Characteristics Of Carbonaceous Aerosols Research Articles

Characteristics of carbonaceous aerosols in four northern Chinese cities during the 2022 Winter Olympics

To study the impact of control measures during the 2022 Winter Olympics on carbonaceous aerosols, samples of fine particulate matter (PM2.5) were collected in Zhangjiakou, Baoding, Shijiazhuang, and Handan in northern China from January to March, 2022. The impacts of different intensities of control measures on organic carbon (OC) and elemental carbon (EC) in the four cities were analyzed. Compared with those in the precontrol period, the decreases in the PM2.5 concentrations in the four cities during the strict control period were ranked in the order of Zhangjiakou (53%), Handan (41%), Shijiazhuang (38%), and Baoding (36%); the decreases in the OC concentrations were ranked in the order of Zhangjiakou (40%), Shijiazhuang (22%), Baoding (21%), and Handan (16%); and the decreases in the EC concentrations were ranked in the order of Zhangjiakou (51%), Baoding (35%), Shijiazhuang (3%), and Handan (−36%). The EC concentration in Handan increased rather than decreased throughout the strict control period. In Zhangjiakou, the reduction in secondary organic carbon (SOC) and primary organic carbon (POC) began notably before the strict control period, whereas in Baoding and Shijiazhuang, it began after the precontrol period. The efficiency of the control measures in lowering SOC was as follows: Baoding (38%), Zhangjiakou (32%), Handan (18%), and Shijiazhuang (12%). SOC formation was influenced by strict control measures that reduced pollution from coal combustion and vehicle exhaust in Zhangjiakou, Baoding, and Shijiazhuang. Conditional probability function (CPF) analysis and potential source contribution factor (PSCF) were used to analyze the potential source regions of EC and OC during the study periods in each city. Transport from Inner Mongolia, Shanxi, the Beijing‒Tianjin‒Hebei region, and northern Henan primarily influenced the presence of EC and OC during the study periods in each city. This study provides theoretical suggestions for cities to optimize their emission control strategies.

Change Characteristics of Carbonaceous Aerosol in Chengdu from 2018 to 2021

Carbonaceous aerosol is an important component of atmospheric fine particulates （PM2.5） that has an important effect on global climate change, atmospheric visibility, regional air quality, and human health. In order to investigate the long-term change characteristics of carbonaceous aerosols under the background of emission reduction, the concentrations of organic carbon （OC）, elemental carbon （EC） in PM2.5 samples, and volatile organic compounds （VOCs） in Chengdu from 2018 to 2021 and the corresponding meteorological factors were obtained through real-time online monitoring. The results showed that the average ρ（OC） and ρ（EC） during the monitoring period were （10.9 ±5.7） μg·m-3 and （2.6 ±1.9） μg·m-3, accounting for 25.2% and 6.0% of PM2.5, respectively, and the average ρ（SOC） was （5.7 ±3.3） μg·m-3, accounting for 52.9% of OC. The concentrations of OC, EC, and PM2.5 showed a downward trend from 2018 to 2020 [PM2.5： The concentration of average annual decrease was -7.1 μg·（m3·a） -1, with an average annual decrease of -14.6 %·a-1； OC： -1.7 μg·（m3·a）-1, -14.2 %·a-1； EC： -0.1 μg·（m3·a）-1, -4.4 %·a-1], and the concentrations of each pollutant in 2021 rebounded in different ranges compared with those in 2020. The concentrations of PM2.5 and OC were as follows： winter > spring > autumn > summer, and the concentrations of EC were as follows： winter > autumn > spring > summer. The proportions of OC and EC were higher in summer and autumn than in other seasons, with the average proportions of 26.8% and 6.9%, respectively. With the aggravation of the pollution level, OC, EC, and SOC concentrations gradually increased, but the proportions in PM2.5 showed a gradual downtrend, indicating that the control factor of PM2.5 pollution in Chengdu was not the carbon component. Source apportionment results showed that carbonaceous aerosols in Chengdu were mainly affected by motor vehicles, industrial sources, biomass combustion sources, and VOCs secondary reaction. From 2019 to 2021, EC was affected by the characteristic components of motor vehicles and decreased yearly. OC and EC were affected by VOCs more in spring and autumn than in other seasons. VOCs emission management should be increased in spring and autumn to reduce the impact of secondary reaction.

Characteristics of PM2.5 bounded carbonaceous aerosols, carbon dioxide and its stable carbon isotopes (δ13C) in rural households in northwest China: Effect of different fuel combustion

In order to fully understand the carbon emission from different fuels in rural villages of China, especially in the typical atmospheric pollution areas. The characteristics of carbonaceous aerosols and carbon dioxide (CO2) with its stable carbon isotope (δ13C) were investigated in six households, which two households used coal, two households used wood as well as two households used biogas and liquefied petroleum gas (LPG), from two rural villages in Fenwei Plain from March to April 2021. It showed that the fine particulate matter (PM2.5) emitted from biogas and LPG couldn't be as lower as expected in this area. However, the clean fuels could relatively reduce the emissions of organic carbon (OC) and element carbon (EC) in PM2.5 compare to the solid fuels. The pyrolyzed carbon (OP) accounted more total carbon (TC) in coal than the other fuels use households, indicating that more water-soluble OC existed, and it still had the highest secondary organic carbon (SOC) than the other fuels. Meantime, the coal combustions in the two villages had the highest CO2 concentration of 527.6 ppm and 1120.6 ppm, respectively, while the clean fuels could effectively reduce it. The average δ13C values (−26.9‰) was much lighter than almost all the outdoor monitoring and similar to the δ13C values for coal combustion and vehicle emission, showing that they might be the main contributors of the regional atmospheric aerosol in this area. During the sandstorm, the indoor PM2.5 mass and CO2 were increasing obviously. The indoor cancer risk of PAHs for adults and children were greater than 1 × 10−6, exert a potential carcinogenic risk to human of solid fuels combustion in rural northern China. It is important to continue concern the solid fuel combustion and its health impact in rural areas.

Characterization and apportionment of carbonaceous aerosol emission factors from light-duty and heavy-duty vehicle fleets in Maharashtra, India

This study aims to investigate the characteristics of carbonaceous aerosols and estimate emission factor (EF) based on roadway tunnel measurements, from two distinct vehicular fleets: an all light-duty vehicle (LDV) fleet, and a mixed fleet of 80% LDV and 20% heavy-duty vehicle (HDV). Carbonaceous content (organic carbon: OC and elemental carbon: EC) in total fine particles (PM2.5) accounted for 41% ± 6.8% in LDV fleet and 48% ± 7.2% in mixed fleet. While higher volatile OC dominated in the LDV fleet emissions, in mixed fleet, lower volatile OC and EC emissions dominated due to the presence of higher HDV and super-emitter (SE) fractions which led to significantly higher optically active absorbing aerosols. Reconstructed HDV fleet EF was higher than LDV fleet by 36 times (PM2.5), 19 times (OC) and 51 times (EC). Our findings emphasize the significance of implementing vehicle inspection and maintenance programs, coupled with decarbonization of HDVs to mitigate on-road vehicular emissions in India.

Sources of atmospheric light-absorbing fine aerosols: Insights from optical source apportionment utilizing measurements made during COVID-19 lockdowns at a COALESCE network site - Bhopal, India

The source-related optical characteristics of carbonaceous aerosols which absorb light are not well-known as they can be generated by a variety of sources. In this study, specific source-related optical properties of carbonaceous aerosols and mineral dust were investigated using a two-year dataset of absorption at multiple wavelengths and chemical species measured at Bhopal, India. A receptor model (Positive Matrix Factorization PMF5) was applied to the combined dataset to achieve optical source apportionment of carbonaceous aerosols and mineral dust. PMF resolved six factors accounting for carbonaceous aerosols and dust particulate matter (CDPM), which were identified as coal combustion, traffic exhaust, biomass burning, mineral dust, industry, and secondary organic aerosol (SOA) factors. The average contributions of these factors to the total CDPM mass were 29 % (coal combustion), 20 % (SOA), 16 % (traffic exhaust), 15 % (industry), 14 % (biomass burning), and 6 % (mineral dust (MD)) during the study period. The dominant contributors (at 405 nm) to aerosol light absorption were coal combustion (33 %), traffic exhaust (30 %), and biomass burning (29 %) factors. Specific source-related absorption Ångström exponent (AAE) values indicated that black carbon (BC) was the dominant light absorber in the coal and traffic emission factors. However, brown carbon (BrC) was present in the biomass-burning emissions. The specific source-related mass absorption cross section (MAC) for BC from coal combustion was higher at 635 nm than for MACBC from biomass burning, industry, and traffic exhaust factors. Overall, this study helped in the identification of additional light-absorbing sources of CDPM such as MD and SOA, and differentiate between optical parameters (AAE and MAC) of light-absorbing species in these sources.

Temporal variations, sources, and regional transport of carbonaceous species in PM2.5 in a northern China city: the role of domestic heating

Domestic heating is an important source of carbonaceous aerosols in northern China in winter. The seasonal variations, sources, and regional transport of carbonaceous species in PM2.5 in Yuncheng in the winter and summer of 2020–2021 were investigated in this study, with a particular focus on the role of domestic heating. Meanwhile, the pollution characteristics of carbonaceous aerosols in Beijing in winter were also investigated for comparison. The mass concentrations of organic carbon (OC) and elemental carbon (EC) and their contributions to PM2.5 were significantly enhanced during the heating period compared to other sampling periods in Yuncheng, however, no obvious differences were observed before and during the heating periods in Beijing. Source apportionment results showed that the heating related emission (50.9%) was the dominant source of total carbon in Yuncheng in the heating period, while vehicular emission (49.6%) was dominant in summer. Combing the positive matrix factorization (PMF) and potential source contribution function (PSCF) analysis, it was concluded that both local and regional heating activities contributed highly to carbonaceous aerosols in Yuncheng. It would be therefore of great environmental benefits to promote the clean residential heating transition in Yuncheng and other similar cities.Graphical

Geochemical characteristics and socioeconomic associations of carbonaceous aerosols in coal-fueled cities with significant seasonal pollution pattern

Carbonaceous aerosols, comprising organic carbon (OC) and elemental carbon (EC), are critical component of fine particulate matter (PM2.5), with diverse impacts on air quality and human health. This study investigated the concentrations and seasonal patterns of carbonaceous species in PM2.5 during both the heating season (January 2021) and non-heating season (July 2021) in three coal-fueled cities in northern China, as well as the differences in carbonaceous aerosols and their associations with socioeconomic parameters in cities situated on either side of the “Hu Line” in China. The results showed that, owing to intensified coal combustion and unfavorable meteorological conditions, levels of OC, EC, and OC/EC ratios were higher in winter compared to summer. Moreover, the presence of dust (DU) and light pollution (LP) days resulted in elevated OC levels but decreased EC levels. The Char-EC/Soot-EC ratios were highest during LP, followed by CL and DU. A source apportionment analysis demonstrated that coal burning, vehicle exhaust, road dust, and biomass burning were the primary contributors to carbonaceous aerosols, as confirmed by diagnostic ratios, Char-EC/Soot-EC ratios, and PCA analysis. Furthermore, our study found that carbonaceous aerosols concentrations and source apportionment primarily varied with diurnal and seasonal trends and different pollution types. Additionally, at the national scale, population density and urban green space exhibited a positive correlation with OC/EC ratios (p < 0.05), while energy consumption per unit of GDP showed a negative correlation (p < 0.05). The observation that OC/EC ratios were lower in coal-fueled cities than in economy-based cities suggests a more severe pollution scenario. These findings highlight the importance of comprehending of the seasonal variation and chemical characteristics of carbonaceous aerosol for understanding air pollution sources and characteristics, which is essential for both air quality management and human health.

Characteristics of Air Pollutant Distribution and Sources in the East China Sea and the Yellow Sea in Spring Based on Multiple Observation Methods

The composition of marine aerosol is quite complex, and its sources are diverse. Across the East China Sea (ECS) and the Yellow Sea (YS), multi-dimensional analysis of marine aerosols was conducted. The characteristics of carbonaceous aerosols and gaseous pollutants were explored through in situ ship-based observation, MERRA-2 reanalysis datasets and TROPOMI data from Sentinel-5P satellite. Black carbon (BC)’s average concentration is 1.35 ± 0.78 μg/m3, with high-value BC observed during the cruise. Through HYSPLIT trajectory analysis, sources of BC were from the northern Eurasian continent, the Shandong Peninsula, the ECS and Northwest Pacific Ocean (NWPO). The transport of marine sources like ship emissions cannot be ignored. According to the absorption Angstrom exponent (AAE), BC originates from biomass burning (BB) in the shortwave band (~370 nm) and from fossil fuel combustion in the longwave band (~660 nm). Organic carbon (OC), sulfate (SO42−) and BC report higher Angstrom exponent (AE) while dust and sea salt reveal lower AE, which can be utilized to classify the aerosols as being fine- or coarse-mode, respectively. OC has the highest AE (ECS: 1.98, YS: 2.01), indicating that anthropogenic activities could be a significant source. The process of biomass burning aerosol (BBA) mixed with sea salt could contribute to the decline in BBA’s AE. Ship emissions may affect the distribution of tropospheric nitrogen dioxide (NO2) in the ECS, especially during the COVID-19 pandemic. Tropospheric NO2 over the YS has the highest value (up to 12 × 1015 molec/cm2). Stratospheric NO2 has a ladder-like distribution from north to south, and the variation gradient was lower than that in the troposphere. Carbon monoxide (CO) accumulates in the south and east of the ECS and the east of the YS, while the variation over the eastern YS is relatively frequent. Seas near the Korean Peninsula have extremely high CO concentration (up to 1.35 × 1017 molec/cm2).

Highly Time-Resolved Apportionment of Carbonaceous Aerosols from Wildfire Using the TC-BC Method: Camp Fire 2018 Case Study.

The Camp Fire was one of California's deadliest and most destructive wildfires, and its widespread smoke threatened human health over a large area in Northern California in November 2018. To analyze the Camp Fire influence on air quality on a 200 km distant site in Berkeley, highly time-resolved total carbon (TC), black carbon (BC), and organic carbon (OC) were measured using the Carbonaceous Aerosol Speciation System (CASS, Aerosol Magee Scientific), comprising two instruments, a Total Carbon Analyzer TCA08 in tandem with an Aethalometer AE33. During the period when the air quality was affected by wildfire smoke, the BC concentrations increased four times above the typical air pollution level presented in Berkeley before and after the event, and the OC increased approximately ten times. High-time-resolution measurements allow us to study the aging of OC and investigate how the characteristics of carbonaceous aerosols evolve over the course of the fire event. A higher fraction of secondary carbonaceous aerosols was observed in the later phase of the fire. At the same time, the amount of light-absorbing organic aerosol (brown carbon) declined with time.

Emission Characteristics of Organic Carbon and Elemental Carbon in PM10 and PM2.5 from Vehicle Exhaust and Civil Combustion Fuels

To study the emission characteristics of carbonaceous aerosol in particulate matter emitted from vehicle exhaust and main civil combustion fuels, organic carbon (OC) and elemental carbon (EC) in PM10 and PM2.5 samples from vehicle sources (gasoline vehicles, light duty diesel vehicles, and heavy duty diesel vehicles), civil coal (chunk coal and briquette coal), and biomass fuels (wheat straw, wood plank, and grape branches) were collected and analyzed by using a multifunctional portable dilution channel sampler and the Model 5L-NDIR OC/EC analyzer. The results showed that there were significant differences in the proportion of carbonaceous aerosols in PM10 and PM2.5from different emission sources. The proportions of total carbon (TC) in PM10 and PM2.5 of different emission sources were 40.8%-68.5% and 30.5%-70.9%, respectively, and the OC/EC were 1.49-31.56 and 1.90-87.57, respectively. The carbon components produced by different emission sources were dominated by OC, and the OC/TC values in PM10 and PM2.5 were 56.3%-97.0% and 65.0%-98.7%, respectively. The proportions of OC in carbonaceous aerosols in PM10and PM2.5 were in the descending order of:briquette coal>chunk coal>gasoline vehicle>wood plank>wheat straw>light duty diesel vehicle>heavy duty diesel vehicle and briquette coal>gasoline car>grape branches>chunk coal>light duty diesel vehicle>heavy duty diesel vehicle, respectively. The main components of carbonaceous aerosols in PM10 and PM2.5 emitted from the various emission sources were different, and source apportionment of carbonaceous aerosols could be accurately distinguished by their ingredient composition profiles.

Distribution characteristics and optical properties of carbonaceous aerosol: brown carbon and black carbon in Nanchang, inland China

PM2.5 samples were collected from October 31, 2019, to November 10, 2019, in Nanchang for 10 consecutive days. The mass concentrations of PM2.5 and carbon components were measured, and the distribution characteristics of carbonaceous aerosols were discussed. The optical properties of carbonaceous aerosols were quantified by the thermal-optical method and solvent extraction method, respectively. The results showed that the average concentrations of organic carbon (OC) and elemental carbon (EC) in aerosols in Nanchang were 11.79 ± 3.86 and 3.51 ± 1.59 μg m−3, respectively. The average OC/EC was 3.62, and OC2, OC3, OC4 and EC1 accounted for relatively large proportions (19.55, 24.96, 22.37 and 17.38%). Carbonaceous aerosols in Nanchang were greatly affected by coal combustion, vehicle exhaust emissions and secondary organic carbon (SOC) formation. For particulate brown carbon (BrC), the average light absorption coefficient (babs) and mass absorption efficiency (MAE) at 405 nm were 16.87 Mm−1 and 1.49 m2g−1, respectively. The average Absorption Ångström exponent (AAE) was 8.58. For water-soluble organic carbon (WSOC) and methanol-soluble organic carbon (MSOC), the average babs,365,WSOC and babs,365,MSOC were 14.79 and 22.51 Mm−1, respectively. The mean values of AAE300-600,WSOC and AAE300-600,MSOC were 4.17 and 4.84, respectively. The mean MAE365,WSOC and MAE365,MSOC were 1.83 and 2.18 m2 g−1, respectively. The mean value of MAEBC at 405 nm was 10.28 m2 g−1. The optical properties of particulate BrC and dissolved BrC were similar at 405 nm. The light absorption of BrC cannot be ignored, although BC was the main light absorption component.

Carbonaceous aerosols in Lvliang, China: seasonal variation, spatial distribution and source apportionment

Environmental context Lvliang, one of the main cities on the Fenwei Plain, is a key atmospheric pollution prevention area in China. Identification of sources of aerosols is essential to improving environmental air quality in this region. The quantitative source apportionment of carbonaceous aerosols performed in this study provides a better understanding of their sources and implications for climate and air-quality management policies in the Fenwei plain. Rationale Organic carbon (OC) and elemental carbon (EC) are major components of fine particulate matter (PM2.5), and they are of concern due to their significant impacts on human health and climate. Methodology PM2.5 samples were collected daily during four consecutive seasons from 2018 to 2019. This paper highlights the seasonal variations, sources and transport characteristics of carbonaceous aerosol in Lvliang, China. Results The OC and EC concentrations exhibited strong seasonal variations, with the highest in winter, mainly due to high pollution caused by winter heating in northern cities, and secondary OC (SOC) contribution. The average OC/EC ratio (1.72) in Lvliang was lower than those in most regions in China, further indicating that this region was greatly affected by primary source emissions. The highest SOC/OC ratio in summer (25.3%) was due to the positive correlation between SOC and temperature. Through the positive matrix factorisation (PMF) model, four sources of carbonaceous aerosols were identified: vehicle emissions (31.26%), coal combustion (30.83%), biomass combustion (24.36%) and dust emissions (13.55%). Potential source contribution function (PSCF) results indicated that in addition to the impact of local emissions, coal emissions from Ningxia and Shaanxi, motor vehicle emissions and biomass from Inner Mongolia and Ningxia and dust from Shaanxi and Henan Provinces were the major contributors to pollution. Discussion These data provide key information for formulating emission reduction policies and improving air quality on the Fenwei Plain and highlights the urgent need for inter-regional prevention and control measures for the cities in Lvliang.

Impacts of severe residential wood burning on atmospheric processing, water-soluble organic aerosol and light absorption, in an inland city of Southeastern Europe

This study examines the concentrations and characteristics of carbonaceous aerosols (including saccharides) and inorganic species measured by PM2.5 filter sampling and a multi-wavelength Aethalometer during two campaigns in a mountainous, medium-sized, Greek city (Ioannina). The first campaign was conducted in summer and used as a baseline of low concentrations, while the second took place in winter under intensive residential wood burning (RWB) emissions. Very high winter-mean OC concentrations (26.0 μg m−3) were observed, associated with an OC/EC ratio of 9.9, and mean BCwb and PM2.5 levels of 4.5 μg m−3 and 57.5 μg m−3, respectively. Simultaneously, record-high levoglucosan (Lev) concentrations (mean: 6.0 μg m−3; max: 15.9 μg m−3) were measured, revealing a severely biomass burning (BB)-laden environment. The water-soluble OC component (WSOC) accounted for 56 ± 9% of OC in winter, exhibiting high correlations (R2 = 0.93–0.97) with BB tracers (nss-K+, BCwb, Lev), nitrate and light absorption, potentially indicating the formation of water-soluble brown carbon (BrC) from fast oxidation processes. The examination of diagnostic ratios involving BB tracers indicated the prevalence of hardwood burning, while the mean Lev/OC ratio (22%) was remarkably higher than literature values. Applying a mono-tracer method based on levoglucosan, we estimated very high BB contributions to OC (∼92%), EC (∼64%) and WSOC (∼87%) during winter. On the contrary, low levels were registered during summer for all carbonaceous components, with winter/summer ratios of 4–5 for PM2.5 and BC, 10 for OC, 30 for BCwb and ∼1100 for levoglucosan. The absence of local BB sources in summer, combined with the photochemical processing and aging of regional organic aerosols, resulted in higher WSOC/OC fractions (64 ± 13%). The results indicate highly soluble fine carbonaceous aerosol fraction year-round, which when considered alongside the extreme concentration levels in winter can have important implications for short- and long-term health effects.

Characteristics and source origins of carbonaceous aerosol in fine particulate matter in a megacity, Sichuan Basin, southwestern China

This paper reports the temporal variations, sources and transport characteristics of carbonaceous aerosol in Chongqing, a megacity in the Sichuan Basin. Hourly organic carbon (OC) and elemental carbon (EC) mass concentrations in PM2.5 were measured at an urban supersite from November 2019 to October 2020. The annual mean PM2.5, OC and EC concentrations (±1SD) were 38.50 ± 25.79 μg/m3, 9.03 ± 5.73 and 2.45 ± 1.47 μgC/m3, respectively. An intensive influence of biomass combustion was found during the observation period. Strong seasonality of carbonaceous aerosol with highest concentrations in winter and lowest concentrations in summer was observed. Meanwhile, two diverse pathways for secondary formation dominated in different seasons. One was highly related to gas-phase photochemical oxidation under high temperature and radiation, and another was highly related to heterogeneous reactions, while the latter was more significant, especially in winter. Diurnal and quarterly variation patterns for carbonaceous aerosol showed that the development of planetary boundary layer strongly influenced carbonaceous aerosol concentrations. Moreover, the regional sources from the northeast within the basin were identified as major contributors of the primary carbonaceous aerosol to Chongqing, while secondary components were more from local sources than regional transport. This study highlights the importance of prioritising the abatement of gaseous precursors for carbonaceous aerosol and an urgent need for the inter-regional prevention and control measures of the cities located in the Sichuan basin, especially the cities in the northeast of urban Chongqing.

Insight into the characteristics of carbonaceous aerosols at urban and regional sites in the downwind area of Pearl River Delta region, China.

Carbonaceous aerosols (CAs) take up a substantial fraction of fine particle (PM2.5) in the atmosphere, yet high temporal resolution and seasonal variations of their emission sources and formation mechanisms are still poorly characterized in the regions with strong anthropogenic activities. In this study, the spatiotemporal characteristics of CAs and their subfractions, i.e., organic carbon (OC) and elemental carbon (EC), were studied in one of China's key city clusters, the Pearl River Delta (PRD) region. Results show that the annual mean OC and EC concentrations are 5.89±3.32μg/m3 and 1.60±1.00μg/m3 at the urban site, respectively. Such levels are consistently higher than those at the regional site (4.94±3.34μg/m3 of OC and 1.45±0.82μg/m3 of EC), suggesting the strong impact of human activities on OC and EC concentration. Moreover, the OC concentration peak sharply appears at 19:00 across all seasons at the urban site due to the direct influence of traffic exhaust and cooking activities. At regional site, OC peaks in fall afternoon due to intensive photochemical reactions derived combustion-related secondary organic carbon (SOCcom) contributions to the downwind PRD region. Correlations between SOCcom and influence factors were found at both regional and urban sites, suggesting that SOCcom formation is more regionally homogenous and mainly originates from the Zhaoqing-Foshan-Jiangmen belt. In addition, there are significantly different formation mechanisms of non-combustion-related secondary organic carbon (SOCnon-com) in the downwind PRD region. This study provides a solid evidence for collaborative efforts in the mitigation of secondary aerosols in the PRD region.

Characteristics of carbonaceous aerosols in ambient PM2.5 during the COVID-19 period in Nanjing

In order to explore the variations of carbon components[including organic carbon (OC) and element carbon (EC)] in PM2.5 at the urban area of Nanjing during the breakout of COVID-19 period, PM2.5, OC and EC mass concentrations were measured by online monitoring from January to February 2020. Compared to the concentrations before the emergency response, the PM2.5 concentration after the emergency response was reduced by 41.2% and EC reduced by 57.9%. These results indicate that the shutdown significantly reduced PM2.5 and EC concentrations, but the OC concentration increased. Before the emergency response, the OC and EC concentrations were low in daytime and high at night and early morning. After the emergency response, the average concentration of EC only had a slight change within a day and maintained at low concentration level, OC showed a curve trend which was higher in the afternoon and lower in morning and evening. The significant decrease of PM2.5 concentration after the emergency response period led to the increasing of light radiation intensity, which promoted the formation of secondary organic carbon (SOC). The SOC concentration increased when the PM2.5 and EC concentrations decreased, and the correlation between OC and EC also decreased significantly. © 2021, China Environmental Science Press. All rights reserved.

Influence of Meteorological Conditions and Fire Hotspots on PM0.1 in Northern Thailand during Strong Haze Episodes and Carbonaceous Aerosol Characterization

ABSTRACT Northern Thailand has long been severely affected by haze from biomass burning containing fine and ultrafine aerosols in the dry period. The carbonaceous PM0.1 comprising elemental carbon (EC) and organic carbon (OC) collected during the haze and non-haze periods in Chiang Mai, Thailand was investigated. The PM0.1 levels during the haze periods were about 3 times higher than the non-haze periods, a significant increase. PM0.1 concentration was strongly correlated with atmospheric relative humidity and the number of forest fire hotspots. Carbonaceous aerosol characteristics in PM0.1 were analyzed with the thermal/optical transmittance (TOT) method following the IMPROVE protocol. The concentrations of OC and EC, distribution of OC and EC and OC/EC ratios in PM0.1 were evaluated. Average OC and EC mass concentrations in PM0.1 were 6.8 ± 2.7 and 1.4 ± 0.5 µg m–3 during the haze periods, significantly higher than those during the non-haze periods; 1.9 ± 0.9 and 0.5 ± 0.2 µg m–3. The OC/EC ratio increased linearly with the number of hotspots. This indicated significant contribution from biomass burning to the PM0.1. This was strongly supported by the 48-hr backward trajectory simulation, that indicated both domestic and transboundary aerosol transports. Because both organic and elemental carbon are the light-absorbing carbonaceous aerosols, the increase during the haze periods contributed to regional air quality and climate. This study enhances the understanding of PM0.1 behavior in Chiang Mai, Thailand, during the haze periods in upper southeast Asia.

Characteristics of carbonaceous aerosols derived from long-term high-resolution measurements at a high-altitude site in the central Himalayas: radiative forcing estimates and role of meteorology and biomass burning.

Simultaneous observations (2014-2017) of organic carbon (OC) and elemental carbon (EC) are made over a high-altitude site (Nainital, 29.4°N, 79.5°E, 1958m a.m.s.l) in the central Himalayas, and the role of long-range transport, meteorology and biomass burning is studied. There are only a few online and simultaneous observations of OC and EC over South Asia and none in the high-altitude Himalayan region. This work presents the first diurnal variations with a unimodal pattern in both OC and EC at the Himalayan site. Such a diurnal pattern is in contrast with the bimodal pattern observed at any continental polluted site. Clear seasonal variations in OC and EC were seen with a primary maximum during spring and a secondary maximum in autumn/winter. OC and EC concentrations are observed to be as high as 65.8μg/m3 and 12μg/m3, in May, respectively. Concentration weighted trajectory (CWT)-assisted analysis shows that the biomass burning in northern India is one of the major sources for the springtime maximum even at this high-altitude site. The coinciding rise in OC/EC ratio from 4.6 to 7.9, along with fire events, further convinces that the enhancement in the concentrations is due to the biomass burning at distant regions and long-range transport of air masses influencing this high-altitude site. A poor covariation between OC-EC and the boundary-layer height during autumn and winter suggests that secondary maxima in OC and EC are most likely due to local sources, e.g. household burning for heating during this cold period when the temperature drops sharply after October and remains low until February. The higher temporal resolution of online measurements reveals that swiftly varying meteorological parameters change the OC-EC concentrations at diurnal scales. Back-air trajectory-assisted analysis of residence time and its relationship with OC and EC confirms the increase in their concentration in slow-moving air masses. The observed diurnal variations of EC are utilized to estimate the radiative forcing and shown that the atmospheric radiative forcing during the afternoon is about 70% higher than the forenoon one. It is envisaged that this dataset with diurnal observations of OC and EC would be an important input for studying the radiation budget and source apportionment over this high-altitude region.

Absorption and radiative characteristics of brown carbon aerosols during crop residue burning in the source region of Indo-Gangetic Plain

The north-western Indo-Gangetic Plain (IGP) experiences massive crop-residue burning (viz. paddy and wheat) on an annual and seasonal basis. The long-range transport of the particulates emitted from paddy- and wheat-residue burning (expressed as PRB and WRB, respectively) degrades the air quality, perturb the radiative budget, and alter the atmospheric chemistry of downwind IGP locations. Therefore, chemical, absorption and radiative characteristics of carbonaceous aerosols (total carbon; TC) were explored in this study. The fraction of TC in ambient PM2.5 (particulates with aerodynamic diameter ≤ 2.5 μm) was ~45% during PRB and ~24% during WRB. However, biomass burning emissions were the predominant source of TC during both PRB and WRB. The brown carbon (BrC) aerosols at Beas were ~2–3 times more abundant during PRB than in WRB. However, the absorption properties such as mass absorption efficiency and imaginary component of the refractive index for BrC at 405 nm (expressed as MAEBrC-405, kBrC-405, respectively) and radiative characteristics such as light absorption capacity were similar during both PRB and WRB. The similarity between these absorption and radiative characteristics indicate that BrC aerosols emitted during the burning of different biomass may depend only on their combustion condition. Further, the increased biomass burning emissions were linked with enhancement in the light absorption capacity of BrC during PRB. A similar light absorption capacity was observed (~30 W/g) for water-soluble BrC (WS-BrC) and total BrC during PRB. Moreover, the % contribution of BrC and EC to their total direct radiative forcing (DRFTC) during PRB and WRB (~40% and ~60% for BrC and EC, respectively) were also similar. The WS-BrC constitutes only ~15% of DRFTC during PRB. This difference signifies that non-WS-BrC aerosols were the predominant light-absorbing species during PRB (compared to WS-BrC), which needs to be factored into global climate models to mitigate uncertainties.

Effects of coal types and combustion conditions on carbonaceous aerosols in flue gas and their light absorption properties

Under typical Chinese wintry rural conditions, dominating individual coal heating would emit lots of the fine fraction of ambient aerosol exclusively including carbonaceous particulate matter. In this study, a specified drop tube furnace system is employed to simulate experimentally particle matter emitted during individual coal combustion. Emphatically, the effects of coal types, oxygen concentration and combustion ambient on the formation characteristics of carbonaceous aerosols in the flue gas were discussed. It was found that the fraction of organic carbon (OC) and elemental carbon (EC) in the flue gas produced by bituminous coal combustion was lower than that of lignite. Meanwhile, with the increase of oxygen concentration, the production of OC and EC decreased, but the sensitivity of EC to oxygen concentration was higher than that of OC, which indicated that the formation mechanism of OC and EC is extremely different. Noticeable, the Absorption Ångström Exponent (AAE) of methanol-soluble organic carbon (MSOC) is higher than that of water-soluble organic carbon (WSOC), which indicates that a large amount of methanol-soluble but water-insoluble brown carbon has strong light absorption capacity between 330 nm and 550 nm, and its light absorption capacity tends to be in the short-wave region. The mass absorption efficiency (MAE) of brown carbon produced by coal combustion (0.1–1 m2/gC) is similar to that of atmospheric aerosol (0.3–1.8 m2/gC), which indicates that the contribution of brown carbon emitted from coal combustion to the light absorption capacity of atmospheric aerosol should not be underestimated.