PM2.5 from the Guanzhong Plain: Chemical composition andimplications for emission reductions

Atmospheric particulate matter (PM) affects important environmental issues including air quality, regional and global climates, and human health. A one-year sampling campaign for PM2.5 was conducted at six locations in Guanzhong Plain, including the cities of Xi&#39;an, Weinan and Baoji, from March 2012 to March 2013. The 24-h average PM2.5 mass concentration was 134.7&nbsp;&mu;g&nbsp;m&minus;3, that substantially exceeds the National Ambient Air Quality Standard level of 35&nbsp;&nbsp;&mu;g&nbsp;m&minus;3. The highest loadings of both organic and elemental carbon (OC and EC) occurred in winter: EC co-varied with OC but showed less variability, presumably due to more stable emissions. The greatest contributions of secondary inorganic ions (SO42&minus;, NO3&minus; and NH4+) to the total quantified ions also were seen in winter, presumably due to gaseous precursors from coal combustion and biomass burning. Two high PM episodes occurred, one in the autumn and the other in winter. During the autumn episode, regional pollution from biomass burning raised the concentrations of secondary ions while coal combustion was a strong influence during the winter episode. Modeling simulations suggest that the control measures on both primary emissions and secondary aerosol precursors including SO2, NOx, and NH3 are needed to reduce the PM levels of the region.</p

Characteristics and major sources of carbonaceous aerosols in PM2.5 fromSanya, 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.</p

Microscale spatial distribution and health assessment of PM2.5-boundpolycyclic aromatic hydrocarbons (PAHs) at nine communities inXi'an, China

Spatial variability of polycyclic aromatic hydrocarbons (PAHs) associated with fine particulate matter (PM2.5) was investigated in Xi&#39;an, China, in summer of 2013. Sixteen priority PAHs were quantified in 24-h integrated air samples collected simultaneously at nine urban and suburban communities. The total quantified PAHs mass concentrations ranged from 32.4 to 104.7&nbsp;ng&nbsp;m&minus;3, with an average value of 57.1&nbsp;&plusmn;&nbsp;23.0&nbsp;ng&nbsp;m&minus;3. PAHs were observed higher concentrations at suburban communities (average: 86.3&nbsp;ng&nbsp;m&minus;3) than at urban ones (average: 48.8&nbsp;ng&nbsp;m&minus;3) due to a better enforcement of the pollution control policies at the urban scale, and meanwhile the disorganized management of motor vehicles and massive building constructions in the suburbs. Elevated PAH levels were observed in the industrialized regions (west and northwest of Xi&#39;an) from Kriging interpolation analysis. Satellite-based visual interpretations of land use were also applied for the supporting the spatial distribution of PAHs among the communities. The average benzo[a]pyrene-equivalent toxicity (&Sigma;[BaP]eq) at the nine communities was 6.9&nbsp;&plusmn;&nbsp;2.2&nbsp;ng&nbsp;m&minus;3 during the sampling period, showing a generally similar spatial distribution to PAHs levels. On average, the excess inhalation lifetime cancer risk derived from &Sigma;[BaP]eq indicated that eight persons per million of community residents would develop cancer due to PM2.5-bound PAHs exposure in Xi&#39;an. The great in-city spatial variability of PAHs confirmed the importance of multiple points sampling to conduct exposure health risk assessment.</p