Organic and elemental carbon associated to PM10 and PM2.5 at urban sites of northern Greece

Organic carbon (OC) and elemental carbon (EC) concentrations, associated to PM₁₀ and PM_2.5 particle fractions, were concurrently determined during the warm and the cold months of the year (July–September 2011 and February–April 2012, respectively) at two urban sites in the city of Thessaloniki, northern Greece, an urban-traffic site (UT) and an urban-background site (UB). Concentrations at the UT site (11.3?±?5.0 and 8.44?±?4.08 14 μg m^?3 for OC₁₀ and OC_2.5 vs. 6.56?±?2.14 and 5.29?±?1.54 μg m^?3 for EC₁₀ and EC_2.5) were among the highest values reported for urban sites in European cities. Significantly lower concentrations were found at the UB site for both carbonaceous species, particularly for EC (6.62?±?4.59 and 5.72?±?4.36 μg m^?3 for OC₁₀ and OC_2.5 vs. 0.93?±?0.61 and 0.69?±?0.39 μg m^?3 for EC₁₀ and EC_2.5). Despite that, a negative UT-UB increment was frequently evidenced for OC_2.5 and PM_2.5 in the cold months possibly indicative of emissions from residential wood burning at the urban-background site. At both sites, cconcentrations of OC fractions were significantly higher in the cold months; on the contrary, EC fractions at the UT site were prominent in the warm season suggesting some influence from maritime emissions in the nearby harbor area. Secondary organic carbon, being estimated using the EC tracer method and seasonally minimum OC/EC ratios, was found to be an appreciable component of particle mass particularly in the cold season. The calculated secondary contributions to OC ranged between 35 and 59 % in the PM₁₀ fraction, with relatively higher values in the PM_2.5 fraction (39–61 %). The source origin of carbonaceous species was investigated by means of air parcel back trajectories, satellite fire maps, and concentration roses. A local origin was mainly concluded for OC and EC with limited possibility for long range transport of biomass (agricultural waste) burning aerosol.     

Characteristics of PM2.5 carbonaceous aerosol in the Sihwa industrial area,Korea

In order to investigate the characteristics of carbonaceous fine aerosols, PM_2.5 particulate samples were collected in the Sihwa industrial complex area between February 1998 and 1999 and in Seoul between 31 May and 9 June 1999, respectively. The carbonaceous species were analyzed by the selective thermal manganese dioxide oxidation (TMO) method. In Sihwa, average OC and EC concentrations for the entire data set were measured to be 9.8 and 1.8 μg m⁻³, respectively. The OC concentrations were higher than those measured in other urban environments. The EC concentrations were lower than those of other urban environments. The OC/EC ratio measured at the Sihwa area was higher than those at other urban and rural environments. Backward trajectories of sampled air masses were performed to find out the sources of those higher OC/EC levels. Enrichment in the organic compounds during winter periods can be explained by the combination of primary local emissions from the industrial complex area and long-range transport of organic species from outside the Sihwa area. High OC values in June resulted from primary anthropogenic emissions and secondary organic aerosol formation rather than the atmospheric transport of organic compounds from the outside. In urban area of Seoul, the OC and EC concentrations in PM_2.5 during the summer were higher than those measured at other urban atmospheres. OC/EC ratios obtained in Seoul were lower than Sihwa. It can be concluded that carbonaceous species in Seoul were mainly emitted from primary anthropogenic sources.     

Evaluation of aerosol sources at European high altitude background sites with trajectory statistical methods

This study has investigated the influence of synoptic weather patterns and long-range transport episodes on the concentrations of several compounds related to different aerosol sources (EC, OC, SO₄^2?, Ca²⁺, Na⁺, K⁺, ²¹⁰Pb, levoglucosan and dicarboxylic acids) registered in PM10 or PM2.5 aerosol samples collected at three remote background sites in central Europe. Air mass back-trajectories arriving at these sites have been analysed by statistical methods. Firstly, air mass back-trajectories have been grouped into clusters. Each cluster corresponds to specific meteorological scenarios, which were extracted and discussed. Finally, redistributed concentration fields have been computed to identify the main potential source regions of the different key aerosol components. A marked seasonal pattern is observed in the occurrence of the different clusters, with fast westerly and northerly Atlantic flows during winter and weak circulation flows in summer. Spring and fall were characterised by advection of moderate flows from northeastern and eastern Europe. Significant inter-cluster differences were observed for concentrations of receptor aerosol components, with the highest concentrations of EC, OC, SO₄^2?, K⁺ and ²¹⁰Pb associated with local and mesoscale aerosol sources located over central Europe related to enhanced photochemical processes. Emissions produced by fossil fuel and biomass burning processes from the Baltic countries, Byelorussia, western regions of Russia and Kazakhstan in spring and fall also contribute to elevated levels of EC, OC, SO₄^2?, K⁺ and ²¹⁰Pb. In the summer period long-range transport episodes of mineral dust from North-African deserts were also frequently detected, which caused elevated concentrations of coarse Ca²⁺ at sites. The baseline aerosol concentrations in central Europe at the high altitude background sites were registered in winter, with the exception of coarse Na⁺. While the relatively high concentrations of Na⁺ can be explained by sea salt advected from the Atlantic, the low levels of other aerosol components are caused by efficient aerosol scavenging associated to advections of Atlantic air masses, as well as lower emissions of these species over the Atlantic compared to those over the European continent and very limited vertical air mass exchange over the continent.     

Characteristics of vertical profiles and sources of PM2.5, PM10 and carbonaceous species in Beijing

In August 2003 during the anticipated month of the 2008 Beijing Summer Olympic Games, we simultaneously collected PM₁₀ and PM_2.5 samples at 8, 100, 200 and 325 m heights up a meteorological tower and in an urban and a suburban site in Beijing. The samples were analysed for organic carbon (OC) and elemental carbon (EC) contents. Particulate matter (PM) and carbonaceous species pollution in the Beijing region were serious and widespread with 86% of PM_2.5 samples exceeding the daily National Ambient Air Quality Standard of the USA (65 μg m⁻³) and the overall daily average PM₁₀ concentrations of the three surface sites exceeding the Class II National Air Quality Standard of China (150 μg m⁻³). The maximum daily PM_2.5 and PM₁₀ concentrations reached 178.7 and 368.1 μg m⁻³, respectively, while those of OC and EC reached 22.2 and 9.1 μg m⁻³ in PM_2.5 and 30.0 and 13.0 μg m⁻³ in PM₁₀, respectively. PM, especially PM_2.5, OC and EC showed complex vertical distributions and distinct layered structures up the meteorological tower with elevated levels extending to the 100, 200 and 300 m heights. Meteorological evidence suggested that there exist fine atmospheric layers over urban Beijing. These layers were featured by strong temperature inversions close to the surface (<50 m) and more stable conditions aloft. They enhanced the accumulation of pollutants and probably caused the complex vertical distributions of PM and carbonaceous species over urban Beijing. The built-up of PM was accompanied by transport of industrial emissions from the southwest direction of the city. Emissions from road traffic and construction activities as well as secondary organic carbon (SOC) are important sources of PM. High OC/EC ratios (range of 1.8–5.1 for PM_2.5 and 2.0–4.3 for PM₁₀) were found, especially in the higher levels of the meteorological tower suggesting there were substantial productions of SOC in summer Beijing. SOC is estimated to account for at least 33.8% and 28.1% of OC in PM_2.5 and PM₁₀, respectively, with higher percentages at the higher levels of the tower.     

Loading Effect Correction for Real-Time Aethalometer Measurements of Fresh Diesel Soot

Abstract

In this study, a correction was developed for the aethalometer to measure real-time black carbon (BC) concentrations in an environment dominated by fresh diesel soot. The relationship between the actual mass-specific absorption coefficient for BC and the BC-dependent attenuation coefficients was determined from experiments conducted in a diesel exposure chamber that provided constant concentrations of fine particulate matter (PM; PM_2.5; PM <2.5 µm in aerodynamic diameter) from diesel exhaust. The aethalometer reported BC concentrations decreasing with time from 48.1 to 31.5 µg m^?3when exposed to constant PM_2.5concentrations of 55 ± 1 µg m^?3and b_scat= 95 ± 3 Mm^?1from diesel exhaust. This apparent decrease in reported light-absorbing PM concentration was used to derive a correction K(ATN) for loading of strong light-absorbing particles onto or into the aethalometer filter tape, which was a function of attenuation of light at 880 nm by the embedded particles.     

Seasonal and spatial trends in the sources of fine particle organic carbon in Israel,Jordan, and Palestine

A study of carbonaceous particulate matter (PM) was conducted in the Middle East at sites in Israel, Jordan, and Palestine. The sources and seasonal variation of organic carbon, as well as the contribution to fine aerosol (PM_2.5) mass, were determined. Of the 11 sites studied, Nablus had the highest contribution of organic carbon (OC), 29%, and elemental carbon (EC), 19%, to total PM_2.5 mass. The lowest concentrations of PM_2.5 mass, OC, and EC were measured at southern desert sites, located in Aqaba, Eilat, and Rachma. The OC contribution to PM_2.5 mass at these sites ranged between 9.4% and 16%, with mean annual PM_2.5 mass concentrations ranging from 21 to 25 ug m^?3. These sites were also observed to have the highest OC to EC ratios (4.1–5.0), indicative of smaller contributions from primary combustion sources and/or a higher contribution of secondary organic aerosol. Biomass burning and vehicular emissions were found to be important sources of carbonaceous PM in this region at the non-southern desert sites, which together accounted for 30%–55% of the fine particle organic carbon at these sites. The fraction of measured OC unapportioned to primary sources (1.4 μgC m^?3 to 4.9 μgC m^?3; 30%–74%), which has been shown to be largely from secondary organic aerosol, is relatively constant at the sites examined in this study. This suggests that secondary organic aerosol is important in the Middle East during all seasons of the year.     

Concentrations of aliphatic and polycyclic aromatic hydrocarbons in ambient PM2.5 and PM10 particulates in Doha,Qatar

Organic carbon (OC), elemental carbon (EC), and 90 organic compounds (36 polycyclic aromatic hydrocarbons [PAHs], 25 n-alkane homologues, 17 hopanes, and 12 steranes) were concurrently quantified in atmospheric particulate matter of PM_2.5 and PM₁₀. The 24-hr PM samples were collected using Harvard Impactors at a suburban site in Doha, Qatar, from May to December 2015. The mass concentrations (mean ± standard deviation) of PM_2.5 and PM₁₀ were 40 ± 15 and 145 ± 70 µg m^?3, respectively, exceeding the World Health Organization (WHO) air quality guidelines. Coarse particles comprised 70% of PM₁₀. Total carbonaceous contents accounted for 14% of PM_2.5 and 10% of PM₁₀ particulate mass. The major fraction (90%) of EC was associated with the PM_2.5. In contrast, 70% of OC content was found in the PM_2.5–10 fraction. The secondary OC accounted for 60–68% of the total OC in both PM fractions, indicating photochemical conversions of organics are much active in the area due to higher air temperatures and solar radiations. Among the studied compounds, n-alkanes were the most abundant group, followed by PAHs, hopanes, and steranes. n-Alkanes from C₂₅ to C₃₅ prevailed with a predominance of odd carbon numbered congeners (C₂₇–C₃₁). High-molecular-weight PAHs (5–6 rings) also prevailed, within their class, with benzo[b + j]fluoranthene (Bb + jF) being the dominant member. PAHs were mainly (80%) associated with the PM_2.5 fraction. Local vehicular and fugitive emissions were predominant during low-speed southeasterly winds from urban areas, while remote petrogenic/biogenic emissions were particularly significant under prevailing northwesterly wind conditions.

Implications: An unprecedented study in Qatar established concentration profiles of EC, OC, and 90 organic compounds in PM_2.5 and PM₁₀. Multiple tracer organic compounds for each source can be used for convincing source apportionment. Particle concentrations exceeded WHO air quality guidelines for 82–96% of the time, revealing a severe problem of atmospheric PM in Doha. Dominance of EC and PAHs in fine particles signifies contributions from combustion sources. Dependence of pollutants concentrations on wind speed and direction suggests their significant temporal and spatial variability, indicating opportunities for improving the air quality by identifying sources of airborne contaminants.     

Sources and characteristics of carbonaceous aerosol in two largest cities in Pearl River Delta Region,China

PM_2.5 samples were collected at five sites in Guangzhou and Hong Kong, Pearl River Delta Region (PRDR), China in both summer and winter during 2004–2005. Elemental carbon (EC) and organic carbon (OC) in these samples were measured. The OC and EC concentrations ranked in the order of urban Guangzhou > urban Hong Kong > background Hong Kong. Total carbonaceous aerosol (TCA) contributed less to PM_2.5 in urban Guangzhou (32–35%) than that in urban Hong Kong (43–57%). The reason may be that, as an major industrial city in South China, Guangzhou would receive large amount of inorganic aerosol from all kinds of industries, however, as a trade center and seaport, urban Hong Kong would mainly receive organic aerosol and EC from container vessels and heavy-duty diesel trucks. At Hong Kong background site Hok Tsui, relatively lower contribution of TCA to PM_2.5 may result from contributions of marine inorganic aerosol and inland China pollutant. Strong correlation (R²=0.76–0.83) between OC and EC indicates minor fluctuation of emission and the secondary organic aerosol (SOA) formation in urban Guangzhou. Weak correlation between OC and EC in Hong Kong can be related to the impact of the long-range transported aerosol from inland China. Averagely, secondary OC (SOC) concentrations were 3.8–5.9 and 10.2–12.8 μg m⁻³, respectively, accounting for 21–32% and 36–42% of OC in summer and winter in Guangzhou. The average values of 4.2–6.8% for SOA/ PM_2.5 indicate that SOA was minor component in PM_2.5 in Guangzhou.     

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.     

Elemental and organic carbon in urban canyon and background environments in Budapest,Hungary

As part of an international research project, aerosol samples were collected by several filter-based devices on Nuclepore polycarbonate membrane, Teflon membrane and quartz fibre filters over separate daylight periods and nights, and on-line aerosol measurements were performed by TEOM and aethalometer within an urban canyon (kerbside) and at a near-city background site in Budapest, Hungary from 23 April–5 May 2002. Aerosol masses in PM2.0, PM10–2.0, PM2.5, PM10 size fractions and of TSP were determined gravimetrically; atmospheric concentrations of organic (OC) and elemental carbon (EC) for PM2.5 (or PM2.0), PM10 fractions and for TSP were measured by thermal–optical transmission method. Repeatability of the mass determination by Nuclepore filters seems to be 5–6%. Collections on Teflon filters yielded smaller mass on average by 8(±12)% than that for the Nuclepore filters. Quartz filters overestimated the PM10 mass in comparison with the Nuclepore filters due primarily to sampling artefacts on average by 10(±16)% at the kerbside. Tandem filter set-ups were utilised for correcting the sampling artefacts for OC by subtraction method. At the kerbside, the aerosol mass was made up on average of 35(±4)% of organic matter (OM) in the PM10 fraction, while the contribution of OM to the PM2.5 mass was 43(±9)%. At the background, OM also accounted for 43(±13)% of the PM2.0 mass. On average, EC made up 14(±6)%, 7(±2)% and 4.5(±1.1)% of the mass in the PM2.5, PM10 fractions and TSP, respectively, at the kerbside; while its contribution was only 2.1(±0.5)% in the PM2.0 fraction in the near-city background. Temporal variability for PM mass, OC and EC concentrations was related to road traffic, local meteorology and long-range transport of air masses. It was concluded that a direct coupling between the atmospheric concentration levels and vehicle circulation can be identified within the urban canyon, nevertheless, the local meteorology in particular and long-range transport of air masses have much more influence on the air quality than changes in the source intensity of road traffic. Concentration ratios of OC/EC were evaluated, and the amount of secondary organic aerosol (SOA) was estimated by using EC as tracer for the primary OC emissions. Mean contribution and standard deviation of the SOA to the OM in the PM2.5 size fraction at the kerbside over daylight periods and nights were of 37(±18) and 46(±16)%, respectively.     

Laboratory and field evaluation of real-time and near real-time PM2.5 smoke monitors

ABSTRACT

Increases in large wildfire frequency and intensity and a longer fire season in the western United States are resulting in a significant increase in air pollution, including concentrations of PM_2.5 (particulate matter <2.5 µm in aerodynamic diameter) that pose significant health risks to nearby communities. During wildfires, government agencies monitor PM_2.5 mass concentrations providing information and actions needed to protect affected communities; this requires continuously measuring instruments. This study assessed the performance of seven candidate instruments: (1) Met One Environmental beta attenuation monitor (EBAM), (2) Met One ES model 642 (ES642), (3) Grimm Environmental Dust Monitor 164 (EDM), (4) Thermo ADR 1500 (ADR), (5) TSI DRX model 8543 (DRX), (6) Dylos 1700 (Dylos), and (7) Purple Air II (PA-II) in comparison with a BAM 1020 (BAM) reference instrument. With the exception of the EBAM, all candidates use light scattering to determine PM_2.5 mass concentrations. Our comparison study included environmental chamber and field components, with two of each candidate instrument operating next to the reference instrument. The chamber component involved 6 days of comparisons for biomass combustion emissions. The field component involved operating all instruments in an air monitoring station for 39.5 days with hourly average relative humidity (RH) ranging from 19% to 98%. Goals were to assess instrument precision and accuracy and effects of RH, elemental carbon (EC), and organic carbon (OC) concentrations. All replicate candidate instruments showed high hourly correlations (R² ≥ 0.80) and higher daily average correlations (R² ≥ 0.90), where all instruments correlated well (R² ≥ 0.80) with the reference. The DRX and Purple Air overestimated PM_2.5 mass concentrations by a factor of ~two. Differences between candidates and reference were more pronounced at higher PM_2.5 concentrations. All optical instruments were affected by high RH and by the EC/OC ratio. Equations to convert candidate instruments data to FEM BAM type data are provided to enhance the usability of data from candidate instruments.

Implications: This study tested the performance of seven candidate PM_2.5 mass concentration measuring instruments in two settings - environmental chamber and field. The instruments were tested to determine their suitability for use during biomass combustion events and the effects of RH, PM mass concentrations, and concentrations of EC and OC on their performance. The accuracy and precision of each monitor and effect of RH, PM concentration, EC and OC concentrations are varied. The data show that most of these candidate instruments are suitable for measuring PM_2.5 concentration during biomass combustions with a proper correction factor for each instrument type.     

Multi-year hourly PM2.5 carbon measurements in New York: Diurnal,day of week and seasonal patterns

Multi-year hourly measurements of PM_2.5 elemental carbon (EC) and organic carbon (OC) from a site in the South Bronx, New York were used to examine diurnal, day of week and seasonal patterns. The hourly carbon measurements also provided temporally resolved information on sporadic EC spikes observed predominantly in winter. Furthermore, hourly EC and OC data were used to provide information on secondary organic aerosol formation. Average monthly EC concentrations ranged from 0.5 to 1.4 μg m^?3 with peak hourly values of several μg m^?3 typically observed from November to March. Mean EC concentrations were lower on weekends (approximately 27% lower on Saturday and 38% lower on Sunday) than on weekdays (Monday to Friday). The weekday/weekend difference was more pronounced during summer months and less noticeable during winter. Throughout the year EC exhibited a similar diurnal pattern to NO_x showing a pronounced peak during the morning commute period (7–10 AM EST). These patterns suggest that EC was impacted by local mobile emissions and in addition by emissions from space heating sources during winter months. Although EC was highly correlated with black carbon (BC) there was a pronounced seasonal BC/EC gradient with summer BC concentrations approximately a factor of 2 higher than EC. Average monthly OC concentrations ranged from 1.0 to 4.1 μg m^?3 with maximum hourly concentrations of 7–11 μg m^?3 predominantly in summer or winter months. OC concentrations generally correlated with PM_2.5 total mass and aerosol sulfate and with NO_x during winter months. OC showed no particular day of week pattern. The OC diurnal pattern was typically different than EC except in winter when OC tracked EC and NO_x indicating local primary emissions contributed significantly to OC during winter at the urban location. On average secondary organic aerosol was estimated to account for 40–50% of OC during winter and up to 63–73% during summer months.     

Chemical speciation of PM emissions from heavy-duty diesel vehicles equipped with diesel particulate filter (DPF) and selective catalytic reduction (SCR) retrofits

Four heavy-duty diesel vehicles (HDDVs) in six retrofitted configurations (CRT^®, V-SCRT^®, Z-SCRT^®, Horizon, DPX and CCRT^®) and a baseline vehicle operating without after--treatment were tested under cruise (50 mph), transient UDDS and idle driving modes. As a continuation of the work by Biswas et al. [Biswas, S., Hu, S., Verma, V., Herner, J., Robertson, W.J., Ayala, A., Sioutas, C., 2008. Physical properties of particulate matter (PM) from late model heavy-duty diesel vehicles operating with advanced emission control technologies. Atmospheric Environment 42, 5622–5634.] on particle physical parameters, this paper focuses on PM chemical characteristics (Total carbon [TC], Elemental carbon [EC], Organic Carbon [OC], ions and water-soluble organic carbon [WSOC]) for cruise and UDDS cycles only. Size-resolved PM collected by MOUDI–Nano-MOUDI was analyzed for TC, EC and OC and ions (such as sulfate, nitrate, ammonium, potassium, sodium and phosphate), while Teflon coated glass fiber filters from a high volume sampler were extracted to determine WSOC. The introduction of retrofits reduced PM mass emissions over 90% in cruise and 95% in UDDS. Similarly, significant reductions in the emission of major chemical constituents (TC, OC and EC) were achieved. Sulfate dominated PM composition in vehicle configurations (V-SCRT^®-UDDS, Z-SCRT^®-Cruise, CRT^® and DPX) with considerable nucleation mode and TC was predominant for configurations with less (Z-SCRT^®-UDDS) or insignificant (CCRT^®, Horizon) nucleation. The transient operation increases EC emissions, consistent with its higher accumulation PM mode content. In general, solubility of organic carbon is higher (average ～5 times) for retrofitted vehicles than the baseline vehicle. The retrofitted vehicles with catalyzed filters (DPX, CCRT^®) had decreased OC solubility (WSOC/OC: 8–25%) unlike those with uncatalyzed filters (SCRT^®s, Horizon; WSOC/OC ～ 60–100%). Ammonium was present predominantly in the nucleation mode, indicating that ternary nucleation may be the responsible mechanism for formation of these particles.     

Attainment Flip-Flops and the Achievability of the Ozone Air Quality Standard

Abstract

This paper presents the results of the first reported study on fine particulate matter (PM) chemical composition at Salamanca, a highly industrialized urban area of Central Mexico. Samples were collected at six sites within the urban area during February and March 2003. Several trace elements, organic carbon (OC), elemental carbon (EC), and six ions were analyzed to characterize aerosols. Average concentrations of PM with aerodynamic diameter of less than 10 μm (PM₁₀) and fine PM with aerodynamic diameter of less than 2.5 μm (PM_2.5) ranged from 32.2 to 76.6 μg m^-3 and 11.1 to 23.7 μg m^-3, respectively. OC (34%), SO₄ ⁼ (25.1%), EC (12.9%), and geological material (12.5%) were the major components of PM_2.5. For PM₁₀, geological material (57.9%), OC (17.3%), and SO₄ ⁼ (9.7%) were the major components. Coarse fraction (PM₁₀ –PM_2.5), geological material (81.7%), and OC (8.6%) were the dominant species, which amounted to 90.4%. Correlation analysis showed that sulfate in PM_2.5 was present as ammonium sulfate. Sulfate showed a significant spatial variation with higher concentrations to the north resulting from predominantly southwesterly winds above the surface layer and by major SO₂ sources that include a power plant and refinery. At the urban site of Cruz Roja it was observed that PM_2.5 mass concentrations were similar to the submicron fraction concentrations. Furthermore, the correlation between EC in PM_2.5 and EC measured from an aethalometer was r² = 0.710. Temporal variations of SO₂ and nitrogen oxide were observed during a day when the maximum concentration of PM_2.5 was measured, which was associated with emissions from the nearby refinery and power plant. From cascade impactor measurements, the three measured modes of airborne particles corresponded with diameters of 0.32, 1.8, and 5.6 μm.     

Quantitative ED-EPMA combined with morphological information for the characterization of individual aerosol particles collected in Incheon,Korea

A quantitative single-particle analytical technique, called low-Z particle electron probe X-ray microanalysis, combined with the utilization of their morphological information on individual particles, was applied to characterize six aerosol samples collected in one Korean city, Incheon, during March 9–15, 2006. The collected supermicron aerosol particles were classified based on their chemical species and morphology on a single-particle basis. Many different particle types were identified and their emission source, transport, and reactivity in the air were elucidated. In the samples, particles in the “soil-derived particles” group were the most abundant, followed by “reacted sea-salts”, “reacted CaCO₃-containing particles”, “genuine sea-salts”, “reacted sea-salts + others”, “Fe-containing particles”, “anthropogenic organics”, (NH₄)₂SO₄, “K-containing particles”, and “fly ash”. The application of this single-particle analysis, fully utilizing their chemical compositional and morphological data of individual particles, clearly revealed the different characteristics of the six aerosol samples. For samples S3 and S5, which were sampled during two Asian dust storm events, almost all particles were of soil origin that had not experienced chemical modification and that did not entrain sea-salts during their long-range transport. For sample S1, collected at an episodic period of high PM₁₀ concentration and haze, anthropogenic, secondary, and soil-derived particles emitted from local sources were predominant. For samples S2, S4, and S6, which were collected on average spring days with respect to their PM₁₀ concentrations, marine originated particles were the most abundant. Sample S2 seems to have been strongly influenced by emissions from the Yellow Sea and Korean peninsula, sample S4 had the minimum anthropogenic influence among the four samples collected in the absence of any Asian dust storm event, and sample S6 seems to have entrained air pollutants that had been transported from mainland China over the Yellow Sea to Korea.     

Carbonaceous aerosol over a Pinus taeda forest in Central North Carolina,USA

Organic aerosol is the least understood component of ambient fine particulate matter (PM_2.5). In this study, organic and elemental carbon (OC and EC) within ambient PM_2.5 over a three-year period at a forested site in the North Carolina Piedmont are presented. EC exhibited significant weekday/weekend effects and less significant seasonal effects, in contrast to OC, which showed strong seasonal differences and smaller weekend/weekday effects. Summer OC concentrations are about twice as high as winter concentrations, while EC was somewhat higher in the winter. OC was highly correlated with EC during cool periods when both were controlled by primary combustion sources. This correlation decreased with increasing temperature, reflecting higher contributions from secondary organic aerosol, likely of biogenic origin. PM_2.5 radiocarbon data from the site confirms that a large fraction of the carbon in PM_2.5 is indeed of biogenic origin, since modern (non-fossil fuel derived) carbon accounted for 80% of the PM_2.5 carbon over the course of a year. OC and EC exhibited distinct diurnal profiles, with summertime OC peaking in late evening and declining until midday. During winter, OC peaked during the early morning hours and again declined until midday. Summertime EC peaked during late morning hours except on weekends. Wintertime EC often peaked in late PM or early AM hours due to local residential wood combustion emissions. The highest short term peaks in OC and EC were associated with wildfire events. These data corroborate recent source apportionment studies conducted within 20 km of our site, where oxidation products of isoprene, α-pinene, and β-caryophyllene were identified as important precursors to organic aerosols. A large fraction of the carbon in rural southeastern ambient PM_2.5 appears to be of biogenic origin, which is probably difficult to reduce by anthropogenic controls.     

PM composition and source reconciliation in Mexico City

PM_2.5 and PM₁₀ were collected during 24-h sampling intervals from March 1st to 31st, 2006 during the MILAGRO campaign carried out in Mexico City's northern region, in order to determine their chemical composition, oxidative activity and the estimation of the source contributions during the sampling period by means of the chemical mass balance (CMB) receptor model. PM_2.5 concentrations ranged from 32 to 70 μg m⁻³ while that of PM10 did so from 51 to 132 μg m⁻³. The most abundant chemical species for both PM fractions were: OC, EC, SO₄²⁻, NO₃⁻, NH₄⁺, Si, Fe and Ca. The majority of the PM mass was comprised of carbon, up to about 52% and 30% of the PM2.5 and PM10, respectively. PM2.5 constituted more than 50% of PM10. The redox activity, assessed by the dithiothreitol (DTT) assay, was greater for PM_2.5 than for PM₁₀, and did not display significant differences during the sampling period. The PM_2.5 source reconciliation showed that in average, vehicle exhaust emissions were its most important source in an urban site with a 42% contribution, followed by re-suspended dust with 26%, secondary inorganic aerosols with 11%, and industrial emissions and food cooking with 10% each. These results had a good agreement with the Emission Inventory. In average, the greater mass concentration occurred during O₃S that corresponds to a wind shift initially with transport to the South but moving back to the North. Taken together these results show that PM chemical composition, oxidative potential, and source contribution is influenced by the meteorological conditions.     

Carbon content of atmospheric aerosols in a residential area during the wood combustion season in Sweden

Carbonaceous aerosol particles were observed in a residential area with wood combustion during wintertime in Northern Sweden. Filter samples were analyzed for elemental carbon (EC) and organic carbon (OC) content by using a thermo-optical transmittance method. The light-absorbing carbon (LAC) content was determined by employing a commercial Aethalometer and a custom-built particle soot absorption photometer. Filter samples were used to convert the optical signals to LAC mass concentrations. Additional total PM₁₀ mass concentrations and meteorological parameters were measured. The mean and standard deviation mass concentrations were 4.4±3.6 μg m⁻³ for OC, and 1.4±1.2 μg m⁻³ for EC. On average, EC accounted for 10.7% of the total PM₁₀ and the contribution of OC to the total PM₁₀ was 35.4%. Aethalometer and custom-built PSAP measurements were highly correlated (R²=0.92). The hourly mean value of LAC mass concentration was 1.76 μg m⁻³ (median 0.88 μg m⁻³) for the winter 2005–2006. This study shows that the custom-built PSAP is a reliable alternative for the commercial Aethalometer with the advantage of being a low-cost instrument.     

Correlations between fine particulate matter (PM2.5) and meteorological variables in the United States: Implications for the sensitivity of PM2.5 to climate change

We applied a multiple linear regression (MLR) model to study the correlations of total PM_2.5 and its components with meteorological variables using an 11-year (1998–2008) observational record over the contiguous US. The data were deseasonalized and detrended to focus on synoptic-scale correlations. We find that daily variation in meteorology as described by the MLR can explain up to 50% of PM_2.5 variability with temperature, relative humidity (RH), precipitation, and circulation all being important predictors. Temperature is positively correlated with sulfate, organic carbon (OC) and elemental carbon (EC) almost everywhere. The correlation of nitrate with temperature is negative in the Southeast but positive in California and the Great Plains. RH is positively correlated with sulfate and nitrate, but negatively with OC and EC. Precipitation is strongly negatively correlated with all PM_2.5 components. We find that PM_2.5 concentrations are on average 2.6 μg m^?3 higher on stagnant vs. non-stagnant days. Our observed correlations provide a test for chemical transport models used to simulate the sensitivity of PM_2.5 to climate change. They point to the importance of adequately representing the temperature dependence of agricultural, biogenic and wildfire emissions in these models.     

Carbonaceous aerosol characteristics in outdoor and indoor environments of Nanchang, China, during summer 2009

A study of carbonaceous aerosol was initiated in Nanchang, a city in eastern China, for the first time. Daily and diurnal (daytime and nighttime) PM2.5 (particulate matter with aerodynamic diameter < or =2.5 microm) samples were collected at an outdoor site and in three different indoor environments (common office, special printing and copying office, and student dormitory) in a campus of Nanchang University during summer 2009 (5-20 June). Daily PM10 (particulate matter with aerodynamic diameter < or =10 microm) samples were collected only at the outdoor site, whereas PM2.5 samples were collected at both indoor and outdoor sites. Loaded PM2.5 and PM10 samples were analyzed for organic and elemental carbon (OC, EC) by thermal/optical reflectance following the Interagency Monitoring of Protected Visual Environments-Advanced (IMPROVE-A) protocol. Ambient mass concentrations of PM10 and PM2.5 in Nanchang were compared with the air quality standards in China and the United States, and revealed high air pollution levels in Nanchang. PM2.5 accounted for about 70% of PM10, but the ratio of OC and EC in PM2.5 to that in PM10 was higher than 80%, which indicated that OC and EC were mainly distributed in the fine particles. The variations of carbonaceous aerosol between daytime and nighttime indicated that OC was released and formed more rapidly in daytime than in nighttime. OC/EC ratios were used to quantify secondary organic carbon (SOC). The differences in SOC and SOC/OC between daytime and nighttime were useful in interpreting the secondary formation mechanism. The results of (1) OC and EC contributions to PM2.5 at indoor sites and the outdoor site; (2) indoor-outdoor correlation of OC and EC; (3) OC-EC correlation; and (4) relative contributions of indoor and outdoor sources to indoor carbonaceous aerosol indicated that OC indoor sources existed in indoor sites, with the highest OC emissions in I2 (the special printing and copying office), and that indoor EC originated from outdoor sources. The distributions of eight carbon fractions in emissions from the printer and copier showed obviously high OC1 (>20%) and OC2 (approximately 30%), and obviously low EC1-OP (a pyrolyzed carbon fraction) (<10%), when compared with other sources.