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

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

Seasonal variations and chemical characteristics of sub-micrometer particles (PM1) in Guangzhou, China

Daily samples of ambient sub-micrometer particles (PM1, particles with an aerodynamic diameter &le; 1.0 &mu;m) were collected from July 2009 to April 2010 at an urban site over Guangzhou in southern China. Mass concentrations of water-soluble inorganic ions, organic carbon (OC) and elemental carbon (EC) were determined to characterize the chemical composition of PM1. The mass concentration of PM1 ranged from 14.6 &mu;g m&minus; 3 to 143.3 &mu;g m&minus; 3, with an annual mean value of 52.4 &plusmn; 27.3 &mu;g m&minus; 3. Seasonally-averaged PM1 concentrations decreased in the order winter &gt; autumn &gt; spring &gt; summer. The annual mean concentrations of OC and EC were 6.2 &plusmn; 3.5 and 5.0 &plusmn; 2.9 &mu;g m&minus; 3, respectively. The OC and EC concentrations were measured following the IMPROVE_A thermal/optical reflectance (TOR) protocol. Total carbonaceous aerosol (the sum of organic matter and elemental carbon) accounted for 23.0 &plusmn; 4.4% of PM1 mass. Clear seasonal variations in OC and EC suggested sources of these two constituents were remarkable difference among the four seasons. Seasonally averaged OC/EC ratios were 1.2, 1.7, 1.4, and 1.5, from spring to winter respectively. Low OC/EC ratios in comparison with other cities in China revealed that vehicle emissions play an important role in carbonaceous aerosol levels in Guangzhou. SO42 &minus;, NO3&minus; and NH4+ were the three major inorganic ions in PM1, collectively contributing 30.0% &plusmn; 6.3% of the PM1 mass. SO42 &minus; and NH4+ were both the highest in autumn and the lowest in summer. In contrast, NO3&minus; was the highest in winter. Sulfur oxidation ratio was positively correlated with solar radiation and O3, but negatively correlated with SO2. Nitrogen oxidation ratio was positively correlated with NO2, NH4+ and Cl&minus;, but showed a negative correlation with temperature. By applying the IMPROVE equation, PM1 mass was reconstructed and showed that (NH4)2SO4, NH4NO3, OM and EC accounted for (30.7 &plusmn; 11.4) %, (9.7 &plusmn; 5.2) %, (22.6 &plusmn; 5.0) % and (9.7 &plusmn; 2.3) % of PM1, respectively. Finally, source apportionment by positive matrix factorization revealed that (1) secondary aerosol and biomass burning, (2) diesel emissions, (3) gasoline emissions and sea salt, and (4) coal combustion were the greatest contributors to PM1.</p

Chemical profiles of urban fugitive dust over Xi'an in the south margin of the Loess Plateau, China

Urban fugitive dust samples were collected to determine the chemical profiles of fugitive dust over Xi&#39;an. Seventy eight samples were collected and divided into categories of paved road dust, construction dust, cement dust, and soil dust. Eighteen elements, including Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Ba, and Pb, and eight water-soluble inorganic ions, including Na+, Mg2+, Ca2+, NH4+, F-, Cl-, NO3- and SO42-, were measured. The most abundant elements in these urban dust samples were Al, Si, Ca, and Fe. Al, Si, K, and Ti and showed strong positive correlations with each other, indicating they are typical dust trace elements. In contrast, elements of Ca, Zn, As, and Pb had negative correlations to crustal elements. Si/Al, K/Al, Ti/Al, Mn/Al, and Fe/Al ratios varied insignificantly among these four samples types; these ratios are similar to the properties of loess, desert, and Gobi soil dust reported in previous studies. A significantly higher Ca/Al ratio was dominant in the chemical profile of the cement samples. In addition, high Pb/Al and Zn/Al ratios were detected in comparison with those in the Gobi soil, desert soil, and loess soil samples, which indicated that Pb/Al and Zn/Al ratios can be considered as markers of urban dust. Total water-soluble ions occupied only a small fraction (&lt;5%) in the urban fugitive soil samples indicating that most of the materials in the fugitive dust were insoluble. Ca2+ and SO42- were the most abundant ions in all samples. Most of the Ca and K in the fugitive soil samples were in insoluble phases, which differ significantly in comparison with combustion sources. A strong correlation was observed between Ca2+ and estimated CO32- levels indicating that most of Ca2+ was in the form of CaCO3 rather than other calcium minerals in Xi&#39;an fugitive dust.</p

On the potential high acid deposition in northeastern China

There is an acid deposition conundrum in China: contrary to conventional wisdom, extremely high ambient sulfate concentrations in northeastern China are not always accompanied by correspondingly high acidities. To investigate this discrepancy, data from two independent sets of in situ field measurements were analyzed along with Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite observations and Model for Ozone and Related chemical Tracers (MOZART) chemical transport model calculations. The field measurements included soluble aerosol ion concentrations and pH and particulate data from 11 cities, as well as pH measurement data from 74 sites in China. This study explores the basis for and the impacts of the large discrepancy in northeastern China between the major acidity precursors (SO2 and NOx) and measured acidity levels as indicated by pH values. There are extremely high SO2 emissions and ambient concentrations in northeastern China, while the corresponding acidity is unusually low (high pH) in this region. This is inconsistent with the usual situation where high-acidity precursor pollutants result in low pH (high acidity) values and acid rain conditions. In other regions, such as southern China and the United States, high SO2 concentrations are typically well correlated with high acidities. Using measured soluble particle measurements (including both positively and negatively charged ions), it is seen that there are high values of alkaline ions in northeastern China that play an important role in neutralizing acidity in this region. This result strongly suggests that the high alkaline concentrations, especially Ca2+, increase warm season pH values by about 0.5 in northern China, partially explaining the inconsistency between sulfate concentrations and acidity. This has a very important implication for acid rain mitigationespecially in northeastern China. However, there are additional issues pertaining to the precursor-acidity relationship that need further investigation. Why is it that the reduction in acidity due to the alkaline ions is only significant in summer? During winter, the measured alkaline ions play a much smaller role in explaining the discrepancy. The measured alkaline ions in this study were mostly obtained from particles in the PM2.5 range. However, the size of calcium particles is typically much largerextending well beyond 2.5 mu mand so a significant amount of calcium may be underestimated by PM2.5 measurements alone. The under-sampling of calcium particles is further exacerbated in that the sampling protocol excluded particle (and soluble ion and pH) measurements during dust storms. This all leads to the need for an improved understanding of pollutant-ion-particulate interactions in China, and their role in explaining the counter-intuitive conclusion that dust mitigation strategies in China could have the unintended consequence of exacerbating acid rain conditions.</p

Real-time measurements of PM2.5, PM10–2.5, and BC in an urban streetcanyon

A continuous dichotomous beta gauge monitor was used to characterize the hourly content of PM2.5, PM10&ndash;2.5, and Black Carbon (BC) over a 12-month period in an urban street canyon of Hong Kong. Hourly vehicle counts for nine vehicle classes and meteorological data were also recorded. The average weekly cycles of PM2.5, PM10&ndash;2.5, and BC suggested that all species are related to traffic, with high concentrations on workdays and low concentrations over the weekends. PM2.5 exhibited two comparable concentrations at 10:00&ndash;11:00 (63.4&nbsp;&mu;g/m3) and 17:00&ndash;18:00 (65.0&nbsp;&mu;g/m3) local time (LT) during workdays, corresponding to the hours when the numbers of diesel-fueled and gasoline-fueled vehicles were at their maximum levels: 3179 and 2907&nbsp;h&minus;1, respectively. BC is emitted mainly by diesel-fueled vehicles and this showed the highest concentration (31.2&nbsp;&mu;g/m3) during the midday period (10:00&ndash;11:00 LT) on workdays. A poor correlation was found between PM2.5 concentration and wind speed (R&nbsp;=&nbsp;0.51, P-value&nbsp;&gt;&nbsp;0.001). In contrast, the concentration of PM10&ndash;2.5 was found to depend upon wind speed and it increased with obvious statistical significance as wind speed increased (R&nbsp;=&nbsp;0.98, P-value&nbsp;&lt;&nbsp;0.0001).</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

Chemical characteristics of PM2.5 during dust storms and air pollution events in Chengdu, China

Daily fine particulate (PM2.5) samples were collected in Chengdu from April 2009 to February 2010 to investigate their chemical profiles during dust storms (DSs) and several types of pollution events, including haze (HDs), biomass burning (BBs), and fireworks displays (FDs). The highest PM2.5 mass concentrations were found during DSs (283.3 mu g/m(3)), followed by FDs (212.7 mu g/m(3)), HDs (187.3 mu g/m(3)), and BBs (130.1 mu g/m(3)). The concentrations of most elements were elevated during DSs and pollution events, except for BBs. Secondary inorganic ions (NO3-, SO42-, and NH4+) were enriched during HDs, while PM2.5 from BBs showed high K+ but low SO42-. FDs caused increases in K+ and enrichment in SO42-. Ca2+ was abundant in DS samples. Ion-balance calculations indicated that PM2.5 from HDs and FDs was more acidic than on normal days, but DS and BB particles were alkaline. The highest organic carbon (OC) concentration was 26.1 mu g/m(3) during FDs, followed by BBs (23.6 mu g/m(3)), HDs (19.6 mu g/m(3)), and DSs (18.8 mu g/m(3)). In contrast, elemental carbon. (EC) concentration was more abundant during HDs (10.6 mu g/m(3)) and FDs (9.5 mu g/m(3)) than during BBs (6.2 mu g/m(3)) and DSs (6.0 mu g/m(3)). The highest OC/EC ratios were obtained during BBs, with the lowest during HDs. SO42-/K+ and TCA/SO42- ratios proved to be effective indicators for differentiating pollution events. Mass balance showed that organic matter, SO42-, and NO3- were the dominant chemical components during pollution events, while soil dust was dominant during DSs.</p

Simulation and optimization of the post plasma-catalytic system for toluene degradation by a hybrid ANN and NSGA-II method

In this study, a post-non-thermal plasma (NTP)-catalytic system was developed for the removal of toluene over a series of MnCoOx/gamma-Al2O3 catalysts. The addition of the MnCoOx/gamma-Al2O3 catalysts markedly promoted the toluene removal efficiency, CO. yield, CO2 yield and energy yield (EY) compared with the plasma alone system. The 5 wt% MnCoOx/gamma-Al2O3 catalyst exhibited the best reaction performance, which could be attributed to the reducibility and surface active oxygen species of the catalyst. With artificial neural network (ANN), the effects of experimental parameters on the reaction performance of toluene degradation were modeled and analyzed; for this analysis, four parameters were considered, namely, discharge power, initial concentration of toluene, flow rate, and relative humidity. The results indicated that the predicted results fitted well with the experimental results. The discharge power was the most significant factor for the toluene removal efficiency and CO. yield, whereas the EY was the most influenced by the gas flow rate. A multi-objective optimization model was proposed to determine optimal experimental parameters, which was then solved using the non-dominating sorting genetic algorithm II (NSGA-II). The results revealed that the Pareto front obtained from the hybrid ANN and NSGA-II method provided a series of feasible and optimal process parameters for the post-NTP-catalytic system. This hybrid method also served as an effective tool to select process parameters according to application conditions and preferences

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