Characterization and source apportionment of aerosol light extinction in Chengdu, southwest China

To investigate aerosol properties in the Sichuan Basin of China, field aerosol sampling was carried out in Chengdu, China during four one-month periods, each in a different season in 2011. Aerosol scattering coefficient (b(sp)) at dry (RH&lt;40%) and wet (40% &lt; RH&lt;90%) conditions and aerosol absorption coefficient (b(ap)) were measured. Additionally, daily PM2.5 and PM10 samples were also collected. PM2.5 samples were subject to chemical analysis for various chemical components including major water-soluble ions, organic and elemental carbon (OC and EC), trace elements, as well as anhydrosugar Levoglucosan (LG) and Mannosan (MN). A multiple linear regression analysis was applied to the measured dry b(sp) against (NH4)(2)SO4, NH4NO3, organic mass (OM), fine soil (FS), and coarse mass (CM, PM2.5-10), and to the measured b(ap) against EC in all the four seasons to evaluate the impact of individual chemical components of PM2.5 and CM on aerosol light extinction (b(ext) = b(sp) + b(ap)). Mass scattering efficiency (MSE) and mass absorption efficiency (MAE) of the individual chemical components of PM2.5 were estimated based on seasonal regression equations and were then used for estimating b(ext). The annual b(sp), b(ap) and single scattering albedo (SSA) at dry conditions were 456 +/- 237 Mm(-1), 96 +/- 48 Mm(-1) and 0.82 +/- 0.05, respectively. The annual average b(sp) at ambient conditions estimated through hygroscopic curve of aerosol (f(RH)) was 763 +/- 415 Mm(-1), which was 1.7 times of the dry b(sp). The annual average SSA at ambient conditions also increased to 0.88 +/- 0.04. The estimated dry b(ext) was only 2 +/- 9% higher than the measurements and the estimated ambient bext from individual chemical components was only 1 +/- 10% lower, on an annual basis, than that estimated from using f(RH). Secondary inorganic aerosols, coal combustion, biomass burning, iron and steel industry, Mo-related industry, soil dust, and CM to b(ext) were estimated to account for 41 +/- 19%, 18 +/- 12%, 14 +/- 13%, 13 +/- 11%, 5 +/- 4%, 5 +/- 7% and 4 +/- 3%, respectively, of the estimated ambient b(ext).</p

Chemical composition of PM2.5 in an urban environment in Chengdu, China: Importance of springtime dust storms and biomass burning

Daily PM2.5 samples were collected in Chengdu, a megacity in southwest China, for a period of one month in every season during 2009-2010. Mass concentrations of water-soluble inorganic ions, organic carbon (OC), elemental carbon (EC), levoglucosan (LC), water soluble organic carbon (WSOC), and elements were determined to identify the chemical characteristics and potential sources of PM2.5. The data obtained in spring were discussed in detail to explore the impacts of dust storms and biomass burning on the chemical aerosol properties. The daily PM2.5 mass concentrations ranged from 49.2 to 425.0 mu g m(-3) with an annual average of 165.1 +/- 85.1 mu g m(-3). The highest seasonal average of PM2.5 concentrations was observed in the winter (225.5 +/- 73.2 mu g m(-3)) and the lowest in the summer (113.5 +/- 39.3 mu g m(-3)). Dust storm influence was observed only during the spring, while biomass burning activities occurred frequently in late spring and early summer. In the spring season, water-soluble ions, total carbonaceous aerosols, and the sum of the dominant elements (Al, Si, Ca, Ti, Fe, Mn, Zn, Pb, and Cu) accounted for 30.0 +/- 9.3%, 38.6 +/- 11.4%, and 6.2 +/- 5.3%, respectively, of the total PM2.5 mass. Crustal element levels evidently increased during the dust storm episode and LG, OC, WSOC, Cl- and K+ concentrations increased by a factor of 2-7 during biomass burning episodes. Using the Positive Matrix Factorization (PMF) receptor model, four sources for spring aerosols were identified, including secondary sulfate and nitrate, motor vehicle emissions, soil dust, and biomass burning. The four sources were estimated to contribute 24.6%, 18.8%, 23.6% and 33.0%, respectively, to the total PM2.5 mass.</p

Characterization of fine particulate black carbon in Guangzhou, a megacity of South China

Continuous measurement of fine particulate black carbon (BC) was conducted at an urban site of Guangzhou in South China from December 2007 to December 2008. The daily average BC concentrations ranged from 0.6 to 20.5 mu g m(-3), with an average value of 4.7 mu g m(-3), which was substantially higher than those observed in the urban areas of other developed countries. Diurnal fluctuations of BC were marked with two peaks, one in the morning rush hour (08:00 LT) and the other in the late evening hour (21:00-22:00 LT), while the lowest BC concentrations were observed in the afternoon. Ambient BC concentrations displayed significant seasonal and diurnal variations with higher values in winter and spring, followed by lower concentrations during autumn and summer. Wind speed, wind direction and temperature were important meteorological factors that affected BC concentrations. A clearly negative correlation (r=-0.50, p&lt;0.01) between BC concentrations and wind speed was found during the study period. A specific investigation was conducted to determine the relationship between optical BC and thermal-optical-reflectance elemental carbon (TOR EC) in distinct seasons. Although significant correlations between BC and EC were obtained (r&gt;0.92, p&lt;0.01), the regression slopes (Delta BC/Delta EC) slightly deviated from each other with values of 0.79, 1.18, and 0.81 in winter, spring and summer, respectively, possibly due to the distinct mixing states and source variations in different seasons. The calculated experimental attenuation coefficient showed a higher value (19.3 m(2) g(-1)) in Guangzhou than the one recommended for typical Aethalometer measurements.</p

Characteristics and applications of size-segregated biomass burningtracers in China's Pearl River Delta region

Biomass burning activities in China are ubiquitous and the resulting smoke emissions may pose considerable threats to human health and the environment. In the present study, size-segregated biomass burning tracers, including anhydrosugars (levoglucosan (LG) and mannosan (MN)) and nonsea-salt potassium (nss-K&thorn;), were determined at an urban and a suburban site in the Pearl River Delta (PRD) region. The size distributions of biomass burning tracers were generally characterized by a unimodal pattern peaking in the particle size range of 0.44e1.0 mm, except for MN during the wet season, for which a bimodal pattern (one in fine and one in coarse mode) was observed. These observed biomass burning tracers in the PRD region shifted towards larger particle sizes compared to the typical size distributions of fresh biomass smoke particles. Elevated biomass burning tracers were observed during the dry season when biomass burning activities were intensive and meteorological conditions favored the transport of biomass smoke particles from the rural areas in the PRD and neighboring areas to the sampling sites. The fine mode biomass burning tracers significantly correlated with each other, confirming their common sources. Rather high DLG/DMN ratios were observed at both sites, indicating limited influence from softwood combustion. High Dnss-K&thorn;/DLG ratios further suggested that biomass burning aerosols in the PRD were predominately associated with burning of crop residues. Using a simplified receptor-oriented approach with an emission factor of 0.075 (LG/TC) obtained from several chamber studies, average contributions of biomass burning emissions to total carbon in fine particles were estimated to be 23% and 16% at the urban and suburban site, respectively, during the dry season. In contrast, the relative contributions to total carbon were lower than 8% at both sites during the wet season.</p

PM2.5 and PM10-2.5 chemical composition and source apportionmentnear a Hong Kong roadway

Twenty-four-hour PM2.5 and PM10 samples were collected simultaneously at a highly trafficked roadside site in Hong Kong every sixth day from October 2004 to September 2005. The mass concentrations of PM2.5, PM10-2.5 (defined as PM10 &minus; PM2.5), organic carbon (OC), elemental carbon (EC), water-soluble ions, and up to 25 elements were determined. Investigation of the chemical compositions and potential sources revealed distinct differences between PM2.5 and PM10-2.5. The annual average mass concentrations were 55.5 &plusmn; 25.5 and 25.9 &plusmn; 15.7 g/m3 for PM2.5 and PM10-2.5, respectively. EC, OM (OM = OC &times; 1.4), and ammonium sulfate comprised over &sim;82% of PM2.5, accounting for &sim;29%, &sim;27%, and &sim;25%, respectively, of the PM2.5 mass. Low OC/EC ratios (less than 1) for PM2.5 suggested that fresh diesel-engine exhaust was a major contributor. Seven sources were resolved for PM2.5 by positive matrix factorization (PMF) model, including vehicle emissions (&sim;29%), secondary inorganic aerosols (&sim;27%), waste incinerator/biomass burning (&sim;23%), residual oil combustion (&sim;10%), marine aerosols (&sim;6%), industrial exhaust (&sim;4%), and resuspended road dust (&sim;1%). EC and OM comprised only &sim;19% of PM10-2.5. The average OC/EC ratio of PM10-2.5 was 7.8 &plusmn; 14.2, suggesting that sources other than vehicular exhaust were important contributors. The sources for PM10-2.5 determined by the PMF model included &sim;20% traffic-generated resuspension (e.g., tire dust/brake linear/petrol evaporation), &sim;17% locally resuspended road dust, &sim;17% marine aerosols, &sim;12% secondary aerosols/field burning, and &sim;11% vehicle emissions.</p

Quantification of carbonate carbon in aerosol filter samples using a modified thermal/optical carbon analyzer (M-TOCA)

Measurement of carbon dioxide (CO2) gas evolved from acidification is a method to quantify carbonate carbon (CC) in aerosols collected on quartz fiber-filters. This paper describes the installation of an add-on device in a DRI Model 2001 Thermal Optical reflectance (TOR)/Thermal Optical Transmittance (TOT) Carbon Analyzer (M-TOCA) to facilitate a direct CC measurement. In each run, a maximum of 20 filter punches (each of 0.5 cm(2)) were acidified with 1 mL of 20% v/v phosphoric (V) acid in a vial under a 100% helium gas environment. The CO2 evolved was reduced to methane (CH4) and detected by a flame ionization detector (FID). The optimum reaction kinetics were obtained under an operational temperature of 40 degrees C and ultrasonic agitation. Method precisions were +/- 3.5% on average for carbonate standards ranging from 3.0 to 60.0 mu g and +/- 3.8% on average for ambient samples in masses ranging from 0.30 to 56.0 mu g respectively. Method accuracy was on average 91.9%, ranging from 81.4 to 102.1%. Minimum detection limit (MDL) of the M-TOCA method was 0.048 mu g cm(-2), corresponding to an ambient concentration of 0.098 mu g m(-3) for a sampled volume of air of 7.2 m(3). The MDL is &gt;22 times lower than the value obtained using the novel method with a regular TOCA. Comparison studies on standards and ambient samples have demonstrated that the two methods do not yield systematic differences in concentrations of the carbonate. The lower MDL value provided by the M-TOCA allows a simple, precise and accurate measurement for ambient samples having a low CC concentration.</p