Molecular distribution and seasonal variation of hydrocarbons in PM2.5 from Beijing during 2006

Normal (n)-alkanes and polycyclic aromatic hydrocarbons (PAHs) in PM2.5 were collected from Beijing in 2006 and analyzed using a thermal desorption-GC/MS technique. Annual average concentrations of n-alkanes and PAHs were 282 +/- 96 and 125 +/- 150 ng/m(3), respectively: both were highest in winter and lowest in summer. C-19-C-25 compounds dominated the n-alkanes while benzo[b]fluoranthene, benzo[e]pyrene, and phenanthrene were the most abundant PAHs. The n-alkanes exhibited moderate correlations with organic carbon (OC) and elemental carbon (EC) throughout the year, but the relationships between the PAHs, OC and EC differed between the heating and non-heating seasons. The health risks associated with PAHs in winter were more than 40 times those in spring and summer even though the PM2.5 loadings were comparable. Carbon preference index values (&lt;1.5) indicated that the n-alkanes were mostly from fossil fuel combustion. The ratios of indeno[123-cd]pyrene to benzo[ghi]pyrelene in summer and spring were 0.58 +/- 0.12 and 0.63 +/- 0.09, respectively, suggesting that the PAHs mainly originated from motor vehicles, but higher ratios in winter reflected an increased influence from coal, which is extensively burned for domestic heating. A comprehensive comparison showed that PAH pollution in Beijing has decreased in the past 10 years.</p

Spatial-temporal pattern and population driving force of land use change in Liupan Mountains region, southern Ningxia, China

The Liupan Mountains is located in the southern Ningxia Hui Autonomous Region of China, which forms an important dividing line between landforms and bio-geographic regions. The populated part of the Liupan Mountains region has suffered tremendous ecological damages over time due to population pressure, excessive demand and inappropriate use of agricultural land resources. In this paper, datasets of land use between 1990 and 2000 were obtained from Landsat TM imagery, and then spatial models were used to characterize landscape conditions. Also, the relationship between the population density and land use/cover change (LUCC) was analyzed. Results indicate that cropland, forestland, and urban areas have increased by 44,186ha, 9001ha and 1550ha, respectively while the grassland area has appreciably decreased by 54,025ha in the study period. The decrease in grassland was most notable. Of the grassland lost, 49.4% was converted into cropland. The largest annual land conversion rate in the study area was less than 2%. These changes are attributed to industrial and agricultural development and population growth. To improve the eco-economic conditions in the study region, population control, urbanization and development of an ecological friendly agriculture were suggested

Selected water-soluble organic compounds found in size-resolved aerosols collected from urban, mountain and marine atmospheres over East Asia

Primary (i.e. sugars and sugar-alcohols) and secondary (i.e. carboxylic acids) water-soluble organic compounds (WSOCs) in size-segregated aerosols from the urban and mountain atmosphere of China and from the marine atmosphere in the outflow region of East Asia were characterized on a molecular level. Levoglucosan is the most abundant compound among the quantified WSOCs in the urban and mountain atmosphere, whose concentration at the urban site was 1-2 orders of magnitude higher than that at the mountain and marine sites. In contrast, malic, succinic and phthalic acids were dominant among the measured WSOCs at the marine site. In the urban air, sugars except levoglucosan gave a bimodal size distribution with a large peak in fine range (&lt;2.1 mu m) and a small peak in coarse range (&gt;= 2.1 mu m) during winter, being opposite to those in spring. In contrast, these WSOCs at the mountain and marine sites dominated in the coarse range but diminished and even disappeared in the fine range. Geometric mean diameters (GMDs) of the measured WSOCs in the fine mode at the urban site were larger in winter than in spring. Levoglucosan and carboxylic acids except for azelaic and benzoic acids showed a larger GMD in the coarse mode at the marine site probably due to an increased hygroscopic growth.</p

Comparison of dicarboxylic acids and related compounds in aerosol samples collected in Xi'an, China during haze and clean periods

PM10 aerosols from Xi&#39;an, a mega city of China in winter and summer, 2009 were measured for secondary organic aerosols (SOA) (i.e., dicarboxylic acids (DCA), keto-carboxylic acids, and &alpha;-dicarbonyls), water-soluble organic (WSOC) and inorganic carbon (WSIC), elemental carbon (EC) and organic carbon (OC). Molecular compositions of SOA on haze and clean days in both seasons were compared to investigate their sources and formation mechanisms. DCA in the samples were 1843&plusmn;810ngm-3 in winter and 1259&plusmn;781ngm-3 in summer, respectively, which is similar and even higher than those measured in 2003. Oxalic acid (C2, 1162&plusmn;570ngm-3 in winter and 1907&plusmn;707ngm-3 in summer) is the predominant species of DCA, followed by t-phthalic (tPh) in winter and phthalic (Ph) in summer. Such a molecular composition is different from those in other Asian cities where succinic acid (C4) or malonic acid (C3) is the second highest species, which is mostly due to significant emissions from household combustion of coal and open burning of waste material in Xi&#39;an. Mass ratios of C2/diacids, diacids/WSOC, WSOC/OC and individual diacid-C/WSOC are higher on the haze days than on the clean days in both seasons, suggesting an enhanced SOA production under the haze condition. We also found that the haze samples are acidic while the clean samples are almost neutral. Such a difference in particle acidity is consistent with the enhanced SOA production, because acid-catalysis is an important aqueous-phase formation pathway of SOA. Gly/mGly mass ratio showed higher values on haze days than on clean day in both seasons. We comprehensively investigated the ratio in literature and found a consistent pattern. Based on our observation results and those documented data we proposed for the first time that concentration ratio of Gly/mGly can be taken as an indicator of aerosol ageing.</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

Molecular composition and size distribution of sugars, sugar-alcohols and carboxylic acids in airborne particles during a severe urban haze event caused by wheat straw burning

Molecular compositions and size distributions of water-soluble organic compounds (WSOC, i.e., sugars, sugar-alcohols and carboxylic acids) in particles from urban air of Nanjing, China during a severe haze event caused by field burning of wheat straw were characterized and compared with those in the summer and autumn non-haze periods. During the haze event levoglucosan (4030 ng m(-3)) was the most abundant compound among the measured WSOC, followed by succinic acid, malic acid, glycerol, arabitol and glucose, being different from those in the non-haze samples, in which sucrose or azelaic acid showed a second highest concentration, although levoglucosan was the highest. The measured WSOC in the haze event were 2-20 times more than those in the non-hazy days. Size distribution results showed that there was no significant change in the compound peaks in coarse mode (&gt;2.1 mu m) with respect to the haze and non-haze samples, but a large difference in the fine fraction (&lt;2.1 mu m) was found with a sharp increase during the hazy days mostly due to the increased emissions of wheat straw burning. Molecular compositions of organic compounds in the fresh smoke particles from wheat straw burning demonstrate that sharply increased concentrations of glycerol and succinic and malic acids in the fine particles during the haze event were mainly derived from the field burning of wheat straw, although the sources of glucose and related sugar-alcohols whose concentrations significantly increased in the fine haze samples are unclear. Compared to that in the fresh smoke particles of wheat straw burning an increase in relative abundance of succinic acid to levoglucosan during the haze event suggests a significant production of secondary organic aerosols during transport of the smoke plumes.</p

Molecular distribution and stable carbon isotopic compositions of dicarboxylic acids and related SOA from biogenic sources in the summertime atmosphere of Mt. Tai in the North China Plain

Molecular distributions and stable carbon isotopic (&delta;13C values) compositions of dicarboxylic acids and related secondary organic aerosols (SOA) in PM2:5 aerosols collected on a day/night basis at the summit of Mt. Tai (1534 m a.s.l.) in the summer of 2016 were analyzed to investigate the sources and photochemical aging process of organic aerosols in the forested highland region of the North China Plain. The molecular distributions of dicarboxylic acids and related SOA are characterized by the dominance of oxalic acid (C2), followed by malonic (C3), succinic (C4) and azelaic (C9) acids. The concentration ratios of C2 = C4, diacid-C = OC and C2 = total diacids are larger in the daytime than in the nighttime, suggesting that the daytime aerosols are more photochemically aged than those in the nighttime due to the higher temperature and stronger solar radiation. Both ratios of C2 = C4 (R2 &gt; 0:5) and C3 = C4 (R2 &gt; 0:5) correlated strongly with the ambient temperatures, indicating that SOA in the mountaintop atmosphere are mainly derived from the photochemical oxidation of local emissions rather than long-range transport. The mass ratios of azelaic acid to adipic acid (C9 = C6), azelaic acid to phthalic aid (C9 = Ph) and glyoxal to methylglyoxal (Gly = mGly) and the strong linear correlations of major dicarboxylic acids and related SOA (i.e., C2, C3, C4, !C2, Pyr, Gly and mGly) with biogenic precursors (SOA tracers derived from isoprene, &alpha;/&beta;-pinene and &beta;-caryophyllene) further suggest that aerosols in this region are mainly originated from biogenic sources (i.e., tree emissions). C2 concentrations correlated well with aerosol pH, indicating that particle acidity favors the organic acid formation. The stable carbon isotopic compositions (&delta;13C) of the dicarboxylic acids are higher in the daytime than in the nighttime, with the highest value (&minus;16:5 &plusmn; 1:9 &permil;) found for C2 and the lowest value (&minus;25:2 &plusmn; 2:7 &permil;) found for C9. An increase in &delta;13C values of C2 along with increases in C2 = Gly and C2 = mGly ratios was observed, largely due to the isotopic fractionation effect during the precursor oxidation process.</p

Day-night differences and seasonal variations of chemical species in PM10 over Xi'an, northwest China

To investigate day-night differences and seasonal variations of PM10 and its chemical composition in an urban environment in Xi&#39;an, northwest China, day- and nighttime PM10 mass and its chemical components including water-soluble ions (Na+, NH4 (+), K+, Mg2+, Ca2+, F-, Cl-, NO3 (-), and SO4 (2-)), organic carbon (OC), elemental carbon, and water-soluble organic carbon (WSOC) were measured on selected representative days from 20 December 2006 to 12 November 2007. Annual mean PM10 concentration in this city was five times of the China Ambient Air Quality Standard for annual average (70 mu g m(-3)). Carbonaceous fractions and water-soluble ions accounted for nearly one third and 12.4 %, respectively, of the annual mean PM10 mass. No dramatic day-night differences were found in the loadings of PM10 or its chemical components. Spring samples were highlighted by abundance of Ca2+, while the secondary aerosol species (SO4 (2-), NO3 (-), and NH4 (+)) and OC dominated in summer, autumn, and winter samples. Relatively low NO3 (-)/SO4 (2-) ratio suggested that stationary source emissions were more important than vehicle emissions in the source areas in this city. Strong relationships between WSOC and biomass markers (water-soluble K+, OC1, and OP) were observed in winter and autumn, indicating that WSOC was derived mainly from biomass burning in these seasons. This was also supported by analysis results on the biomass burning events. In contrast, poor correlations between WSOC and biomass markers were demonstrated in summer and spring, implying that WSOC was mainly formed as secondary organic carbon through photochemical activities.</p

Molecular Distribution and Stable Carbon Isotopic Composition of Dicarboxylic Acids, Ketocarboxylic Acids, and alpha-Dicarbonyls in Size-Resolved Atmospheric Particles From Xi'an City, China

Size-resolved airborne particles (9-stages) in urban Xi&#39;an, China, during summer and winter were measured for molecular distributions and stable carbon isotopic compositions of dicarboxylic acids, ketocarboxylic acids, and alpha-dicarbonyls. To our best knowledge, we report for the first time the size-resolved differences in stable carbon isotopic compositions of diacids and related compounds in continental organic aerosols. High ambient concentrations of terephthalic (tPh, 379 +/- 200 ng m(-3)) and glyoxylic acids (omega C-2, 235 +/- 134 ng m(-3)) in Xi&#39;an aerosols during winter compared to those in other Chinese cities suggest significant emissions from plastic waste burning and coal combustions. Most of the target compounds are enriched in the fine mode (&lt;2.1 mu m) in both seasons peaking at 0.7-2.1 mu m. However, summertime concentrations of malonic (C-3), succinic (C-4), azelaic (C-9), phthalic (Ph), pyruvic (Pyr), 4-oxobutanoic (omega C-4), and 9-oxononanoic (omega C-9) acids, and glyoxal (Gly) in the coarse mode (&gt;2.1 mu m) are comparable to and even higher than those in the fine mode (&lt;2.1 mu m). Stable carbon isotopic compositions of the major organics are higher in winter than in summer, except oxalic acid (C-2), omega C-4, and Ph. delta C-13 of C-2 showed a clear difference in sizes during summer, with higher values in fine mode (ranging from -22.8 parts per thousand to -21.9 parts per thousand) and lower values in coarse mode (-27.1 parts per thousand to -23.6 parts per thousand). The lower delta C-13 of C-2 in coarse particles indicate that coarse mode of the compound originates from evaporation from fine mode and subsequent condensation/adsorption onto pre-existing coarse particles. Positive linear correlations of C-2, sulfate and omega C-2 and their delta C-13 values suggest that omega C-2 is a key intermediate, which is formed in aqueous-phase via photooxidation of precursors (e.g., Gly and Pyr), followed by a further oxidation to produce C-2.</p

Comparison of abundances, compositions and sources of elements, inorganic ions and organic compounds in atmospheric aerosols from Xi'an and New Delhi, two megacities in China and India

Wintertime TSP samples collected in the two megacities of Xi&#39;an, China and New Delhi, India were analyzed for elements, inorganic ions, carbonaceous species and organic compounds to investigate the differences in chemical compositions and sources of organic aerosols. The current work is the first time comparing the composition of urban organic aerosols from China and India and discussing their sources in a single study. Our results showed that the concentrations of Ca, Fe, Ti, inorganic ions, EC, PAHs and hopanes in Xi&#39;an are 1.3-2.9 times of those in New Delhi, which is ascribed to the higher emissions of dust and coal burning in Xi&#39;an. In contrast, Cl- levoglucosan, n-alkanes, fatty alcohols, fatty acids, phthalates and bisphenol A are 0.4-3.0 times higher in New Delhi than in Xi&#39;an, which is attributed to strong emissions from biomass burning and solid waste incineration. PAHs are carcinogenic while phthalates and bisphenol A are endocrine disrupting. Thus, the significant difference in chemical compositions of the above TSP samples may suggest that residents in Xi&#39;an and New Delhi are exposed to environmental hazards that pose different health risks. Lower mass ratios of octadecenoic acid/octadecanoic acid (C-18:1/C-18:0) and benzo(a)pyrene/benzo(e)pyrene (BaP/BeP) demonstrate that aerosol particles in New Delhi are photochemically more aged. Mass closure reconstructions of the wintertime TSP indicate that crustal material is the most abundant component of ambient particles in Xi&#39;an and New Delhi, accounting for 52% and 48% of the particle masses, respectively, followed by organic matter (24% and 23% in Xi&#39;an and New Delhi, respectively) and secondary inorganic ions (sulfate, nitrate plus ammonium, 16% and 12% in Xi&#39;an and New Delhi, respectively).</p