Evaluation of the CAMS reanalysis for atmospheric black carbon and carbon monoxide over the north China plain

Black carbon (BC) and carbon monoxide (CO) at different model levels from the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis were comprehensively evaluated against observations performed simultaneously on both surface and mountain sites in winter and summer in the North China Plain for the first time. CAMS could capture the seasonal difference in BC and CO emission on both sites but showed significant and persistent biases. Biases were high on the surface site and low on the mountain site for both seasons, implying the uncertainties in emission inventories used in the CAMS reanalysis which may have more influence near source. Biases were reduced and the correlation coefficient of CAMS BC with observed BC increased when two datasets were compared on a daily basis, which suggests daily or longer time averaged CAMS BC could be more suitable for trend analysis. Although CAMS could generally reproduce the distinct diurnal variation of BC and CO on both sites, the inaccurate representation of the daily evolution of planetary boundary layer (PBL) in model may bring more uncertainties to the concentration biases on surface from midnight to early morning. BC hydrophilic ratio from CAMS displayed large biases compared to observations with no seasonal difference on both sites, which was probably resulted from the initial emission state of BC hygroscopicity for all source types in model. Uncertainties in the removal processes and the simplified aging processes in model could further induce uncertainty in modelling BC hydrophilic ratio in the CAMS. These results could not only be referenced for the improvement on CAMS reanalysis but also facilitate model or trend analysis of BC and CO pollution by utilizing the CAMS reanalysis product from both short- and long-term perspectives, which will be beneficial to both the mitigation and policy-making on primary emissions in China.

Aerosol mass and size-resolved metal content in urban Bangkok, Thailand

Inhalable particulate matter (PM) is a health concern, and people living in large cities such as Bangkok are exposed to high concentrations. This exposure has been linked to respiratory and cardiac diseases and cancers of the lung and brain. Throughout 2018, PM was measured in northern Bangkok near a toll road (13.87°N, 100.58°E) covering all three seasons (cool, hot and rainy). PM₁₀ was measured in 24- and 72-h samples. On selected dates aerodynamic size and mass distribution were measured as 3-day samples from a fixed 5th floor inlet. Particle number concentration was measured from the 5th floor inlet and in roadside survey measurements. There was a large fraction of particle number concentration in the sub-micron range, which showed the greatest variability compared with larger fractions. Metals associated with combustion sources were most found on the smaller size fraction of particles, which may have implications for associated adverse health outcomes because of the likely location of aerosol deposition in the distal airways of the lung. PM₁₀ samples varied between 30 and 100 μg m^-3, with highest concentrations in the cool season. The largest metal fractions present in the PM₁₀ measurements were calcium, iron and magnesium during the hot season with average airborne concentrations of 13.2, 3.6 and 2.0 μg m^-3, respectively. Copper, zinc, arsenic, selenium, molybdenum, cadmium, antimony and lead had large non-crustal sources. Principal component analysis (PCA) identified likely sources of the metals as crustal minerals, tailpipe exhaust and non-combustion traffic. A health risk analysis showed a higher risk of both carcinogenic and non-carcinogenic health effects in the drier seasons than the wet season due to ingestion of nickel, arsenic, cadmium and lead.

Impact of COVID-19 Pandemic Lockdown in Ambient Concentrations of Aromatic Volatile Organic Compounds in a Metropolitan City of Western India

The real-time Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX) concentrations were measured in a metropolitan city of India during January to May of 2020 and 2014-2015-2018 to assess the impact of emission reduction during the COVID-19 lockdown. The total BTEX (∑BTEX) concentrations were 11.5 ± 9.0, 15.7 ± 16, 5.3 ± 5.0, 2.9 ± 2.0, and 0.93 ± 1.2 ppbv in January-May 2020, respectively. The evening rush hour peaks of BTEX during lockdown decreased by 4-5 times from the same period of years 2014-2015-2018. A significant decline in background concentrations suggests a regional-scale reduction in anthropogenic emissions. The contributions of ∑TEX compounds to ∑BTEX increased from 42% to 59% in winter to 64%-75% during the lockdown under hot summer conditions. While emission reductions dominated during the lockdown period, the meteorological and photochemical factors may also have contributed. Meteorological influence on actual observed BTEX data was removed by normalizing with ventilation coefficient (VC). The actual ambient air reductions of 85%-90% and VC-normalized reductions of 54%-88% of the BTEX concentrations during lockdown were estimated compared to those during the same period of 2014-2015-2018. The estimated changes using nighttime data, which take into account BTEX photooxidation removal, are ∼8% lower than the VC-normalized estimates using all data. These significant reductions in BTEX concentrations are consistent with the change in people's movement as inferred from mobility data during the lockdown. Although enforced, the significant decline in ambient BTEX levels during lockdown was a good change for the air quality. The study suggests a need for more effective science-based policies that consider local and regional factors.

Characteristics and Source Apportionment of Black Carbon (BC) in a Suburban Area of Klang Valley, Malaysia

Black carbon (BC) is of concern due to its contribution to poor air quality and its adverse effects human health. We carried out the first real-time monitoring of BC in Malaysia using an AE33 Aethalometer. Measurements were conducted between 1 January and 31 May 2020 in a university area in a suburban location of the Klang Valley. The measurement period coincided with the implementation of a movement control order (MCO) in response to COVID-19. The mean concentration of BC before the MCO was 2.34 µg/m3 which decreased by 38% to 1.45 µg/m3 during the MCO. The BC is dominated by fossil-fuel sources (mean proportion BCff = 79%). During the MCO, the BCff concentration decreased by more than the BCbb concentration derived from biomass burning. BC and BCff show very strong diurnal cycles, which also show some weekday–weekend differences, with maxima during the night and just before noon, and minima in the afternoon. These patterns indicate strong influences on concentrations from both traffic emissions and boundary layer depth. BC was strongly correlated with NO2 (R = 0.71), another marker of traffic emission, but less strongly with PM2.5 (R = 0.52). The BC absorption Ångström exponent (AAE) ranged between 1.1 and 1.6. We observed pronounced diurnal cycles of lower AAE in daytime, corresponding to BCff contributions from traffic. Average AAE also showed a pronounced increase during the MCO. Our data provides a new reference for BC in suburban Malaysia for the public and policy-makers, and a baseline for future measurements.

Isotope constraints of the strong influence of biomass burning to climate-forcing Black Carbon aerosols over Southeast Asia

Black Carbon (BC) deteriorates air quality and contributes to climate warming, yet its regionally- and seasonally-varying emission sources are poorly constrained. Here we employ natural abundance radiocarbon (¹⁴C) measurements of BC intercepted at a northern Malaysia regional receptor site, Bachok, to quantify the relative biomass vs. fossil source contributions of atmospheric BC, in a first year-round study for SE Asia (December 2015-December 2016). The annual average ¹⁴C signature suggests as large contributions from biomass burning as from fossil fuel combustion. This is similar to findings from analogous measurements at S Asian receptors sites (~50% biomass burning), while E Asia sites are dominated by fossil emission (~20% biomass burning). The ¹⁴C-based source fingerprinting of BC in the dry spring season in SE Asia signals an even more elevated biomass burning contribution (~70% or even higher), presumably from forest, shrub and agricultural fires. This is consistent with this period showing also elevated ratio of organic carbon to BC (up from ~5 to 30) and estimates of BC emissions from satellite fire data. Hence, the present study emphasizes the importance of mitigating dry season vegetation fires in SE Asia.

Spatial variability of sedimentary carbon in South Yellow Sea, China: impact of anthropogenic emission and long-range transportation

During the last few decades, sedimentary carbons gain great concerns of research interest among the scientific committee worldwide due to their adverse impact on aquatic chemistry, ecology, and hence human health along with global climate change. In the present study, we investigated the spatial distribution of mass concentration of sedimentary carbon (viz. black carbon: BC, and its components, char and soot) along with their burial fluxes in the surface sediments of the South Yellow Sea (SYS). The concentration of sedimentary carbon is measured by using an emerging method of thermal/optical reflectance. The observed BC concentration is found in the range of 0.02-1.02 mg g^-1 with a mean value of 0.49 ± 0.26 mg g^-1. The mean burial fluxes of BC, char, and soot also have a similar spatial variation to their concentration with the mean value along with relative standard deviation (in bracket) 22.43 ± 12.49 (~ 56%), 5.90 ± 3.99 (~ 68%), and 16.53 ± 10.67 (65%), respectively. Relatively lower value of char/soot ratio, i.e., 0.48 ± 0.22, indicates the dominance of soot in surface sediments that could be mainly derived from the fossil fuel combustion which is further confirmed from emission inventory data suggesting maximum contribution, i.e., ~ 66-80%, of the total BC emission emitted from residential and industrial emission sources. The back trajectories analysis revealed a significant impact of long-range transportation on BC concentration in the surface sediments of SYS. Further study of BC concentrations in sea sediments and their interaction with other organic/inorganic compounds in continental shelves is highly needed for a better understanding of the global carbon cycle.

Carbonaceous Aerosols Collected at the Observatory of Monte Curcio in the Southern Mediterranean Basin

This work provides the first continuous measurements of carbonaceous aerosol at the Global Atmosphere Watch (GAW) Monte Curcio regional station, within the southern Mediterranean basin. We specifically analyzed elemental carbon (EC) and organic carbon (OC) concentrations in particulate matter (PM) samples, collected from April to December during the two years of 2016 and 2017. The purpose of the study is to understand the behavior of both PM and carbonaceous species, in their fine and coarse size fraction, along with their seasonal variability. Based on 18 months of observations, we obtained a dataset that resulted in a vast range of variability. We found the maximum values in summer, mainly related to the enhanced formation of secondary pollutants owing to intense solar radiation, also due to the high frequency of wildfires in the surrounding areas, as well as to the reduced precipitation and aerosol-wet removal. We otherwise observed the lowest levels during fall, coinciding with well-ventilated conditions, low photochemical activity, higher precipitation amounts, and less frequency of Saharan dust episodes. We employed the HYSPLIT model to identify long-range transport from Saharan desert. We found that the Saharan dust events caused higher concentrations of PM and OC in the coarser size fraction whereas the wildfire events likely influenced the highest PM, OC, and EC concentrations we recorded for the finer fraction.

Exploratory assessment of outdoor and indoor airborne black carbon in different locations of Hanoi, Vietnam

Black carbon (BC) is a significant component of atmospheric particulate matter, especially in areas affected by combustion emissions. Despite the fact that air pollution is a great concern in Vietnam, there are no studies on the level of BC in the outdoor and indoor environment. In this exploratory study, an assessment of urban BC concentrations was conducted through monitoring of both outdoor and indoor BC concentrations in three households and one working office at different locations across Hanoi. PM_2.5 and meteorology data were also obtained for this monitoring period to evaluate the association between them and the outdoor BC concentration. Overall, the mean indoor and mean outdoor BC concentrations by 30 second-logs for the monitoring period were 4.42 μg/m³ and 4.89 μg/m³, respectively. Time-series analysis of paired indoor and outdoor BC concentrations suggested that indoor BC level was usually influenced by outdoor BC level (r = 0.78, p < 0.001). In this study, we observed a significant positive association between outdoor BC and PM_2.5 (r = 0.39, p < 0.001) while outdoor BC negatively correlated with wind speed (r = -0.34, p < 0.001). The level of outdoor BC in Hanoi measured in this study is relatively high and should be confirmed by further studies.

Chemical characterization and quantitativ e assessment of source-specific health risk of trace metals in PM1.0 at a road site of Delhi, India

This study presents the concentration of submicron aerosol (PM_1.0) collected during November, 2009 to March, 2010 at two road sites near the Indian Institute of Technology Delhi campus. In winter, PM_1.0 composed 83% of PM_2.5 indicating the dominance of combustion activity-generated particles. Principal component analysis (PCA) proved secondary aerosol formation as a dominant process in enhancing aerosol concentration at a receptor site along with biomass burning, vehicle exhaust, road dust, engine and tire tear wear, and secondary ammonia. The non-carcinogenic and excess cancer risk for adults and children were estimated for trace element data set available for road site and at elevated site from another parallel work. The decrease in average hazard quotient (HQ) for children and adults was estimated in following order: Mn > Cr > Ni > Pb > Zn > Cu both at road and elevated site. For children, the mean HQs were observed in safe level for Cu, Ni, Zn, and Pb; however, values exceeded safe limit for Cr and Mn at road site. The average highest hazard index values for children and adults were estimated as 22 and 10, respectively, for road site and 7 and 3 for elevated site. The road site average excess cancer risk (ECR) risk of Cr and Ni was close to tolerable limit (10^-4) for adults and it was 13-16 times higher than the safe limit (10^-6) for children. The ECR of Ni for adults and children was 102 and 14 times higher at road site compared to elevated site. Overall, the observed ECR values far exceed the acceptable level.

Ambient particulate matter and carbon monoxide at an urban site of India: Influence of anthropogenic emissions and dust storms

Continuous measurements of PM_2.5, PM₁₀ and CO were conducted at an urban site of Udaipur in India from April 2011 to March 2012. The annual mean concentrations of PM_2.5, PM₁₀ and CO were 42 ± 17 μg m^-3, 114 ± 31 μg m^-3 and 343 ± 136 ppbv, respectively. Concentrations of both particulate and CO showed high values during winter/pre-monsoon (dry) period and lowest in the monsoon season (wet). Local anthropogenic emission and long-range transport from open biomass burning sources along with favourable synoptic meteorology led to elevated levels of pollutants in the dry season. However, higher values of PM₁₀/PM_2.5 ratio during pre-monsoon season were caused by the episodes of dust storm. In the monsoon season, flow of cleaner air, rainfall and negligible emissions from biomass burning resulted in the lowest levels of pollutants. The concentrations of PM_2.5, PM₁₀ and CO showed highest values during morning and evening rush hours, while lowest in the afternoon hours. In winter season, reductions of PM_2.5, CO and PM₁₀ during weekends were highest of 15%, 13% and 9%, respectively. In each season, the highest PM_2.5/PM₁₀ ratio coincided with the highest concentrations of pollutants (CO and NO_X) indicating predominant emissions from anthropogenic sources. Exceptionally high concentrations of PM₁₀ during the episode of dust storm were due to transport from the Arabian Peninsula and Thar Desert. Up to ∼32% enhancements of PM₁₀ were observed during strong dust storms. Relatively low levels of O₃ and NO_x during the storm periods indicate the role of heterogeneous removal.

Sources and mass inventory of sedimentary polycyclic aromatic hydrocarbons in the Gulf of Thailand: Implications for pathways and energy structure in SE Asia

Surface sediments obtained from a matrix of 92 sample sites in the Gulf of Thailand (GOT) were analyzed for a comprehensive study of the distribution, sources, and mass inventory of polycyclic aromatic hydrocarbons (PAHs) to assess their input pathways and impacts of the regional land-based energy structure on the deposition of PAHs on the adjacent continental margins. The concentration of 16 PAHs in the GOT ranged from 2.6 to 78.1ng/g (dry weight), and the mean concentration was 19.4±15.1ng/g. The spatial distribution pattern of 16 PAH was generally consistent with that of sediment grain size, suggesting the influence of regional hydrodynamic conditions. Correlation and principal component analysis of the PAHs indicated that direct land-based inputs were dominantly responsible for the occurrence of PAHs in the upper GOT and the low molecular weight (LMW) PAHs in the coastal region could be from petrogenic sources. A positive matrix factorization (PMF) model apportioned five contributors: petroleum residues (~44%), biomass burning (~13%), vehicular emissions (~11%), coal combustion (~6%), and air-water exchange (~25%). Gas absorption may be a significant external input pathway for the volatile PAHs in the open GOT, which further implies that atmospheric loading could be important for the sink of PAHs in the open sea of the Southeast Asia (SE Asia). The different PAH source patterns obtained and a significant disparity of PAH mass inventory in the sediments along the East and Southeast Asia continental margins can be ascribed mainly to different land-based PAH emission features under the varied regional energy structure in addition to the depositional environment and climatic conditions.

Characteristics of carbonaceous aerosols: Impact of biomass burning and secondary formation in summertime in a rural area of the North China Plain

To determine the characteristics of carbonaceous aerosols in rural areas of the North China Plain, field measurements were conducted at Yucheng (YC) in the summers of 2013 and 2014. The concentrations of carbonaceous aerosols at YC exhibited clear diurnal variation, with higher concentrations in the early morning and at night and lower concentrations during the afternoon hours. The mass-balance method designed for particulate matter smaller than 2.5μm (PM2.5) was used to calculate the organic matter (OM)/organic carbon (OC) ratio. The value obtained, 2.07±0.05, was suggested as a reference to estimate organics in PM2.5 in rural areas of the North China Plain. Biomass burning was identified to be a significant source of carbonaceous aerosols; approximately half of the samples obtained at YC were affected by biomass burning during summer 2013. Case studies revealed that biomass burning accounted for up to 52.6% of the OC and 51.1% of the elemental carbon in PM2.5 samples. The organic coatings observed on sulphur-rich and potassium-rich particles indicated the formation of secondary organic aerosols (SOA) from the oxidation of precursor volatile organic compounds (VOCs) during the aging of smoke released from biomass burning. Based on the evolution of the VOCs, the contribution of VOCs oxidation to SOA concentration was 3.21 and 1.07μgm(-3)ppm(-1) CO under conditions of low nitrogen oxide (NOx) and high NOx, respectively. Aromatics (e.g. benzene, toluene, xylene and ethylbenzene) made the greatest contribution to SOA concentration (88.4% in low-NOx conditions and 80.6% in high-NOx conditions). The results of the study offer novel insights into the effects of biomass burning on the carbonaceous aerosols and SOA formation in polluted rural areas.

Monitoring of black carbon concentration at an inland rural area including fixed sources in Korea

We monitored black carbon (BC) concentration for 6months to understand the characteristics of atmospheric aerosols of an inland rural area in Korea. A multi-angle absorption photometer was used to continuously monitor the BC concentration, which was compared with elemental carbon (EC) concentration measured by an OC/EC Analyzer. For the atmospheric aerosols less than 10μm, size distributions were measured using both an optical particle counter and a scanning mobility particle sizer. The diurnal variations for BC concentration show that the average BC concentration was 1.43μgm(-3) and exhibited peaks in the morning rush hours. However, the BC concentration measured at night from 20:00 to 08:00 was higher than that measured during the day. The reason why the BC concentration at night was higher would be partly due to the regional characteristics influenced by the combination of local fixed sources and traffic condition. It is suggested that the traffic and transporting of pollutants from the west influenced the increase in the BC concentration at inland rural area including fixed sources.

Characterization and sources of black carbon in PM(2.5) at a site close to a roadway in Gwangju, Korea, during winter

Continuous measurements of black carbon (BC) concentrations in PM2.5 were conducted using a single-wavelength aethalometer (@880 nm, Magee Sci., AE16) at a site close to a roadway (∼70 m from roadside) in Gwangju, Korea, during winter (December-February) to investigate the characteristics and sources of BC particles. The BC concentrations ranked in the order of January > December > February, probably due to lower boundary layer height, ambient temperature, and wind speed during January. Diurnal patterns in BC and carbon monoxide (CO) levels exhibited peak concentrations during the morning and evening hours coinciding with rush-hour traffic, with a strong correlation (R(2)) ranging from 0.52 (December) to 0.87 (January). It was found that wind speed was an important factor controlling BC concentrations at the site. Very high BC concentrations, up to ∼18.0 μg m(-3), were observed at wind speeds < 1.5 m s(-1). The BC concentrations acquired under weak wind conditions are highly correlated with CO with ΔBC/ΔCO (the slope of BC and CO correlation) of 0.0063 (R(2) = 0.55, p < 0.01) and 0.0065 (R(2) = 0.59, p < 0.01) μg m(-3) ppbv(-1) during day and night, respectively, suggesting no significant difference in the fraction of diesel vehicles between the daytime and nighttime periods. Two BC episodes, "A" and "B", were classified based on BC, PM2.5, and secondary SO4(2-) concentrations, and discussed to investigate the difference in the evolution of the BC observed. Episode "A" was associated with high BC and low PM2.5 and SO4(2-) concentrations, while episode "B" was associated with high concentrations of BC, PM2.5, and SO4(2-). Based on the temporal profiles of BC, NO, and NOx concentrations, CO/NOx ratio, and potential source contribution function map for BC, the BC observed during episode "A" was mostly attributed to locally produced emissions (e.g., traffic). However, the BC during episode "B" was influenced by long-range transport of air masses from China, as well as the local emissions.

Sources and radiative effects of wintertime black carbon aerosols in an urban atmosphere in east India

We carried out an analysis of black carbon (BC) surface mass concentration, its radiative effects, and sources of origin in an urban atmosphere in east India, during winter season, through ground-based measurements and application of modelling tools. BC surface mass concentration exhibited diurnal variation with their higher values and a larger variability during evening to early morning hours than during daytime (1100-1600 h, Local Time, LT) hours. Daytime mean surface BC mass concentration and BC mass fraction in total aerosol (size range 0.23-20 μm) and in submicronic aerosol (size range 0.23-1 μm) during the study period, corresponding to the well-mixed atmospheric layer were 11 μg m(-3), 3-10%, and 9-16% respectively. The mean BC optical depth (BC-AOD) and BC-AOD fraction at 0.5 μm were estimated in an optical model as 0.11 and 13% respectively. Mean shortwave aerosol radiative forcing due to BC at top-of-atmosphere (TOA) during the study period was found to be +0.94 Wm(-2), which is about 59% the global mean radiative forcing due to carbon-dioxide gases. Estimates from BC simulations in a general circulation model showed BC surface concentration and BC optical depth in east India are primarily attributed to emissions from biofuel and fossil fuel combustion. Most of BC surface concentration (95%) and BC optical depth (60%) are contributed by emissions arising from the Indo-Gangetic plain (IGP) but there is a significant influence to BC columnar loading through elevated transport channels attributed mainly to emissions from open biomass burning from distant regions outside IGP.