Variations of Particle Size Distribution, Black Carbon, and Brown Carbon during a Severe Winter Pollution Event over Xi'an, China

Real-time particulate matter (PM) size distributions, 4-hour time resolution, PM2.5, carbonaceous materials, and their optical properties were measured during a severe pollution event in Xi'an, China High PM2.5 /PM10 ratios were observed on both pollution (0.83) and non-pollution (0.73) days, emphasizing the abundance of fine particles during sampling days. The particle number (PN) first peaked with a wide size range (30-100 nm) before morning rush hours (approximately 01:00-05:00) on pollution and non-pollution days, demonstrating that PN was governed by the accumulation of freshly emitted diesel particles and characterized by distinct aerosol condensation growth. By contrast, the second peak time and size range differed between pollution and non-pollution days because of different formation mechanisms The light-absorbing coefficients of both black carbon (BC, b(abs-880nm,BC)) and brown carbon (BrC, b(abs-370nm, BrC)) were high on pollution days and decreased to approximately half of those values on non-pollution days, indicating that the degree of light absorption is reduced by rain. The diurnal variation in b(abs-880nm, BC) pollution peaked with traffic on January 1 and 2. By contrast, it remained in relatively stable and high ranges (120-160 Mm(-1)) in the second period (January 3-5) without traffic peaks, illustrating that the dominant sources changed even during the same pollution period. High values of both b(abs-370nm, BrC) and b(abs-880nm,) (BC )coincided in the afternoon and evening due to emissions from primary sources, and abundant aqueous secondary organic carbon, respectively. A highly variable mass absorption coefficient of BrC also indicated the variety of fuel combustion sources of primary BrC in Xi'an

Experimental determination and modelling of the solubilities of sodium sulfate and potassium sulfate in sub- and supercritical water

In this work, the solubility data of 20 different inorganic compounds were correlated by 7 available empirical and semi-empirical models in literature. The division criteria of four influential factors (temperature, pressure, the range of solubility data and the number of data points) were established to evaluate the correlative capability and applicability of these models at different conditions. Also, a novel four-parameter semi-empirical model has been proposed. Furthermore, the solubilities of sodium sulfate and potassium sulfate in sub- and supercritical water were measured at temperatures and pressures ranging from 633.15 to 723.15 K and 18-26 MPa, respectively. The experimental data were correlated using the reported models and the proposed novel model. The obtained results indicated that Cp-model is the best to fit the solubilities of these sulfates. In addition, the proposed model also exhibits a good correlation performance for the salt's solubility behaviors

Long-term trends in chemical composition of precipitation at Lijiang, southeast Tibetan Plateau, southwestern China

1090 precipitation samples were collected between 1989 and 2006 from the Lijiang region, an internationally important tourist site in Yunnan province, southwestern China. All the samples were analyzed for pH, electrical conductivity, SO4 2&minus;, Cl&minus;, NO3 &minus;, Na+, Ca2+, Mg2+ and NH4 + concentrations. pH had a mean value of 6.08 and showed a slight increase as tourism developed between 1989 and 2006. SO4 2&minus; and Ca2+ were the dominant anion and cation, respectively. Most of the ions showed significantly increasing trends, especially Ca2+ and Mg2+, with the exception of NH4 + that had a clearly decreasing trend. As a result, the neutralization capacity of Ca2+ increased significantly, and the precipitation NP/AP (neutralizing potential index/ acidifying potential index) ratio increased. There was a significant correlation between the soil-derived cations Ca2+ and Mg2+, and significant correlation of SO4 2&minus; with Ca2+ and Mg2+. The sea-salt species Cl&minus; and Na+ was not well correlated. Using Na+ as a sea-salt tracer, non-sea-salt source fractions were calculated as SO4 2&minus;: 99.1%, Mg2+: 92.6% and Ca2+: 99.8%. Furthermore, about 95.4% of NO3 &minus; and 41.7% of SO4 2&minus; were contributed by anthropogenic sources, and 57.4% of SO4 2&minus; was contributed by soil/dust sources that had a remarkably strong relationship (r=0.65, pb0.01) with the number of tourists, suggesting that human activities in a tourism-oriented city increase atmospheric dust loading.</p

Optical characteristics and source apportionment of brown carbon in winterPM2.5 over Yulin in Northern China

In this study, daily PM2.5 samples were collected at an urban site in Yulin of Northern China during a winter season. Eight carbon fractions, 13 kinds of polycyclic aromatic hydrocarbons (PAHs), and nine water-soluble ions in PM2.5 were measured. The light-absorption characteristics of brown carbon (BrC) both in water and in methanol extracts were evaluated and quantified. The total quantified PAHs exhibited high concentrations (228.4 &plusmn; 52.6 ng m&minus;3), contributing 0.2% of the PM2.5 mass. High indeno[1,2,3-cd]pyrene/(indeno[1,2,3-cd]pyrene + benzo[ghi]-perylene) ratio but low NO3&minus;/SO42&minus; ratio revealed the important contribution of coal combustion to PM2.5. The absorption coefficient (babs) for methanol extracts measured at 365 nm averaged 27.5 &plusmn; 12.0 Mm&minus;1. Light absorption by methanol extracts exhibited strong wavelength dependence, with an average absorption &Aring;ngstr&ouml;m exponent of 5.2 in the 330&ndash;400 nm range. The mass absorption cross section (for methanol extracts averaged 1.4 &plusmn; 0.4 m2 g&minus;1 by normalizing babs measured at 365 nm to organic carbon mass. A relatively strong positive relationship between babs, methanol and benzo[a]pyrene as well as with six carbon fractions indicated the important contribution of coal burning to BrC. Source apportionment based on the positive matrix factorization receptor model and multiple linear regression showed that residential coal combustion accounted for 37.4% of babs365,methanol. The estimated relative radiative forcing by methanol-soluble organic carbon relative to elemental carbon was 36.9% at 300&ndash;400 nm

Size Differentiation of Individual Atmospheric Aerosol during Winter in Xi'an, China

Airborne particulate matter (including TSP, PM10, PM2.5, and PM1) were collected at an urban site in Xi&#39;an during winter 2010. Individual particles were analyzed using scanning electron microscopy and energy dispersive X-ray spectrometer (SEM-EDX). The morphologies, size distributions, and relative abundance of aerosol particles in each size were summarized. The monomodal particle size distribution was found in all the samples under different weather conditions, with the peaks located at less than 1.0 mu m. The majority of particles were composed of soot, mineral dust, and tar balls, with minor fly ash particles. Soot aggregates were the predominant species (in numbers), ranging from 56.6% in TSP on a sunny day to 86.3% in PM1 on a cloudy day, with an average of 73.2% in all the samples. The particle mass concentration and chemical composition, including water-soluble inorganic ions, elemental compositions, organic carbon (OC) and elemental carbon (EC) contents of 24-hr integrated PM2.5, were also subject to chemical bulk analysis. Soot was predominantly observed in the PM2.5 samples (from 74.7% to 82.7% in numbers), whereas EC accounted for only a small amount (&lt; 8%) of the PM2.5 mass. Corresponding to the mass concentrations of geological materials (29.2%, 44.5%, and 37.3% on sunny, cloudy, and hazy days), the number concentrations of mineral dust and fly ash particles on the sunny, cloudy, and hazy days were 14.6%, 7.1%, and 7.7%, respectively.</p

Stable carbon isotopes and levoglucosan for PM2.5 elemental carbon sourceapportionments in the largest city of Northwest China

Stable carbon isotopes provide information on aerosol sources, but no extensive long-term studies of these isotopes have been conducted in China, and they have mainly been used for qualitative rather than quantitative purposes. Here, 24 h PM2.5 samples (n = 58) were collected from July 2008 to June 2009 at Xi&#39;an, China. The concentrations of organic and elemental carbon (OC and EC), water-soluble OC, and the stable carbon isotope abundances of OC and EC were determined. In spring, summer, autumn and winter, the mean stable carbon isotope in OC (&delta;13COC) were &minus;26.4 &plusmn; 0.6, &minus;25.8 &plusmn; 0.7, &minus;25.0 &plusmn; 0.6 and &minus;24.4 &plusmn; 0.8&permil;, respectively, and the corresponding &delta;13CEC values were &minus;25.5 &plusmn; 0.4, &minus;25.5 &plusmn; 0.8, &minus;25.2 &plusmn; 0.7 and &minus;23.7 &plusmn; 0.6&permil;. Large &delta;13CEC and &delta;13COC values in winter can be linked to the burning coal for residential heating. Less biomass is burned during spring and summer than winter or fall (manifested in the levels of levoglucosan, i.e., 178, 85, 370, 935 ng m&minus;3 in spring, summer, autumn, and winter), and the more negative &delta;13COC in the warmer months can be explained by the formation of secondary organic aerosols. A levoglucosan tracer method combined with an isotope mass balance analysis indicated that biomass burning accounted for 1.6&ndash;29.0% of the EC, and the mean value in winter (14.9 &plusmn; 7.5%) was 7 times higher than summer (2.1 &plusmn; 0.4%), with intermediate values of 6.1 &plusmn; 5.6 and 4.5 &plusmn; 2.4% in autumn and spring. Coal combustion accounted for 45.9 &plusmn; 23.1% of the EC overall, and the percentages were 63.0, 37.2, 36.7, and 33.7% in winter, autumn, summer and spring respectively. Motor vehicles accounted for 46.6 &plusmn; 26.5% of the annual EC, and these contributed over half (56.7&ndash;61.8%) of the EC in all seasons except winter. Correlations between motor vehicle-EC and coal combustion-EC with established source indicators (B(ghi)P and As) support the source apportionment results. This paper describes a simple and accurate method for apportioning the sources of EC, and the results may be beneficial for developing model simulations as well as controlling strategies in future