Comparison and implications of PM2.5 carbon fractionsin different environments

The concentrations of PM2.5 carbon fractions in rural, urban, tunnel and remote environments were measured using the IMPROVE thermal optical reflectance (TOR) method. The highest OC1 and EC1 concentrations were found for tunnel samples, while the highest OC2, OC3, and OC4 concentrations were observed for urban winter samples, respectively. The lowest levels of most carbon fractions were found for remote samples. The percentage contributions of carbon fractions to total carbon (TC) were characterized by one peak (at rural and remote sites) and two peaks (at urban and tunnel sites) with different carbon fractions, respectively. The abundance of char in tunnel and urban environments was observed, which might partly be due to traffic-related tire-wear. Various percentages of optically scattering OC and absorbing EC fractions to TC were found in the four different environments. In addition, the contribution of heating carbon fractions (char and soot) indicated various warming effects per unit mass of TC. The ratios of OC/EC and char/soot at the sites were shown to be source indicators. The investigation of carbon fractions at different sites may provide some information for improving model parameters in estimating their radiative effects.</p

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

Indoor and Outdoor Chemical Components of PM2.5 in the Rural Areas ofNorthwestern China

A case study of indoor and outdoor fine particles (PM2.5) was undertaken for rural areas in northwestern China, and quantitative data was obtained on their chemical composition including carbon fractions, water soluble ions, and elements. OM (organic matter), sulfate, and geological material dominated PM2.5, followed by nitrate and ammonium, which accounted for 78&ndash;85% of the mass for indoor and outdoor environments. The variations of the carbon fractions indicated that four OC factions and EC1 were more abundant in winter than in summer. SO4 2&minus; contributions were the highest of the ionic species for indoor and outdoor environments (about 40% of total ions in winter and 53% in summer), followed by NO3 &minus; (about 23% in winter and 14% in summer). The integrated results from the ratios of K+/OC, K+/EC, and as well as the EF (enrichment factor) values for K, Cl, S and Pb, indicate that the biofuel contributions were significant in the rural area. The indoor/outdoor ratios and correlations of the components were also investigated. The results for the indoor and outdoor PM2.5 sources showed that biomass burning in summer was the dominant primary source (31% for indoor and 44% for outdoor), and those for winter were coal combustion (21% for indoor and 29% for outdoor) and biomass burning (24% for indoor and 16% for outdoor). Due to the local patterns of energy consumption, the discussion presented in this work could give implications for future strategies to improve rural air quality.</p

N-Alkanes and polycyclic aromatic hydrocarbons in total suspended particulates from the southeastern Tibetan Plateau: Concentrations, seasonal variations, and sources

Sixty-two suspended particle (TSP) samples were collected from Lulang on the southeastern Tibetan Plateau from July 2008 and July 2009 to investigate the concentrations, seasonal variations, and sources of n-alkanes and polycyclic aromatic hydrocarbons (PAHs). Samples were analyzed using thermal-deposition gas chromatography mass spectrometry. The concentrations of particulate total n-alkanes ranged from 0.10 to 21.83ngm-3, with an annual mean of 1.25ngm-3; the PAHs ranged from 0.06 to 2.53, with a mean of 0.59 ngm-3. Up to 70% of PAHs were 5- and 6-ring compounds. The n-alkanes and PAHs both showed higher concentrations in winter and lower concentrations in summer. Analyses of diagnostic ratios indicate that 6.4% to 58.9% (mean 24.9%) of the n-alkanes were from plant waxes. Source characterization studies, i.e. diagnostic ratio and positive factor matrix analysis, suggest that the PAHs were from biomass burning as well as from fossil fuel combustion. Backward trajectory analysis suggests that the biomass mass burning pollutants could be from South Asia and western China via long distance transport. The study contributes to a more comprehensive understanding of the concentrations, seasonal variations, and sources of n-alkanes and PAHs in a remote background area in Tibetan Plateau.</p

Characteristics of surface ozone at an urban site of Xi'an in Northwest China

Surface ozone concentrations in Xi&#39;an, China were monitored from March 23, 2008 to January 12, 2009 using the Model ML/EC9810 ozone analyzer. The daily average O(3) ranged from &lt;1 ppb to 64.2 ppbv with an annual average of 16.0 ppbv. The seasonal average of O(3) in summer (32.5 ppbv) was more than 10 times higher than that in winter (3.0 ppbv). A significant positive correlation was found between ozone concentration and ambient temperature, indicating that the intensity of solar radiation was one of the several major factors controlling surface ozone production. Using the NOAA HYSPLIT 4 trajectory model, the three longest O(3) pollution episodes were found to be associated with the high biogenic volatile organic carbon (BVOC) emissions from the vegetation of Qinling Mountains. No significant weekday and weekend difference in O(3) levels was detected due to the non-significant change in NO(x) emissions. O(3) depletion by NO emission directly emitted from vehicles, low oxygenated VOC concentrations, and low-level solar radiation caused by high aerosol loading all contributed to the low levels of O(3) found in Xi&#39;an compared to other cities and rural areas.</p

Chemical composition of PM2.5 at a high–altitude regional backgroundsite over Northeast of Tibet Plateau

Aerosol samples were collected from a site near Qinghai Lake (QHL) on the northeastern margin of the Tibetan Plateau (TP) to investigate PM2.5 mass levels and chemical composition, especially their seasonal patterns and sources. The PM2.5 ranged from 5.7 to 149.7&nbsp;&mu;g m&ndash;3, and it was predominately crustal material (-40% on average). The combined mass of eight water&ndash;soluble inorganic ions ranged from 1.0 to 41.5&nbsp;&mu;g m&ndash;3, with the largest contributions from SO42&ndash; NO3-, and Ca2+. Low abundances of organic carbon (OC, range: 1.0 to 8.2&nbsp;&mu;g m&ndash;3) and elemental carbon (EC, 0.2 to 2.3&nbsp;&mu;g m&ndash;3) were found in QHL. Weak seasonality in the OC/EC ratio (4.5&plusmn;2.0) indicated simple and stable sources for carbonaceous particles. The water&ndash;soluble ions, OC and EC accounted for ~30%, 10% and 2% of the PM2.5, respectively. Water&ndash;soluble organic carbon (WSOC, range: 0.5 to 4.3&nbsp;&mu;g m&ndash;3) accounted for 47.8% of the OC. Both OC and WSOC were positively correlated with water&ndash;soluble K+(r=0.70 and 0.73 respectively), an indicator of biomass burning. Higher WSOC and stronger correlations between WSOC and EC in spring and winter compared with summer and autumn are evidence for primary biomass burning aerosols. The concentrations of mass and major compositions were 2&ndash;10 times higher than those for some TP or continental background sites but much lower than urban areas. Compared with particles produced from burning yak dung (a presumptive source material), PM2.5 had higher SO42&ndash;/OC ratios. The higher ratios were presumed as a result of fossil fuel combustion. After excluding data for dust storms events, the relative percentages of OM, EC, K+, NH4+, NO3&ndash; and mineral dust showed little difference among seasons despite different monsoons dominated in four seasons; implying that the PM2.5 sources were relatively stable. The results from QHL evidently reflect regional cha racteristics of the aerosol.</p

Day-Night Differences, Seasonal Variations andSource Apportionment of PM10-Bound PAHs overXi’an, Northwest China

Day-night PM10-bound PAHs were studied at an urban site of Xi’an from 20 December 2006 to 28 October 2007. The annual mean concentration of nighttime PAHs (285.0 ng m−3) was higher than that in daytime (239.4 ng m−3). A significant difference of PAH concentrations between daytime and nighttime was found in autumn with a coefficient of divergence (CD) of 0.23 (significant level 0.2). However, no distinct difference was observed in other seasons (with CD values < 0.2), although the difference of PAHs partition capacity in PM10 between daytime and nighttime was significant in the four seasons. Remarkable seasonal variations were observed in the total PAH levels, with a highest mean concentration of 344.6 ng m−3 in winter and a lowest mean concentration of 177 ng m−3 in summer. Positive matrix factorization results revealed that residential emission for heating is the major contributor of the elevated PAH levels in winter, accounting for 49% of the total PAH levels. The coal combustion including industrial and residential usage, contributed over 40% of the PAH emissions in PM10 of Xi’an during the one-year sampling period. These results can provide guidance for taking measures in reducing PAHs levels in the air

Light attenuation cross-section of black carbon in an urbanatmosphere in northern China

Fine particulate matter (PM2.5) samples were collected over two years in Xi&rsquo;an, China to investigate the relationships between the aerosol composition and the light absorption efficiency of black carbon (BC). Real-time light attenuation of BC at 880&nbsp;nm was measured with an aethalometer. The mass concentrations and elemental carbon (EC) contents of PM2.5 were obtained, and light attenuation cross-sections (&sigma;ATN) of PM2.5 BC were derived. The mass of EC contributed &sim;5% to PM2.5 on average. BC &sigma;ATN exhibited pronounced seasonal variability with values averaging 18.6, 24.2, 16.4, and 26.0&nbsp;m2/g for the spring, summer, autumn, and winter, respectively, while averaging 23.0&nbsp;m2/g overall. &sigma;ATN varied inversely with the ratios of EC/PM2.5, EC/[SO42&minus;], and EC/[NO3&minus;]. This study of the variability in &sigma;ATN illustrates the complexity of the interactions among the aerosol constituents in northern China and documents certain effects of the high EC, dust, sulfate and nitrate loadings on light attenuation.</p

Elemental profiles and signatures of fugitive dusts from Chinese deserts

Elemental profiles were determined for size-separated fugitive dust particles produced from Chinese desert and gobi soils. Seventeen surface soil samples from six Chinese deserts were collected, composited, resuspended, and sampled through TSP, PM10, and PM2.5 inlets onto Teflon&reg; filters, which were analyzed for twenty-six elements. Two major dust sources could be distinguished based on differences in crustal and enriched elements-the northwestern (NW) region (Taklimakan Desert, Xinjiang Gobi, and Anxinan Gobi) and northern (N) region (Ulan Buh Desert, Central Inner Mongolia Desert, and Erenhot Gobi). The N sources showed lower concentrations of mineral elements (Fe, K, Na, Ti, Mn, Cr, and Rb in PM10, and Fe, K, Ti, Mn, Co, and V in PM2.5) and higher levels of contaminants (S, Zn, Mo, Cu, Cr, Pb, Cd, and As) than the NW ones, especially in PM2.5. Enrichment factors for Cu, Cr, Zn, Pb, As, Mo, and Cd calculated relative to the upper continental crust showed enrichments of one to two orders-of-magnitude, and they were much higher for N sources than NW ones, implying stronger anthropogenic impacts in north China. Aerosol elemental concentrations during dust events at Horqin, Beijing, and Xi&#39;an matched the mass percentages of mineral elements from their presumptive sources better than the alternative ones, validating the differences between the NW and N sources. Additionally, Na/S, Mg/S, Fe/Al, K/Al, Si/Fe, and Na/Al ratios were suggested to differentiate the two dust source regions. The elemental ratios of Ca/Al, K/Al, Fe/Al, and Ti/Fe in the source regions matched those in aerosols collected downwind, and they can be considered as possible source indicators.</p

Airborne particulate organic markers at the summit (2060 m,a.s.l.) of Mt. Hua in central China during winter: Implications for biofuel and coal combustion

Sugars, n-alkanes and PAHs in PM10 and size-segregated samples collected from the summit (2060 m, altitude) of Mt. Hua in Guanzhong Plain, central China during the winter of 2009 were characterized using a GC/MS technique. Concentrations of sugars, n-alkanes and PAHs in PM10 are 107&plusmn;52, 121&plusmn;63, 7.3&plusmn;3.4 ng m&minus;3, respectively. Levoglucosan and fossil fuel derived n-alkanes are more abundant in the air masses transported from southern China than in those from northern China with no spatial difference found for PAHs, suggesting that emissions from biomass burning and vehicle exhausts are more significant in southern part of the country. Dehydrated sugars, fossil fuel derived n-alkanes and PAHs presented a unimode size distribution, peaking at the size of 0.7&ndash;1.1 &mu;m, whereas non-dehydrated sugars and plant wax derived n-alkanes showed a bimodal pattern, peaking at 0.7&ndash;2.1 and 5.8&ndash;9.0 &mu;m, respectively. Principal component analysis showed that biofuel combustion plus plant emission is the most important source in Mt. Hua, being different from the cases in Chinese urban areas where fossil fuel combustion is the major source. By comparison with previous mountain and lowland observations and aircraft measurements we found that wintertime PAHs in China are still characterized by coal burning emissions especially in the inland regions, although in the country increasing rate of SO2 emission from coal combustion has decreased and emissions of vehicle exhaust has sharply increased.</p