide, (ii) oxalate and WSOC during both winter and summer in Beijing were mainly due to secondary formation, and (iii) high humidity can significantly enhance the formation potential of WSOC in winter.

Air quality impact and physicochemical aging of biomass burning aerosols during the 2007 San Diego wildfires

Intense wildfires burning >360000 acres in San Diego during October, 2007 provided a unique opportunity to study the impact of wildfires on local air quality and biomass burning aerosol (BBA) aging. The size-resolved mixing state of individual particles was measured in real-time with an aerosol time-of-flight mass spectrometer (ATOFMS) for 10 days after the fires commenced. Particle concentrations were high county-wide due to the wildfires; 84% of 120-400 nm particles by number were identified as BBA, with particles <400 nm contributing to mass concentrations dangerous to public health, up to 148 μg/m(3). Evidence of potassium salts heterogeneously reacting with inorganic acids was observed with continuous high temporal resolution for the first time. Ten distinct chemical types shown as BBA factors were identified through positive matrix factorization coupled to single particle analysis, including particles comprised of potassium chloride and organic nitrogen during the beginning of the wildfires, ammonium nitrate and amines after an increase of relative humidity, and sulfate dominated when the air mass back trajectories passed through the Los Angeles port region. Understanding BBA aging processes and quantifying the size-resolved mass and number concentrations are important in determining the overall impact of wildfires on air quality, health, and climate.

Biomass burning contributions to urban aerosols in a coastal Mediterranean city

Mean annual biomass burning contributions to the bulk particulate matter (PM(X)) load were quantified in a southern-European urban environment (Barcelona, Spain) with special attention to typical Mediterranean winter and summer conditions. In spite of the complexity of the local air pollution cocktail and the expected low contribution of biomass burning emissions to PM levels in Southern Europe, the impact of these emissions was detected at an urban background site by means of tracers such as levoglucosan, K(+) and organic carbon (OC). The significant correlation between levoglucosan and OC (r(2)=0.77) and K(+) (r(2)=0.65), as well as a marked day/night variability of the levoglucosan levels and levoglucosan/OC ratios was indicative of the contribution from regional scale biomass burning emissions during night-time transported by land breezes. In addition, on specific days (21-22 March), the contribution from long-range transported biomass burning aerosols was detected. Quantification of the contribution of biomass burning aerosols to PM levels on an annual basis was possible by means of the Multilinear Engine (ME). Biomass burning emissions accounted for 3% of PM(10) and PM(2.5) (annual mean), while this percentage increased up to 5% of PM(1). During the winter period, regional-scale biomass burning emissions (agricultural waste burning) were estimated to contribute with 7±4% of PM(2.5) aerosols during night-time (period when emissions were clearly detected). Long-range transported biomass burning aerosols (possibly from forest fires and/or agricultural waste burning) accounted for 5±2% of PM(2.5) during specific episodes. Annually, biomass burning emissions accounted for 19%-21% of OC levels in PM(10), PM(2.5) and PM(1). The contribution of this source to K(+) ranged between 48% for PM(10) and 97% for PM(1) (annual mean). Results for K(+) from biomass burning evidenced that this tracer is mostly emitted in the fine fraction, and thus coarse K(+) could not be taken as an appropriate tracer of biomass burning.

Levoglucosan and carbonaceous species in the background aerosol of coastal southeast China: case study on transport of biomass burning smoke from the Philippines

INTRODUCTION

Levoglucosan and carbonaceous species in the background aerosol of coastal southeast China were measured at Jianfengling (JFL), a background mountain site in a National Reserve Park on Hainan Island, and at Hok Tsui (HT), a rural site on the southern coast of Hong Kong from April to May of 2004 during an intensive field study.

METHODS

We integrated the information from field study, satellite and backward trajectory model to examine the long-range transport of biomass burning smoke from the Philippines and assess its impact on background aerosol in coastal southeast China.

RESULTS AND DISCUSSION

The average levoglucosan concentrations were 42 and 30 ng m(-3) at JFL and HT, respectively, while the organic and elemental carbon concentrations were 3.1 and 0.4 μg C m(-3) respectively at JFL, and 4.1 and 1.3 μg C m(-3) respectively at HT. Elevated levoglucosan concentrations of 85-106 ng m(-3) (250-340% extra loadings) at JFL and 57 ng m(-3) (170% extra loading) at HT were observed during transport events in which air masses originated from the Philippines. Fire hot spot counts and aerosol index derived from satellite data showed that the spread of biomass burning smoke from the Philippines resulted in large-scale dense aerosol clouds in the adjacent South China Sea and the western Pacific Ocean. The observed high ratio of two biomass-burning tracers (levoglucosan to mannosan) at JFL (7-36) and HT (27) indicated that the biomass smoke originating from the Philippines had significant contributions from open-field burning of agricultural residues, such as rice straw. The pollution plumes were transported to southeast China resulting in elevated concentrations of carbonaceous aerosol and levoglucosan in particular. Using a simplified receptor-based approach, biomass smoke aerosol was estimated to account for 16-28% of OC in the background atmosphere of Hainan and 4.9% of OC at the rural site of Hong Kong during these episode cases, indicating that biomass burning smoke generated in the Philippines could have a significant contribution to background ambient aerosol of southeast coastal China.

Chemically-resolved volatility measurements of organic aerosol fom different sources

A newly modified fast temperature-stepping thermodenuder (TD) was coupled to a High Resolution Time-of-Flight Aerosol Mass Spectrometer for rapid determination of chemically resolved volatility of organic aerosols (OA) emitted from individual sources. The TD-AMS system was used to characterize primary OA (POA) from biomass burning, trash burning surrogates (paper and plastic), and meat cooking as well as chamber-generated secondary OA (SOA) from alpha-pinene and gasoline vapor. Almost all atmospheric models represent POA as nonvolatile, with no allowance for evaporation upon heating or dilution, or condensation upon cooling. Our results indicate that all OAs observed show semivolatile behavior and that most POAs characterized here were at least as volatile as SOA measured in urban environments. Biomass-burning OA (BBOA) exhibited a wide range of volatilities, but more often showed volatility similar to urban OA. Paper-burning resembles some types of BBOA because of its relatively high volatility and intermediate atomic oxygen-to-carbon (O/C) ratio, while meat-cooking OAs (MCOA) have consistently lower volatility than ambient OA. Chamber-generated SOA under the relatively high concentrations used intraditional experiments was significantly more volatile than urban SOA, challenging extrapolation of traditional laboratory volatility measurements to the atmosphere. Most OAs sampled show increasing O/C ratio and decreasing H/C (hydrogen-to-carbon) ratio with temperature, further indicating that more oxygenated OA components are typically less volatile. Future experiments should systematically explore a wider range of mass concentrations to more fully characterize the volatility distributions of these OAs.

Molecular characterization of nitrogen-containing organic compounds in biomass burning aerosols using high-resolution mass spectrometry

Although nitrogen-containing organic compounds (NOC) are important components of atmospheric aerosols, little is known about their chemical composition. Here we present detailed characterization of the NOC constituents of biomass burning aerosol (BBA) samples using high-resolution electrospray ionization mass spectrometry (ESI/MS). Accurate mass measurements combined with MS/MS fragmentation experiments of selected ions were used to assign molecular structures to individual NOC species. Our results indicate that N-heterocyclic alkaloid compounds (species naturally produced by plants and living organisms) comprise a substantial fraction of NOC in BBA samples collected from test burns of five biomass fuels. High abundance of alkaloids in test burns of ponderosa pine (a widespread tree in the western U.S. areas frequently affected by large scale fires) suggests that N-heterocyclic alkaloids in BBA may play a significant role in dry and wet deposition of fixed nitrogen in this region.