Hongmei Xu

Spatial and seasonal variations of PM2.5 mass and species during 2010 in Xi'an, China

PM2.5 mass and selected chemical species are measured in 24-h integrated PM2.5 samples collected simultaneously at the urban and rural regions of Xian (six sites in total), China in the four seasons of 2010. The analytes include organic carbon and elemental carbon (OC+EC = total carbon, TC), seven water-soluble inorganic ions (NH4(+), K(+), Mg(2+), Ca(2+), Cl(-), SO4(2-), NO3(-)) and six trace elements (Ti, Mn, Fe, Zn, As, Pb). The average PM2.5 mass for the entire measurement period is 142.6 ± 102.7 μg m(-3), which is more than four times that of the Chinese national ambient air quality standard. Spatial variations in PM2.5 mass are not pronounced. The PM2.5 mass and those species measured show a similar seasonal pattern in all six measurement sites, i.e., in the order of winter > autumn > spring > summer. The dominant PM2.5 composition is OC in winter, soil dust in spring, and sulfate, nitrate, and ammonium in summer and autumn. Seasonal variations of TC/PM2.5 and OC/EC ratios follow the PM2.5 changes. Seasonal distributions of (SO4(2-)+NO3(-)+NH4(+))/PM2.5 showed increase in autumn and decrease in winter, while NO3(-)/SO4(2-) ratios increased in autumn and decreased in summer. Eight main PM2.5 sources are identified based on the positive matrix factorization (PMF) analysis and emissions from fossil fuel combustion (traffic and coal burning) are founded to be the main source responsible for the fine particle pollution in Xian. In addition, a decreasing trend in OC/PM2.5 is observed in comparison with previous studies in Xian.

Characteristics and major sources of carbonaceous aerosols in PM2.5 from Sanya, China.

PM2.5 samples were collected in Sanya, China in summer and winter in 2012/2013. Organic carbon (OC), elemental carbon (EC), and non-polar organic compounds including n-alkanes (n-C14-n-C40) and polycyclic aromatic hydrocarbons (PAHs) were quantified. The concentrations of these carbonaceous matters were generally higher in winter than summer. The estimated secondary organic carbon (OCsec) accounted for 38% and 54% of the total organic carbon (TOC) in winter and summer, respectively. The higher value of OCsec in addition to the presences of photochemically-produced PAHs in summer supports that photochemical conversions of organics are much active at the higher air temperatures and with stronger intense solar radiation. Carbon preference index (CPI) and percent contribution of wax n-alkanes suggest that anthropogenic sources were more dominant than derivation from terrestrial plants in Sanya. Diagnostic ratios of atmospheric PAHs further indicate that there was a wide mix of pollution sources in winter while fossil fuel combustion was the most dominant in summer. Positive Matrix Factorization (PMF) analysis with 18 PAHs in the winter samples found that motor vehicle emissions and biomass burning were the two main pollution sources, contributing 37.5% and 24.6% of the total quantified PAHs, respectively.

Chemical profiles of urban fugitive dust PM2.5 samples in Northern Chinese cities

Urban fugitive dust PM2.5 samples were collected in 11 selected cities in North China, and 9 ions (SO4(2-), NO3(-), Cl(-), F(-), Na(+), NH4(+), K(+), Mg(2+), and Ca(2+)) and 22 elements (Si, Al, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Rb, Sr, Sn, Sb, Ba, and Pb) were determined to investigate chemical profiles of PM2.5. The coefficient of divergence (CD) was used to compare the similarities of the chemical profiles for fugitive dust among three regions in North China, and the results showed that their composition are quite similar. Total water soluble ions occupied 9.3% and 10.0% on average of road dust and construction dust, respectively, indicating that most of the materials in urban fugitive dust samples were insoluble. Ca(2+) was the most abundant cation and SO4(2-) dominated in anions. Soil dust loading was calculated to occupy 70.8% and 83.6% in road dust and construction dust, respectively. Ca, Si, Fe, and Al were the most abundant elements in all the samples, and Ca was absolutely the most abundant specie among the 22 detected elements in construction dust samples. Chemical species ratios were used to highlight the characteristics of urban fugitive dust by comparing with other types of aerosols. High Ca/Al ratio was a good marker to distinguish urban fugitive dust from Asian dust and Chinese loess. In addition, low K(+)/K and NO3(-)/SO4(2-), and high Zn/Al and Pb/Al ratios were good indicators to separate urban fugitive dust from desert dust, Chinese loess, or urban PM2.5 samples.

Methanol Extracted Brown Carbon in PM2.5 Over Xi’an, China: Seasonal Variation of Optical Properties and Sources Identification

Aerosol optical properties, including absorption coefficient (babs), absorption Ångström exponent (AAE), and mass absorption coefficient (MAC), of methanol extracts in PM2.5 samples were measured at an urban site in Xi’an, northwest China in a winter and summer season. Water soluble ions, organic carbon (OC), element carbon, eight carbon fractions, levoglucosan, and 13 polycyclic aromatic hydrocarbons were also determined to explore the sources of brown carbon (BrC) in PM2.5. babs at 365xa0nm wavelength showed a clear seasonal variation with much higher value in winter than summer. High levoglucosan and K+ concentrations in winter and their good correlations with babs inferred the important contribution of biomass burning to BrC. Good correlations between babs and OC1, OC2, OC3, or OP indicated the mixed sources of biomass burning and coal combustion for BrC. Relatively poor correlations were found between babs and indeno[1,2,3-cd]pyrene (IP) or Benzo[ghi]-perylene (BghiP), indicating limited contribution of vehicle exhaust to BrC. Seasonal distribution of AAE indicated that secondary organic carbon (SOC) BrC was mainly fresh SOC in winter but a mix of fresh and aged SOC in summer. MAC of BrC in winter was more than double of that in summer, suggesting that BrC from biomass burning and fresh SOC were stronger light absorbing in winter than the aged SOC in summer. A 7-wavelength Aethalometer model AE31 was used to evaluate the seasonal variations of babs for BrC (370xa0nm) and black carbon (BC) (880xa0nm). BrC and BC were both important in light absorption in winter, but BC prevailed over BrC in summer.

Optical source profiles of brown carbon in size-resolved particulate matter from typical domestic biofuel burning over Guanzhong Plain, China

In this study, both PM2.5 and size-resolved source samples were collected from a heated kang and an advanced stove to investigate the optical properties of brown carbon (BrC). The light-absorption coefficient (babs), the absorption Ångström exponent (AAE), and the mass absorption cross-section (MAC) of both water and methanol-extracted BrC were investigated. The methanol-extracted BrC (BrCmethanol) had higher light absorption than water-extracted BrC (BrCwater). The value of PM2.5 babs of BrCmethanol at 365nm (babs365,methanol) dramatically decreased from 64,669.8Mm-1 for straw burning in the heated kang to 1169.2Mm-1 for maize straw briquettes burning in the advanced stove at the same burning rate. The value of PM2.5 MAC for BrCmethanol at 365nm (MAC365,methanol) decreased from 1.8m2g-1 in the heated kang to 1.3m2g-1 in the advanced stove. For smoldering burning in the heated kang, babs365,methanol, MAC365,methanol, and K+ showed a unimodal distribution that peaked at sizes <0.4μm. However, the babs365,methanol and MAC365,methanol size distributions of the briquette burning in the advanced stove showed a bimodal pattern, with a large peak at sizes <0.4μm and a minor peak in the size range of 4.7-5.8μm. The babs365,methanol value for sizes <0.4μm (277.4Mm-1) was only 12.3% compared to those obtained from the heated kang. The burning rate did not influence the size distribution pattern of either the heated kang or the advanced stove. Results from a radiative model show that biomass burning is an important factor for light absorptivity, and the use of an advanced stove can reduce the simple forcing efficiency value by nearly 20% in UV bands compared to the heated kang. Our results indicate that changing the combustion style from maize straw smoldering to briquette burning in an advanced stove can effectively reduce BrC emissions during heating seasons in rural areas of Guanzhong Plain.

Chemical source profiles of urban fugitive dust PM2.5 samples from 21 cities across China

Urban fugitive (road and construction) dust PM2.5 samples were collected in 21 cities of seven regions in China. Seven water-soluble ions, eight sub-fractions of carbonaceous components, and 19 elements were determined to investigate the chemical profiles of urban fugitive dust. Among the analyzed chemical compositions and on regional average, the elemental compositions showed the highest proportion (12.5-28.9% in road dust (RD) and 13.1-38.0% in construction dust (CD)), followed by water-soluble ions (5.1-19.0% in RD and 4.2-16.4% in CD) and carbonaceous fractions (5.4-9.6% in RD and 4.9-9.3% in CD). Chemical compositions measured in CD were all slightly lower than those in RD although statistically insignificant (pu202f>u202f0.05). Soil dust, which was estimated from Fe concentration, was proved to be the biggest contributor to urban fugitive dust PM2.5 mass. While, it showed a higher contribution in Northern China (71.5%) than in Southern China (52.1%). Higher enrichment factors were found for elemental S, Zn and Pb in RD than CD, reflecting stronger anthropogenic sources (i.e. vehicle exhaust) in RD. Low NO3-/SO42- and high SO42-/K+ ratios both indicated that fugitive dust was strongly influenced by stationary sources (e.g. coal combustion), and this influence was especially strong in Northern China. Coefficients of divergence proved that dust profiles within the same region were more similar than across regions, reflecting that urban fugitive dust was influenced more by local sources than long-range transport.

Characteristics and source apportionment of winter black carbon aerosols in two Chinese megacities of Xi’an and Hong Kong

Black carbon (BC) aerosols were observed over Xi’an (XA) and Hong Kong (HK) to better compare its properties and sources in two geographically separate regions in China. High-BC (7.9u2009±u20093.3xa0μg·m−3) and -PM2.5 (182u2009±u200980.5xa0μg·m−3) concentrations were observed in XA, and these were much higher than those in HK (BC, 3.2u2009±u20090.9xa0μg·m−3; PM2.5, 34.5u2009±u20099.3xa0μg·m−3). The contribution of BC to PM2.5 in HK reached 10.7%, which was ~u20091.5 times than that in XA (7.6%). The results emphasized that BC played an important role in HK PM2.5. The diurnal distribution of HK BC was highly correlated with vehicle emissions during the daytime; it peaked during heavy traffic times. Whereas XA BC exhibited flat distribution owing to stable BC sources. It is not markedly driven by traffic patterns. Additionally, the potential source contribution function (PSCF) analysis showed that XA BC mainly originated from local emissions while nearly half of the HK BC originated from distant sources, such as industrial emissions from northeastern regions and ship emissions from marine regions. These anthropogenic BC sources were found to be regional in nature based on multilinear engine (ME-2) analysis. Specifically, the XA BC sources were dominated by three factors: 22.5% from coal burning, 19.6% from biomass burning, and 32.9% from vehicle emissions. In HK, the majority of BC contributions originated from vehicle and ship emissions (78.9%), while only 14.5% and 1.5% originated from coal and biomass burning from residential combustion, as well as industrial and power plants in inland China.

Characterization and cytotoxicity of PAHs in PM 2.5 emitted from residential solid fuel burning in the Guanzhong Plain, China

The emission factors (EFs) of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 were measured from commonly used stoves and fuels in the rural Guanzhong Plain, China. The toxicity of the PM2.5 also was measured using inxa0vitro cellular tests. EFs of PAHs varied from 0.18u202fmgu202fkg-1 (maize straw charcoal burning in a clean stove) to 83.3u202fmgu202fkg-1 (maize straw burning in Heated Kang). The two largest influencing factors on PAH EFs were air supply and volatile matter proportion in fuel. Improvements in these two factors could decrease not only EFs of PAHs but also the proportion of 3-ring to 5-ring PAHs. Exposure to PM2.5 extracts caused a concentration-dependent decline in cell viability but an increase in reactive oxygen species (ROS), tumor necrosis factor a (TNF-α) and interleukin 6 (IL-6). PM2.5 emitted from maize burning in Heated Kang showed the highest cytotoxicity, and EFs of ROS and inflammatory factors were the highest as well. In comparison, maize straw charcoal burning in a clean stove showed the lowest cytotoxicity, which indicated a clean stove and fuel treatment were both efficient methods for reducing cytotoxicity of primary PM2.5. The production of these bioreactive factors were highly correlated with 3-ring and 4-ring PAHs. Specifically, pyrene, anthracene and benzo(a)anthracene had the highest correlations with ROS production (Ru202f=u202f0.85, 0.81 and 0.80, respectively). This study shows that all tested stoves emitted PM2.5 that was cytotoxic to human cells; thus, there may be no safe levels of exposure to PM2.5 emissions from cooking and heating stoves using solid fuels. The study may also provide a new approach for evaluating the cytotoxicity of primary emitted PM2.5 from solid fuel burning as well as other PM2.5 sources.