Raman spectroscopic characterization of carbonaceous aerosols

We have used Raman spectroscopy to characterize a variety of carbon-containing particulate matter, including samples collected in ambient urban atmospheres. Based on the Raman spectra of known, commercial particles, we derive a simple empirical model that reflects their microchemistry and microphysics. This model gives information on the crystal size and morphology of the graphitic component, which correlates with the known characteristics of the commercial samples. We derive similar information about the graphitic component of the ambient particles, and suggest that this method might be used to characterize ambient particles systematically in the future.     

Sulfate and carbonaceous aerosols in Beijing China

Results of our aerosol study, performed during 1983–1984 in Beijing, demonstrate that ambient carbonaceous aerosols are derived principally from coal combustion. Different SO₂ oxidation processes have been observed in summer and winter. The winter sulfate appears to be produced locally and associated with products of incomplete combustion.     

Characteristics of carbonaceous aerosols in Beijing, China

Carbonaceous aerosols and PM10 were monitored from September 8 to November 30, 2002, in a semi-urban site (Tsinghua University) in Beijing. Daily concentrations of OC and EC ranged from 7.1 to 65.9 microgCm(-3) and from 1.3 to 26.1 microgCm(-3), with the overall average concentrations of 21.2 microgCm(-3) and 7.3 microgCm(-3), respectively. The diurnal variation of carbonaceous concentrations on 2 h basis presented two-peak trend, which was attributed to the cooperative effect of local meteorological conditions and anthropogenic sources such as traffic exhaust and human outdoor activities. Daily average OC/EC ratio varied between 1.5 and 5.3 with an average of 3.0. Strong correlation between OC and EC (R2=0.8) indicated that their main sources were common. The frequency of OC/EC ratio presented Gaussian normal distribution trend in fall, of which the peak value appeared in the range of 2.8-5. In winter, it presented bi-peak mode, with the first peak near 1.4-1.6, and the second between 2.8 and 5. The high value (2.8-5) implied the SOC formation in both seasons, and the low one probably suggested the primary OC/EC ratio from coal burning in winter. Averagely, PM10 and carbonaceous species exhibited higher concentrations in Wednesday than in other weekdays, which could be ascribed to the low wind speed (1.6 ms(-1)) and high humidity (62.9%). OC was the abundant component accounting for 76% of TC. OC and EC contributed 15% and 5% to PM10, respectively. The estimation on a minimum OC/EC ratio (1.5) basis showed that SOC accounted more than 50% for the total organic carbon. Even in winter, the SOC contribution to OC was also significant, as high as 40%.     

Source contributions to carbonaceous aerosols in the Tennessee Valley Region

Sources of carbonaceous aerosols collected from three sites of Chattanooga, TN (CH), Muscle Shoals, AL (MS), and Look Rock, TN (LR) in the Tennessee Valley Region (TVR) were apportioned using both organic tracer-based chemical mass balance (CMB) modeling and radiocarbon (¹⁴C) measurement and the results were compared. Eight sources were resolved by CMB, among which wood combustion (averaging 0.92 μg m⁻³) was the largest contributor to primary organic carbon (OC) concentrations, followed by gasoline exhaust (0.35 μg m⁻³), and diesel exhaust (0.18 μg m⁻³). The identified primary sources accounted for 43%, 71%, and 14% of measured OC at CH, MS, and LR, respectively. Contributions from the eight primary sources resolved by CMB could explain 107±10% of ambient elemental carbon (EC) concentrations, with diesel exhaust (66±32%) and wood combustion (37±33%) as the most important contributors. The fossil fractions in total carbon determined by ¹⁴C measurements were in reasonably good agreement with that in primary (OC+EC) carbon apportioned by CMB in the MS winter samples. The comparison between the ¹⁴C and CMB results revealed that contemporary sources dominated other OC in the TVR, especially in summertime (84% contemporary).     

On the variability of Black Smoke and carbonaceous aerosols in the Netherlands

The study addresses the characteristics of elemental carbon (EC) and organic carbon (OC) distributions in the Netherlands by using Black Smoke (BS) data in combination with dedicated measurements and modelling. The BS levels indicate a large-scale background concentration over the Netherlands with low spatial variability and a gradient with highest levels (∼9 μg m⁻³) in the south gradually decreasing to the north-west (∼5.5 μg m⁻³). The BS concentrations at rural sites in the Netherlands are highly correlated due to common (diffuse) sources and large-scale meteorology. Superimposed on the regional background are the contributions of local/urban sources. Urban and rural BS levels show a distinct variation over the week with minimum levels on Sundays.BS levels do not reflect a real concentration as they are obtained via an optical measurement in combination with an outdated calibration curve to arrive at total suspended particles (TSP). We have found that the relation between BS and EC in the Netherlands is linear and highly correlated but dependent on station type. Application of these relations to the BS time series yields a gradient in the rural background EC concentration from 0.5 μg m⁻³ in the north to 0.7 μg m⁻³ in the south of the Netherlands. The relationship between OC and BS appears to be location specific and is determined by the BS–EC relation in combination with a characteristic OC/EC ratio. OC/EC ratios are ∼5 at regional background sites and ∼2 at traffic locations. Minimum OC/EC ratios at the traffic sites reflect the primary OC/EC ratio of traffic. We argue that estimation of secondary organic aerosol by assuming the minimum OC/EC ratio to be a proxy for the primary OC/EC is not allowed since this approach does not account for sources with high OC/EC ratios. Based on European scale modelling and the measured data, we estimate that national sources contribute ∼40–60% to Dutch EC levels.The rather costly and laborious EC measurements provide a better indicator of the carbonaceous fraction in ambient particulate matter (PM) but the cheap BS method may provide valuable information on spatial distribution of EC when used in combination with validation sites to characterise the EC–BS relationship.     

Time-resolved measurements of PM2.5 carbonaceous aerosols at Gosan, Korea

In order to better understand the characteristics of atmospheric carbonaceous aerosol at a background site in Northeast Asia, semicontinuous organic carbon (OC) and elemental carbon (EC), and time-resolved water-soluble organic carbon (WSOC) were measured by a Sunset OC/ EC and a PILS-TOC (particle-into-liquid sampler coupled with an online total organic carbon) analyzer, respectively, at the Gosan supersite on Jeju Island, Korea, in the summer (May 28-June 17) and fall (August 24-September 30) of 2009. Hourly average OC concentration varied in the range of approximately 0.87-28.38 microgC m-3, with a mean of 4.07+/- 2.60 microgC m-3, while the hourly average EC concentration ranged approximately from 0.04 to 8.19 .microgC m-3, with a mean of 1.35 +/- 0.71 microgC m-3, from May 28 to June 17, 2009. During the fall season, OC varied in the approximate range 0.9-9.6 microgC m-3, with a mean of 2.30 +/-0.80 microgC m-3, whereas EC ranged approximately from 0.01 to 5.40 microgC m-3, with a mean of 0.66 +/- 0.38 microgC m-3. Average contributions of EC to TC and WSOC to OC were 26.0% +/- 9.7% and 20.6% +/-7.4%, and 37.6% +/- 23.5% and 57.2% +/- 22.2% during summer and fall seasons, respectively. As expected, clear diurnal variation of WSOC/OC was found in summer, varying from 0.22 during the nighttime up to 0.72 during the daytime, mainly due to the photo-oxidation process. In order to investigate the effect of air mass pathway on the characteristics of carbonaceous aerosol, 5-day back-trajectory analysis was conducted using the HYSPLIT model. The air mass pathways were classified into four types: Continental (CC), Marine (M), East Sea (ES) and Korean Peninsula (KP). The highest OC/EC ratio of 3.63 was observed when air mass originated from the Continental area (CC). The lowest OC/EC ratio of 0.79 was measured when air mass originated from the Marine area (M). A high OC concentration was occasionally observed at Gosan due to local biomass burning activities. The contribution of secondary OC to total OC varied approximately between 8.4% and 32.2% and depended on air mass type.     

Atmospheric carbonaceous aerosols over grasslands of central Europe and a Boreal forest

A labour-intensive analytical technique was applied to atmospheric particulate matter samples collected in a German urban/industrial influenced grassland location (Melpitz) and in a Finnish forest area (Hyyti?l?) in order to achieve a detailed chemical speciation of the organic content. The representative nature of the solvent and water-extractable fractions was determined. The organic compounds identified in the solvent extracts are represented by primary compounds with both anthropogenic and biogenic origin, which mainly derive from the vegetation waxes and from petrogenic sources. Secondary products resulting from the oxidation of volatile organic compounds were also detected. The German meadow presented the highest levels of sugars and acidic compounds in the water extracts, whilst polyols were the most abundant class in the Finnish forest. The major compounds of these classes were malic acid, mannitol, arabitol, glucose and sucrose. Levoglucosan was also found in the water extract.     

Urban impacts on regional carbonaceous aerosols: Case study in central Texas

Rural and background sites provide valuable information on the concentration and optical properties of organic, elemental, and water-soluble organic carbon (OC, EC, and WSOC), which are relevant for understanding the climate forcing potential of regional atmospheric aerosols. To quantify climate- and air quality-relevant characteristics of carbonaceous aerosol in the central United States, a regional background site in central Texas was chosen for long-term measurement. Back trajectory (BT) analysis, ambient OC, EC, and WSOC concentrations and absorption parameters are reported for the first 15 months of a long-term campaign (May 2011–August 2012). BT analysis indicates consistent north–south airflow connecting central Texas to the Central Plains. Central Texas aerosols exhibited seasonal trends with increased fine particulate matter (<2.5 μm aerodynamic diameter, PM_2.5) and OC during the summer (PM_2.5 = 10.9 μg m^?3 and OC = 3.0 μg m^?3) and elevated EC during the winter (0.22 μg m^?3). When compared to measurements in Dallas and Houston, TX, central Texas OC appears to have mixed urban and rural sources. However, central Texas EC appears to be dominated by transport of urban emissions. WSOC averaged 63% of the annual OC, with little seasonal variability in this ratio. To monitor brown carbon (BrC), absorption was measured for the aqueous WSOC extracts. Light absorption coefficients for EC and BrC were highest during summer (EC MAC = 11 m² g^?1 and BRC MAE₃₆₅ = 0.15 m² g^?1). Results from optical analysis indicate that regional aerosol absorption is mostly due to EC with summertime peaks in BrC attenuation. This study represents the first reported values of WSOC absorption, MAE₃₆₅, for the central United States.

Implications:Background concentration and absorption measurements are essential in determining regional potential radiative forcing due to atmospheric aerosols. Back trajectory, chemical, and optical analysis of PM_2.5 was used to determine climatic and air quality implications of urban outflow to a regional receptor site, representative of the central United States. Results indicate that central Texas organic carbon has mixed urban and rural sources, while elemental carbon is controlled by the transport of urban emissions. Analysis of aerosol absorption showed black carbon as the dominant absorber, with less brown carbon absorption than regional studies in California and the southeastern United States.     

Spatial variability of carbonaceous aerosols and associated source tracers in two cites in the Midwestern United States

Semi-continuous and 24-h averaged measurements of fine carbonaceous aerosols were made concurrently at three sites within each of two U.S. Midwestern Cities; Detroit, Michigan and Cleveland, Ohio; during two, one-month intensive campaigns conducted in July of 2007 and January & February of 2008. A comparison of 24-h measurements revealed substantial intra-urban variability in carbonaceous aerosols consistent with the influence of local sources, and excesses in both PM_2.5 organic carbon (OC) and elemental carbon (EC) were identified at individual sites within each city. High time-resolved black carbon (BC) measurements indicated that elemental carbon concentrations were higher at sites adjacent to freeways and busy surface streets, and temporal patterns suggested that excess EC at sites adjacent to freeways was dominated by mobile source emissions while excesses in EC away from traffic corridors was dominated by point/area source emissions. The site-to-site variability in OC concentrations was approximately 7% within the neighborhood scale (0.5–4 km) and between 4 and 27% at the urban scale (4–100 km). In contrast, measurements of organic source tracers, in conjunction with a Chemical Mass Balance (CMB) source-apportionment model, indicated that the spatial variation in the contribution of both mobile and stationary sources to PM_2.5 OC often exceeded the variation in OC mass concentration by a factor of 3 or more. Markers for mobile sources, biomass smoke, natural gas, and coal combustion differed by as much as 60% within the neighborhood scale and by greater than 200% within the urban scale. The observations made during this study suggest that the urban excess of carbonaceous aerosols is much more complex than has been previously reported and that a more rigorous, source-oriented approach should be taken in order to assess the risk associated with exposure to carbonaceous aerosols within the industrialized environments of the Midwestern United States.     

Characterization of carbonaceous aerosols over Delhi in Ganga basin: seasonal variability and possible sources

The mass concentration of carbonaceous species, organic carbon (OC), and elemental carbon (EC) using a semicontinuous thermo-optical EC-OC analyzer, and black carbon (BC) using an Aethalometer were measured simultaneously at an urban mega city Delhi in Ganga basin from January 2011 to May 2012. The concentrations of OC, EC, and BC exhibit seasonal variability, and their concentrations were ～2 times higher during winter (OC 38.1?±?17.9 μg m^?3, EC 15.8?±?7.3 μg m^?3, and BC 10.1?±?5.3 μg m^?3) compared to those in summer (OC 14.1?±?4.3 μg m^?3, EC 7.5?±?1.5 μg m^?3, and BC 4.9?±?1.5 μg m^?3). A significant correlation between OC and EC (R?=?0.95, n?=?232) indicate their common emission sources with relatively lower OC/EC ratio (range 1.0–3.6, mean 2.2?±?0.5) suggests fossil fuel emission as a major source of carbonaceous aerosols over the station. On average, mass concentration of EC was found to be ～38 % higher than BC during the study period. The measured absorption coefficient (b_abs) was significantly correlated with EC, suggesting EC as a major absorbing species in ambient aerosols at Delhi. Furthermore, the estimated mass absorption efficiency (σ_abs) values are similar during winter (5.0?±?1.5 m² g^?1) and summer (4.8?±?2.8 m² g^?1). Significantly high aerosol loading of carbonaceous species emphasize an urgent need to focus on air quality management and proper impact assessment on health perspective in these regions.     

Impact of anthropogenic emissions and open biomass burning on regional carbonaceous aerosols in South China

Carbonaceous aerosols were studied at three background sites in south and southwest China. Hok Tsui in Hong Kong had the highest concentrations of carbonaceous aerosols (OC = 8.7 ± 4.5 μg/m³, EC = 2.5 ± 1.9 μg/m³) among the three sites, and Jianfeng Mountains in Hainan Island (OC = 5.8 ± 2.6 μg/m³, EC = 0.8 ± 0.4 μg/m³) and Tengchong mountain over the east edge of the Tibetan Plateau (OC = 4.8 ± 4.0 μg/m³, EC = 0.5 ± 0.4 μg/m³) showed similar concentration levels. Distinct seasonal patterns with higher concentrations during the winter, and lower concentrations during the summertime were observed, which may be caused by the changes of the regional emissions, and monsoon effects. The industrial and vehicular emissions in East, Southeast and South China, and the regional open biomass burning in the Indo-Myanmar region of Asia were probably the two major potential sources for carbonaceous matters in this region.     

Comparative analysis of organic and elemental carbon concentrations in carbonaceous aerosols in three European cities

Sampling and analysis of carbonaceous compounds in particulate matter presents a number of difficulties related to artefacts during sampling and to the distinction between organic (OC) and elemental carbon (EC) during analysis. Our study reports on a comparative analysis of OC, EC and WSOC (water-soluble organic carbon) concentrations, as well as sampling artefacts, for PM2.5 aerosol in three European cities (Amsterdam, Barcelona and Ghent) representing Southern and Western European urban environments. Comparability of results was ensured by using a single system for sample analysis from the different sites. OC and EC concentrations were higher in the vicinity of roads, thus having higher levels in Amsterdam (3.9–6.7 and 1.7–1.9 μg m⁻³, respectively) and Barcelona (3.6–6.9 and 1.5–2.6 μg m⁻³) than in Ghent (2.7–5.4 and 0.8–1.2 μg m⁻³). A relatively larger influence of secondary organic aerosols (SOA), as deduced from a larger OC/EC ratio, was observed in Ghent. In absolute sense, WSOC concentrations were similar at the three sites (1.0–2.3 μg m⁻³). Positive artefacts were higher in Southern (11–16% of the OC concentration in Barcelona) than in Western Europe (5–12% in Amsterdam, 5–7% in Ghent). During special episodes, the contribution of carbonaceous aerosols from non-local sources accounted for 67–69% of the OC concentration in Western Europe, and for 44% in Southern Europe.     

Determination of primary and secondary sources of organic acids and carbonaceous aerosols using stable carbon isotopes

Stable carbon isotope ratio (δ¹³C) data can provide important information regarding the sources and the processing of atmospheric organic carbon species. Formic, acetic and oxalic acid were collected from Zurich city in August–September 2002 and March 2003 in the gas and aerosol phase, and the corresponding δ¹³C analysis was performed using a wet oxidation method followed by isotope ratio mass spectrometry. In August, the δ¹³C values of gas phase formic acid showed a significant correlation with ozone (coefficient of determination (r²) = 0.63) due to the kinetic isotope effect (KIE). This indicates the presence of secondary sources (i.e. production of organic acids in the atmosphere) in addition to direct emission. In March, both gaseous formic and acetic acid exhibited similar δ¹³C values and did not show any correlation with ozone, indicating a predominantly primary origin. Even though oxalic acid is mainly produced by secondary processes, the δ¹³C value of particulate oxalic acid was not depleted and did not show any correlation with ozone, which may be due to the enrichment of ¹³C during the gas - aerosol partitioning.The concentrations and δ¹³C values of the different aerosol fractions (water soluble organic carbon, water insoluble organic carbon, carbonate and black carbon) collected during the same period were also determined. Water soluble organic carbon (WSOC) contributed about 60% to the total carbon and was enriched in ¹³C compared to other fractions indicating a possible effect of gas - aerosol partitioning on δ¹³C of carbonaceous aerosols. The carbonate fraction in general was very low (3% of the total carbon).     

Evaluations of the chemical mass balance method for determining contributions of gasoline and diesel exhaust to ambient carbonaceous aerosols

The US. Department of Energy Gasoline/Diesel PM Split Study was conducted to assess the sources of uncertainties in using an organic compound-based chemical mass balance receptor model to quantify the relative contributions of emissions from gasoline (or spark ignition [SI]) and diesel (or compression ignition [CI]) engines to ambient concentrations of fine particulate matter (PM2.5) in California's South Coast Air Basin (SOCAB). In this study, several groups worked cooperatively on source and ambient sample collection and quality assurance aspects of the study but worked independently to perform chemical analysis and source apportionment. Ambient sampling included daily 24-hr PM2.5 samples at two air quality-monitoring stations, several regional urban locations, and along freeway routes and surface streets with varying proportions of automobile and truck traffic. Diesel exhaust was the dominant source of total carbon (TC) and elemental carbon (EC) at the Azusa and downtown Los Angeles, CA, monitoring sites, but samples from the central part of the air basin showed nearly equal apportionments of CI and SI. CI apportionments to TC were mainly dependent on EC, which was sensitive to the analytical method used. Weekday contributions of CI exhaust were higher for Interagency Monitoring of Protected Visual Environments (IMPROVE; 41+/-3.7%) than Speciation Trends Network (32+/-2.4%). EC had little effect on SI apportionment. SI apportionments were most sensitive to higher molecular weight polycyclic aromatic hydrocarbons (indeno[123-cd]pyrene, benzo(ghi)perylene, and coronene) and several steranes and hopanes, which were associated mainly with high emitters. Apportionments were also sensitive to choice of source profiles. CI contributions varied from 30% to 60% of TC when using individual source profiles rather than the composites used in the final apportionments. The apportionment of SI vehicles varied from 1% to 12% of TC depending on the specific profile that was used. Up to 70% of organic carbon (OC) in the ambient samples collected at the two fixed monitoring sites could not be apportioned to directly emitted PM emissions.     

Characterisation of PM10 atmospheric aerosols for the wet season 2005 at two sites in East Africa

Ambient daily PM₁₀ aerosol samples were collected at two sites in Tanzania in May and June 2005 (during the wet season), and their chemical characteristics were studied. The sites were a rural site in Morogoro and an urban kerbside site in Dar es Salaam. A Gent PM₁₀ stacked filter unit sampler with sequential Nuclepore polycarbonate filters, providing fine and coarse size fractions, and a PM₁₀ sampler with quartz fibre filters were deployed. Parallel collections of 24 h were made with the two samplers and the number of these collections was 13 in Morogoro and 16 in Dar es Salaam. The average mass concentration of PM₁₀ was 27 ± 11 μg/m³ in Morogoro and 51 ± 21 μg/m³ in Dar es Salaam. In Morogoro, the mean concentrations of organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were 6.8, 0.51, and 2.8 μg/m³, respectively. In contrast, higher mean concentrations (11.9, 4.6, and 3.3 μg/m³, respectively) were obtained for Dar es Salaam. At both sites, species and elements, such as black carbon, NH₄⁺, non-sea-salt SO₄^2?, K, and Ni (and at Dar es Salaam also V, As, Br, and Pb) were mainly present in the fine size fraction. The common crustal and sea-salt elements, including Na, Mg, Al, Si, Cl, Ca, Ti, Mn, Fe, and Sr, and also NO₃^? and P (and to a lesser extent Cu and Zn) were concentrated in the coarse particles. Aerosol chemical mass closure indicated that the PM₁₀ mass in Morogoro consisted, on average, of 48% organic matter (OM), 44% crustal matter, 4% sea salt, and 2% EC, while in Dar es Salaam OM, crustal matter, sea salt, and EC represented 37%, 32%, 9%, and 9% of the PM₁₀ mass. The contributions of the secondary inorganic aerosol (non-sea-salt sulphate, nitrate, and ammonium) were small, i.e., only 5% in total at each site. Carbonaceous materials and crustal matter were thus the most important components of the PM₁₀ mass. It is suggested that biomass burning is a major contributor to the OM; at Dar es Salaam there is also a very substantial contribution from traffic. A source apportionment calculation indicated that 68% of the OC at this site originated from traffic exhaust versus 32% from charcoal burning. The crustal matter at Morogoro is likely mainly attributable to soil dust resuspension, whereas in Dar es Salaam it is likely mostly resuspended road dust.     

Concentrations,seasonal variations,and transport of carbonaceous aerosols at a remote Mountainous region in western China

Carbonaceous aerosol concentrations were determined for total suspended particle samples collected from Muztagh Ata Mountain in western China from December 2003 to February 2006. Elemental carbon (EC) varied from 0.004 to 0.174 μg m^?3 (average = 0.055 μg m^?3) while organic carbon (OC) ranged from 0.12 to 2.17 μg m^?3 and carbonate carbon (CC) from below detection to 3.57 μg m^?3. Overall, EC was the least abundant fraction of carbonaceous species, and the EC concentrations approached those in some remote polar areas, possibly representing a regional background. Low EC and OC concentrations occurred in winter and spring while high CC in spring and summer was presumably due to dust from the Taklimakan desert, China. OC/EC ratios averaged 10.0, and strong correlations between OC and EC in spring–winter suggest their cycles are coupled, but lower correlations in summer–autumn suggest influences from biogenic OC emissions and secondary OC formation. Trajectory analyses indicate that air transported from outside of China brings ～0.05 μg m^?3 EC, ～0.42 μg m^?3 OC, and ～0.10 μg m^?3 CC to the site, with higher levels coming from inside China. The observed EC was within the range of loadings estimated from a glacial ice core, and implications of EC-induced warming for regional climate and glacial ice dynamics are discussed.     

Chemical composition of Swiss aerosols from the Jungfraujoch

Atmospheric aerosols have been sampled monthly during 19 months at the Jungfraujoch in Switzerland (3752 m above sea level). The geometric mean concentration of total suspended particulates is 3.1 μgm⁻³. Also the concentrations of 31 trace elements were determined in the samples. The concentration variations show a seasonal pattern for all elements, but most pronounced for the lithophilic elements. The geometric mean concentrations are compared to those measured at the other remote locations and at polluted sites. Rock and aerosol enrichment factors are calculated. The chemical compositions of the Jungfrau aerosol is very similar to that collected elsewhere. Also at remote locations the relatively volatile chalcophilic elements are enriched.     

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

Carbonaceous components (organic carbon [OC] and elemental carbon [EC]) and optical properties (light absorption and scattering) of fine particulate matter (aerodynamic diameter <2.5 μm; PM_2.5) 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 (b_abs) 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 (b_scat) was similar between the events. On average, the mass absorption efficiency attributed to EC (σ_EC) was 9.6 m² g^?1, whereas the efficiency attributed to OC (σ_OC) was 1.8 m² g^?1 at λ = 550 nm. Furthermore, the σ_EC is comparable among the PM event days, but the σ_OC 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 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

Environmental Science and Pollution Research - Simultaneous observations (2014–2017) of organic carbon (OC) and elemental carbon (EC) are made over a high-altitude site (Nainital,...