Characteristics Of Carbonaceous Aerosols Research Articles

Severe air pollution and characteristics of light-absorbing particles in a typical rural area of the Indo-Gangetic Plain

Total suspended particles (TSP) were collected in Lumbini from April 2013 to March 2016 to better understand the characteristics of carbonaceous aerosol (CA) concentrations, compositions and sources and their light absorption properties in rural region of severe polluted Indo-Gangetic Plain (IGP). Extremely high TSP (203.9 ± 109.6μgm-3), organic carbon (OC 32.1 ± 21.7μgm-3), elemental carbon (EC 6.44 ± 3.17μgm-3) concentrations were observed in Lumbini particularly during winter and post-monsoon seasons, reflecting the combined influences of emission sources and weather conditions. SO42- (7.34 ± 4.39μgm-3) and Ca2+ (5.46 ± 5.20μgm-3) were the most dominant anion and cation in TSP. These components were comparable to those observed in urban areas in South and East Asia but significantly higher than those in remote regions over the Himalayas and Tibetan Plateau, suggesting severe air pollution in the study region. Various combustion activities including industry, vehicle emission, and biomass burning are the main reasons for high pollutant concentrations. The variation of OC/EC ratio further suggested that biomass such as agro-residue burning contributed a lot for CA, particularly during the non-monsoon season. The average mass absorption cross-section of EC (MACEC) and water-soluble organic carbon (MACWSOC) were 7.58 ± 3.39 and 1.52 ± 0.41m2g-1, respectively, indicating that CA in Lumbini was mainly affected by local emissions. Increased biomass burning decreased MACEC; whereas, it could result in high MACWSOC during the non-monsoon season. Furthermore, dust is one important factor causing higher MACWSOC during the pre-monsoon season.

Seasonality of carbonaceous aerosol composition and light absorption properties in Karachi, Pakistan

Characteristics of carbonaceous aerosol (CA) and its light absorption properties are limited in Karachi, which is one of the most polluted metropolitan cities in South Asia. This study presents a comprehensive measurement of seasonality of CA compositions and mass absorption cross-section (MAC) of elemental carbon (EC) and water-soluble organic carbon (WSOC) in total suspended particles (TSP) collected from February 2015 to March 2017 in the southwest part of Karachi. The average TSP, organic carbon (OC), and EC concentrations were extremely high with values as 391.0 ± 217.0, 37.2 ± 28.0, and 8.53 ± 6.97 μg/m3, respectively. These components showed clear seasonal variations with high concentrations occurring during fall and winter followed by spring and summer. SO42−, NO3−, K+, and NH4+ showed similar variations with CA, implying the significant influence on atmospheric pollutants from anthropogenic activities. Relatively lower OC/EC ratio (4.20 ± 2.50) compared with remote regions further indicates fossil fuel combustion as a primary source of CA. Meanwhile, sea salt and soil dust are important contribution sources for TSP. The average MAC of EC (632 nm) and WSOC (365 nm) were 6.56 ± 2.70 and 0.97 ± 0.37 m2/g, respectively. MACEC is comparable to that in urban areas but lower than that in remote regions, indicating the significant influence of local emissions. MACWSOC showed opposite distribution with EC, further suggesting that OC was significantly affected by local fossil fuel combustion. In addition, dust might be an important factor increasing MACWSOC particularly during spring and summer.

Carbonaceous aerosol characteristics on the Third Pole: A primary study based on the Atmospheric Pollution and Cryospheric Change (APCC) network

Carbonaceous aerosols (CAs) scatter and absorb incident solar radiation in the atmosphere, thereby influencing the regional climate and hydrological cycle, particularly in the Third Pole (TP). Here, we present the characteristics of CAs at 19 observation stations from the Atmospheric Pollution and Cryospheric Change network to obtain a deep understanding of pollutant status in the TP. The organic carbon (OC) and elemental carbon (EC) concentrations decreased noticeably inwards from outside to inland of the TP, consistent with their emission load and also affected by transport process and meteorological condition. Urban areas, such as Kathmandu, Karachi, and Mardan, exhibited extremely high OC and EC concentrations, with low and high values occurring in the monsoon and non-monsoon seasons, respectively. However, remote regions inland the TP (e.g., Nam Co and Ngari) demonstrated much lower OC and EC concentrations. Different seasonal variations were observed between the southern and northern parts of the TP, suggesting differences in the patterns of pollutant sources and in distance from the sources between the two regions. In addition to the influence of long-range transported pollutants from the Indo-Gangetic Plain (IGP), the TP was affected by local emissions (e.g., biomass burning). The OC/EC ratio also suggested that biomass burning was prevalent in the center TP, whereas the marginal sites (e.g., Jomsom, Dhunche, and Laohugou) were affected by fossil fuel combustion from the up-wind regions. The mass absorption cross-section of EC (MACEC) at 632 nm ranged from 6.56 to 14.7 m2 g−1, with an increasing trend from outside to inland of the TP. Urban areas had low MACEC values because such regions were mainly affected by local fresh emissions. In addition, large amount of brown carbon can decrease the MACEC values in cities of South Asia. Remote sites had high MACEC values because of the coating enhancement of aerosols.Influenced by emission, transport process, and weather condition, the CA concentrations and MACEC presented decreasing and increasing trends, respectively, from outside to inland of the TP.

Size-Segregated Characteristics of Carbonaceous Aerosols during the Monsoon and Non-Monsoon Seasons in Lhasa in the Tibetan Plateau

In this paper, we intensively collected atmospheric particulate matter (PM) with different diameters (size ranges: <0.49, 0.49–0.95, 0.95–1.5, 1.5–3.0, 3.0–7.2, and >7.2 μm) in Lhasa during the monsoon and non-monsoon seasons. The results clearly showed that the concentrations of PM, organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) during the non-monsoon season were much higher than the concentrations during the monsoon season. During the monsoon season, a bimodal size distribution of the OC and WSOC, which were at <0.49 μm and >7.2 μm, respectively, and a unimodal size distribution at <0.49 μm for the EC were observed. However, during the non-monsoon season, there was a trimodal size distribution of the OC and WSOC (<0.49 μm, 1.5–3.0 μm, and >7.2 μm), and a unimodal size distribution of the EC (<0.49 μm). Possible sources of the carbonaceous components were revealed by combining the particle size distribution and the correlation analysis. OC, EC, and WSOC were likely from the photochemical transformation of biogenic and anthropogenic VOC, and the incomplete combustion of biomass burning and fossil fuels at <0.49 μm, whilst they were also likely to be from various types of dust and biogenic aerosols at >7.2 μm. OC and WSOC at 1.5–3.0 μm were likely to have been from the burning of yak dung and photochemical formation. The above results may draw attention in the public and scientific communities to the issues of air quality in the Tibetan Plateau.

Assessment of Carbonaceous Aerosols at Mount Tai, North China: Secondary Formation and Regional Source Analysis

ABSTRACT To understand the concentrations, secondary organic aerosols (SOA) formation and source characteristics of carbonaceous aerosols in the regional environment of North China, a total of 48 fine particulate matter (PM2.5) samples were collected at the top of Mount Tai in the summer of 2015. Organic carbon (OC) and element carbon (EC) were analyzed and resolved into eight carbonaceous species using an Organic/Elemental Carbon Analyzer following the IMPROVE thermal-optical reflectance (TOR) protocol. OC and EC mass concentrations were 4.42 ± 3.04 and 1.58 ± 0.92 µg m–3, respectively, which were much higher than that of other domestic or abroad observation sites. Carbonaceous aerosols showed weekday-high trend during sampling period, which can be partly explained by anthropogenic effects. Higher concentrations of secondary organic carbon (SOC) were estimated by EC-tracer method during cloud/fog processing, indicating the fact that aqueous-phase reaction in droplets was an important pathway for SOC formation. Two source analysis approaches, consisting of Potential Source Contribution Function (PSCF) and Positive Matrix Factorization (PMF) were adopted to identify the regional sources and emission sources of carbonaceous species, and the apportion contributed by these sources. PSCF result demonstrated that the potential regional sources in the northwest, southwest and east coastal areas of Mount Tai contributed significantly to carbonaceous species loading in PM2.5. Additionally, three main emission sources were identified according to PMF result: diesel vehicle exhaust, biomass burning and mixed sources of gasoline vehicle exhaust and coal combustion, and each of sources had an average contribution of 26.4%, 19.0% and 54.5% to carbonaceous aerosols, respectively.

The characteristics of carbonaceous aerosol in Beijing during a season of transition

Carbonaceous aerosol was measured during fall of 2010 in Beijing. Daily variation of organic carbon (OC) was found to coincide with that of relative humidity (RH), and the OC to elemental carbon (EC) ratios were more than doubled during the more humid periods (RH above 0.75) compared to other conditions. This large increase in OC/EC could not be explained by the variations of primary biomass burning emissions but was accompanied by a five-fold increase in the sulfate to EC ratio. It was then inferred that secondary organic aerosol (SOA) formation was enhanced under the more humid conditions, presumably through aqueous-phase processes. This enhanced SOA formation might be partially associated with particles externally mixed with black carbon, as indicated by the RH-dependent relationships between aerosol optical attenuation and EC loading. In addition, organic aerosols exhibited different properties between the more humid and the other periods, such that they were less volatile and charred more significantly during thermal-optical analysis in the former case. These differences coincided with the evidence of enhanced SOA formation under the more humid conditions. This study highlights the necessity of incorporating aqueous-phase chemistry into air quality models for SOA.

Characteristics of Carbonaceous Aerosol in PM2.5 at Wanzhou in the Southwest of China

Hourly organic carbon (OC) and elemental carbon (EC) concentrations in PM2.5 were measured from June 2013 to May 2014 in Wanzhou, the second largest city in the Chongqing Municipality, in the southwest of China. Results show that the annual average concentrations of OC and EC were 13.16 ± 7.98 and 3.12 ± 1.51 μgC·m−3, respectively. Clear seasonal variations of OC and EC concentrations were observed, with their concentrations at minima in summer and maxima in winter. The diel concentration profile of OC and EC presented a bimodal pattern, which was attributed to the cooperative effects of local meteorological conditions and source emissions. The daily average OC/EC ratio ranged from 2.05 to 8.17 with an average of 4.15 for the whole study period. Strong correlations between OC and EC were found in winter and spring, indicating their common sources, while their correlations were poorer in summer and autumn, indicating that the influence of biogenic emissions and secondary organic carbon (SOC) were significant during those seasons. The estimated SOC concentrations were 2.19 ± 1.55, 7.66 ± 5.89, 5.79 ± 3.51, and 3.43 ± 2.26 μgC·m−3, accounting for 29.2%, 52.7%, 27.4%, and 30.5% of total organic carbon in summer, autumn, winter, and spring, respectively. The analysis of back trajectories suggested that high PM2.5, OC, and EC concentrations were associated with air masses originating from or passing over several industrial centers and urban areas in western and northwestern China. Air trajectories from the southeast with short pathways were the dominant trajectories arriving at Wanzhou, indicating that local sources had a big influence on PM2.5, OC, and EC concentrations.

Characteristics of Organic and Elemental Carbon in PM10 and PM2.5 in Yulin City, Guangxi

Two hundred eighteen PM10 and 202 PM2.5 samples were collected at three sampling sites to study the pollution characteristics of carbonaceous aerosols in Yulin from July 2015 to March 2016. Organic carbon (OC) and elemental carbon (EC) in the PM10 and PM2.5 samples were analyzed by a Multiwavelength Thermal/Optical Carbon Analyzer, and the characteristics, including pollution levels, temporal and spatial distributions, and possible sources of OC and EC, were investigated. The results showed that the OC and EC mass concentrations in PM10 in Yulin were 10.99 and 5.11 μg·m-3, respectively, while the OC and EC mass concentrations in PM2.5 were 7.51 and 4.70 μg·m-3, respectively. Strong correlations between OC and EC were found in PM10(R2=0.58) and PM2.5(R2=0.60). The winter average concentrations of secondary organic carbon (SOC) in PM10 and PM2.5 were 14.50 μg·m-3 and 6.74 μg·m-3, respectively. The SOC/OC ratios in both the PM10 and PM2.5 were higher than 0.5. The contribution of SOC to OC was 80.6% in PM10 and 77.7% in PM2.5, which were the highest in the summer, in accordance with the high temperature and strong solar radiation in the summer.

Insights into the characteristics and sources of primary and secondary organic carbon: High time resolution observation in urban Shanghai.

There is growing evidence suggesting that organic aerosols play an important role in the evolution of severe haze episodes. However, long-term investigations of the different characteristics of carbonaceous aerosols during haze and non-haze days are insufficient. In this work, hourly measurements of organic carbon (OC) and elemental carbon (EC) in PM2.5 were conducted in Shanghai, a megacity in Eastern China, over the course of a year from July 2013 to June 2014. Both OC and EC exhibited a bimodal diel pattern and were highly dependent on the wind speed and direction. The concentration-weighted trajectory (CWT) analysis illustrated that primary OC (POC) and EC were largely associated with regional and long-range transport. Secondary OC (SOC) formation was the strongest during the harvest season owing to significant biomass burning emissions from the adjacent Yangtze River Delta and farther agricultural regions. Compared to OC (6.7μgm-3) and EC (2.0μgm-3) in the non-haze days, higher levels of both OC (15.6μgm-3) and EC (7.7μgm-3) were observed in the haze days as expected, but with lower OC/EC ratios in the haze days (2.4) than in non-haze days (4.6). The proportion of POC and EC in PM2.5 remained relatively constant as a function of PM2.5 mass loadings, while that of SOC significantly decreased on the highly polluted days. It is concluded that the haze pollution in urban Shanghai was influenced more by the primary emissions (POC and EC), while the role of SOC in triggering haze was limited.

Characteristics of Carbonaceous Aerosol in a Typical Industrial City—Nanjing in Yangtze River Delta, China: Size Distributions, Seasonal Variations, and Sources

In order to investigate the size distributions and seasonal variations of carbonaceous aerosols (organic carbon (OC) and elemental carbon (EC)), the carbonaceous species were collected in Nanjing, a typical industrial city located in Yangtze River Delta, China, in the summer, autumn, and winter of 2013 and spring of 2014, and then analyzed by using a 9-stage Anderson-type aerosol sampler and DRI Model 2001A Thermal/Optical Carbon Analyzer. OC, EC, secondary organic carbon (SOC), and primary organic carbon (POC) exhibited obvious seasonal variations, with the highest levels in winter (39.1±14.0, 5.7 ± 2.1, 23.6 ± 11.7, and 14.1 ± 5.7 μg·m−3, respectively) and the lowest levels in summer (20.6 ± 6.7, 3.3 ± 2.0, 12.2 ± 3.8 and 8.4 ± 4.1 μg·m−3, respectively), and were mainly centralized in PM1.1 in four seasons. The concentrations of OC in PM1.1 varied in the order of winter > autumn > spring > summer, while EC ranked in the order of autumn > winter > summer > spring. In the PM1.1–2.1 and PM2.1–10, the concentrations of OC and EC decreased in the sequence of winter > spring > autumn > summer. The size spectra of OC, EC, and SOC had bimodal distributions in four seasons, except for EC with four peaks in summer. The size spectra of POC varied greatly with seasons, exhibiting bimodal distribution in winter, trimodal distribution in spring and summer, and four peaks in autumn. The OC/EC ratios were 7.0, 6.3, 7.6, and 6.9 in spring, summer, autumn and winter, respectively, which demonstrated the abundance of secondary organic aerosols in Nanjing. The sources of carbonaceous aerosol varied significantly with seasons, and were dominated by vehicle exhaust, and coal and biomass burning in PM2.1, and dominated by dust, and coal and biomass burning in PM2.1–10.

Light absorption characteristics of carbonaceous aerosols in two remote stations of the southern fringe of the Tibetan Plateau, China

Light absorption characteristics of carbonaceous aerosols are key considerations in climate forcing research. However, in situ measurement data are limited, especially on the Tibetan Plateau (TP) – the Third Pole of the world. In this study, the mass absorption cross section (MAC) of elemental carbon (EC) and water soluble organic carbon (WSOC) of total suspended particles at two high-altitude stations (Lulang station and Everest station) in the Tibetan Plateau (TP) were investigated. The mean MACEC values at 632 nm were 6.85 ± 1.39 m2 g−1 and 6.49 ± 2.81 m2 g−1 at these two stations, both of which showed little seasonal variations and were slightly higher than those of EC of uncoated particles, indicating that the enhancement of MACEC by factors such as coating with organic aerosols was not significant. The mean MACWSOC values at 365 nm were 0.84 ± 0.40 m2 g−1 and 1.18 ± 0.64 m2 g−1 at the two stations. Obvious seasonal variations of high and low MACWSOC values appeared in winter and summer, respectively, mainly reflecting photobleaching of light absorption components of WSOC caused by fluctuations in sunlight intensity. Therefore, this phenomenon might also exists in other remote areas of the world. The relative contributions of radiative forcing of WSOC to EC were 6.03 ± 3.62% and 11.41 ± 7.08% at these two stations, with a higher ratio in winter. As a result, both the contribution of WSOC to radiative forcing of carbonaceous aerosols and its seasonal variation need to be considered in radiative forcing related study.

Characteristics of carbonaceous aerosols in large-scale Asian wintertime outflows at Cape Hedo, Okinawa, Japan

We have performed long-term measurements of organic carbon (OC) and elemental carbon (EC) in atmospheric aerosols at Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS). Large-scale East Asian continental outflows of aerosols have frequently been observed at CHAAMS in both winter and spring, but large-scale air pollution (LSP) events in winter have not yet been described in the literature. Examination of PM2.5 in LSP events showed that it consisted mainly of carbonaceous aerosols and sulfate. We compared OC and EC concentrations measured at CHAAMS during LSP events with those measured at the same time in East Asian cities, and with concentrations measured at CHAAMS during an Asian dust event in spring 2006. The maximum OC and EC concentrations at Cape Hedo during LSP events were comparable to those at China Atmosphere Watch Network sites in China. The average OC concentration was also similar to concentrations measured at urban sites in Taipei (Taiwan), Seoul (Korea), and Tokyo (Japan); EC, however, was several times lower at Cape Hedo than EC concentrations at these urban sites. We identified three types of air masses associated with LSP events: Type 1, a polluted air mass composed of freshly emitted pollutants; Type 2, an air mass that underwent photochemical aging during transport from China to Okinawa; and Type 3, an air mass that was almost fully aged in China before being transported to Japan. Simulations of LSP events with a 3-D chemical transport model (Chemical Weather Forecasting System) indicated that Type 1 air masses were associated with “cone type” transport in a low-pressure system, and Type 2 air masses were associated with “giant puff type” transport by a migratory high-pressure system. Generally speaking, air pollutants are transported from China to CHAAMS in winter in association with the north or northwest monsoon. High levels of air pollutants in China in winter are due to higher emissions and poorer dispersion because of the low boundary layer height and low wind speeds. Our results suggest that LSP events occur when a cold front forms under accumulated air pollutants. The mass contribution of carbonaceous materials to PM2.5 during the LSP event in winter 2008 was 36%, much larger than the contribution of 19% during the spring 2006 dust event.

Fine carbonaceous aerosol characteristics at a megacity during the Chinese Spring Festival as given by OC/EC online measurements

The OC/EC online monitoring campaign was carried out in Tianjin of China from 8th February to 15th March 2015 during the Chinese Spring Festival period (CSFP). The concentrations of OC, EC, BC and other ambient pollutants (e.g. SO2, NO2 and PM2.5, etc.) in high time resolution were measured with related online-monitoring instruments. During the CSFP, according to the peaks of PM2.5 concentrations and number concentrations (NC) of aerosol particles with aerodynamic diameters between 0.3 and 2.5μm, five pollution-events were generally identified and displayed. These pollution-events were closely associated with large-scale fireworks displaying, combustion activities such as heating for winter, and the stable meteorological conditions, etc. During the CSFP, EC and OC concentrations showed variations up to one order of magnitude. The uncertainty of instrument itself and the difference for measured methods, further caused the differences between thermal OC (measured OC by thermal method) and optical OC (measured OC by optical method) concentrations, as well as between thermal EC (measured EC by thermal method) and optical EC (measured EC by optical method) concentrations. The high-concentration carbonaceous aerosols could enlarge the uncertainty of measuring instrument, reducing the correlations between OC and EC, and enhance the differences among thermal EC, optical BC and optical EC. The OC/EC ratios and the percentages of SOC/OC would be declined, when the pollution-events formed during the CSFP. Due to the different sources for thermal POC and thermal SOC, the correlation of the two was relatively lower (R2=0.39). Thermal POC dominated over thermal OC during the CSFP.

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−3ppm−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.

Size distribution characteristics of carbonaceous aerosol in Xishuangbanna, southwest China: a sign for biomass burning in Asia.

In 2012, size-segregated aerosol samples were collected in Xishuangbanna, a forest station in southwest China. The concentrations of organic and elemental carbon (OC and EC for short) were quantified with thermal/optical carbon analyzer in the filter samples. OC and EC exhibited similar seasonal patterns, with the highest concentrations in spring, possibly due to the influence of biomass burning in south and southeast Asia. The mass size distributions of OC and EC were bimodal in all the sampling seasons, each with a dominant peak in the fine mode of 0.4-0.7 μm and a coarse peak in the size range of 2.1-4.7 μm. In fine mode, OC and EC showed smaller geometric mean diameters (GMDs) during winter. OC and EC were prone to be more concentrated in fine particles in spring and winter than in summer and autumn. Furthermore, EC was more abundant in fine particles than OC. Good correlations (R(2) = 0.75-0.82) between OC and EC indicated that they had common dominant sources of combustion such as biomass burning and fossil fuel combustion emissions. The daily average OC/EC ratios ranged from 2.1 to 9.1, more elevated OC/EC ratios being found in the winter.

Emission Regulations Altered the Concentrations, Origin, and Formation of Carbonaceous Aerosols in the Tokyo Metropolitan Area

To investigate the effects of the regulations of diesel and non-methane hydrocarbon (NMHCs) emissions in the Tokyo metropolitan area (TMA) on the characteristics of carbonaceous aerosols (organic carbon (OC) and elemental carbon (EC)), we conducted field observations to characterize carbonaceous aerosols in the TMA in the summer of 2004 and 2014 (the end of July-middle of August). Following the enforcement of diesel emission regulations, EC concentrations showed a four-fold decrease from 2004 to 2014. However, OC concentrations showed no significant decrease in the last decade. Multiple chemical analyses revealed the differences in the impacts of the contribution of oxygenated fraction, biogenic NMHCs on OC, and the secondary organic aerosol-Ozone relationship between 2004 and 2014. Further investigations into the emission inventory for recent years, especially in terms of precursor gases, are needed for better prediction of OC in the TMA using chemical transport models.

Size-Segregated Characteristics of Carbonaceous Aerosols over the Northwestern Indo-Gangetic Plain: Year Round Temporal Behavior

ABSTRACTSize-segregated aerosol samples (PM 7.2) were collected over Patiala (30.33°N, 76.40°E; 250 m amsl), a semi-urban city located in northwestern Indo-Gangetic Plain (IGP) during October, 2012 to September, 2013. These samples were analyzed for carbonaceous aerosols (organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC)) to study their temporal variation, prevailing emission source (s) and secondary formation processes. Annual average of total suspended particulates (TSP) concentration, estimated by adding the aerosol concentrations in different size ranges, was found to be 199 ± 82 µg m–3, varying from 88–387 µg m–3 with majority of particulate mass found in submicron size (PM 75%) and WSOC (> 80%) was observed in submicron size, suggesting that OC mainly comes from combustion and/or secondary source (s). It has been observed that almost half of OC is secondary. On the other hand, climate forcing agent EC in PM<0.95 varied from 1.1 to 9.8 µg m–3 (4.8 ± 2.2 µg m–3). High mass ratios of OC/EC (~1.5–7.2) and WSOC/OC (~0.33–0.68) indicate the relative dominance of biomass burning emission over the study region. Total carbonaceous aerosols account for ~10–59% of submicron particulates mass (PM<0.95), indicating that fine particulates are enriched with carbonaceous species. These results have implications to regional climate model development and validation.

Concentrations and light absorption characteristics of carbonaceous aerosol in PM 2.5 and PM 10 of Lhasa city, the Tibetan Plateau

Abstract Light absorption properties of carbonaceous aerosol strongly influence the Earth's radiative balance, yet the related knowledge is limited for the Tibetan Plateau (TP), the highest and largest plateau in the world. In this study, organic carbon (OC), elemental carbon (EC) and water soluble organic carbon (WSOC) of PM 2.5 and PM 10 of Lhasa collected from May 2013 to March 2014 were studied. It showed that daily-average concentrations of OC, EC and WSOC of PM 2.5 and PM 10 were lower than those of other megacities. Lhasa PM 2.5 was characterized by low OC/EC ratio (1.46 ± 0.55), which was similar to that of Lhasa roadside PM 2.5 (1.25 ± 0.45), reflecting mainly direct influence of primary emissions and less secondary formation. Hence, although Lhasa atmosphere is relatively clean, it is intensively influenced by local vehicle emissions. Mass absorption cross-section of EC (MAC EC ) for both PM 2.5 and PM 10 at 632 nm were 7.19 ± 1.19 m 2 g −1 and 7.98 ± 2.32 m 2 g −1 , respectively, both of which had similar variation patterns to OC/EC and secondary OC (SOC)/OC, indicating that the increase of MAC EC might be caused by coating with organic aerosol. Additionally, the loading of EC for both PM 2.5 and PM 10 showed logarithmic relationships with those of optical attenuation (ATN) of EC, implying that the shadowing effect enhanced logarithmic with increased EC concentration. MAC of WSOC at 365 nm for PM 2.5 (0.74 ± 0.22 m 2 g −1 ) and PM 10 (0.78 ± 0.21 m 2 g −1 ) were also close to reported values of other cities mainly influenced by fossil combustion. Additionally, attenuation at 365 nm of WSOC of both PM 2.5 and PM 10 showed the same relationship with their WSOC concentrations, implying no difference for light absorption properties of WSOC for these two grain sizes.

Optical and thermal characteristics of carbonaceous aerosols measured at an urban site in Gwangju, Korea, in the winter of 2011

ABSTRACTCarbonaceous components (organic carbon [OC] and elemental carbon [EC]) and optical properties (light absorption and scattering) of fine particulate matter (aerodynamic diameter <2.5 μm; PM2.5) were simultaneously measured at an urban site in Gwangju, Korea, during the winter of 2011. OC was further classified into OC1, OC2, OC3, and OC4, based on a temperature protocol using a Sunset OC/EC analyzer. The average OC and EC concentrations were 5.0 ± 2.5 and 1.7 ± 0.9 μg C m−3, respectively. The average single-scattering albedo (SSA) at a wavelength of 550 nm was 0.58 ± 0.11, suggesting that the aerosols observed in the winter of 2011 had a local warming effect in this area. During the whole sampling period, “stagnant PM” and “long-range transport PM” events were identified. The light absorption coefficient (babs) was higher during the stagnant PM event than during the long-range transport PM event due to the existence of abundant light-absorbing OC during the stagnant PM event. In particular, the OC2 and OC3 concentrations were higher during the stagnant PM event than those during the long-range transport event, suggesting that OC2 and OC3 might be more related to the light-absorbing OC. The light scattering coefficient (bscat) was similar between the events. On average, the mass absorption efficiency attributed to EC (σEC) was 9.6 m2 g−1, whereas the efficiency attributed to OC (σOC) was 1.8 m2 g−1 at λ = 550 nm. Furthermore, the σEC is comparable among the PM event days, but the σOC for the stagnant PM event was significantly higher than that for the long-range transport PM event (1.7 vs. 0.5).Implications: Optical and thermal properties of carbonaceous aerosol were measured at Gwangju, and carbonaceous aerosol concentration and optical property varied between “stagnant PM” and “long-range transport PM” events. More abundant light absorbing OC was observed during the stagnant PM event.

Characteristics of carbonaceous aerosols in Emilia-Romagna (Northern Italy) based on two fall/winter field campaigns

The carbonaceous aerosol in Emilia-Romagna region (Northern Italy) was characterized in two fall/winter monitoring campaigns conducted through the years 2011–2012 and 2012–2013. Nearly 650 PM2.5 samples were collected at three monitoring stations describing urban background (main city Bologna, MS, Parma and Rimini) and one rural background site (San Pietro, SP). OC and EC values were measured by the thermal–optical transmittance method (TOT). Low flow-rate sampling strategy (24m3 air volume per day) was used to reduce loading of light absorbing material on the filter surface in order to ensure the correct OC/EC discrimination.The TC values measured in winter 2011–2012 ranged from 9.8μgCm−3 at San Pietro to 12.0μgCm−3 at Parma, consisting of OC from 8.6μgCm−3 at SP to 9.9μgCm−3 at MS and EC from 1.3μgCm−3 at SP to 2.5μgCm−3 at Rimini. In winter 2012–2013, lower values were in general found with TC values ranging from 7.8 to 9.1μgCm−3 consisting of OC from 5.1 to 7.0μgCm−3 and EC from 1.5 to 2.2μgCm−3.Such differences can be likely explained by higher pollutant emissions related to domestic heating in colder fall/winter 2011/2012 (mean temperature≈2°C in comparison with ≈ 7°C in winter 2012/2013). This hypothesis is supported by high levels of levoglucosan, as unambiguous tracer for biomass burning emission, and of polycyclic aromatic hydrocarbons related to combustion (levoglucosan≃1000ngm−3 and burning PAHs≃4ngm−3 at MS and SP sites).