[Day-Night Differences and Source Apportionment of Inorganic Components of PM2.5 During Summer-Winter in Changzhou City].

To investigate the day-night variation characteristics of inorganic components in atmospheric aerosol, PM2.5 samples were continuously collected for one month in Changzhou during summer and winter. Eleven water-soluble ions (WSⅡs) and 13 metal elements were compared in terms of their day-night character and sources. The results indicated that the day time average PM2.5 mass concentration was higher than the night time, while the percentage of the total WSⅡs in PM2.5 during the night was higher. The total WSⅡs fractions in PM2.5 were higher in winter (44%-45%) compared to summer (31%-36%), with an opposite seasonal character for metal elements (winter day 3.03%, winter night 2.29%, summer day 4.40%, summer night 4.51%). SO42-, NO3-, and NH4+, were the three main secondary ions, comprising 77%-85% of the total WSⅡs, suggesting that air pollution in Changzhou exhibits complex pollution characteristics dominated by secondary processes. The day time SO42-/WSⅡs ratio (49.0%) was slightly higher than that of the night (41.1%) due to the photochemical reaction under stronger solar radiation, while the lower NO3-(1.98 µg·m-3) in the day compared to the night (5.10 µg·m-3) was attributed to the decomposition of NH4NO3 during summer days. A good linear correlation among NH4+, SO42- and NO3-, accompanied by a ratio of predicted NH4+ to measured NH4+ near 1, illustrated that NH4+ ions mainly existed in the form of (NH4)2SO4, NH4NO3, and NH4Cl. It was concluded from the ion balance that PM2.5 was weakly alkaline in summer but neutral in winter. Fe, Al, and Zn were the largest contributors to the total metal elements, with higher concentrations of Fe and Al and lower levels of Zn in the day time. A correlation coefficient analysis and principle component analysis revealed that inorganic components come from sources that include secondary aerosol formation, suspended dust, and vehicle emissions, but there is some seasonal variation and day-night differences.

[Pollution Characteristics and Source Identification of PAHs in Atmospheric PM2.5 in Changzhou City].

A total of 55 ambient fine particle (PM2.5) samples were collected in Changzhou City from January to August 2016. The concentrations of 17 PM2.5-bound PAHs in the samples were analyzed by GC-MS. Results showed that seasonal average mass concentrations of PAHs in winter, spring, and summer were 140.24, 41.42, and 2.96 ng·m-3, respectively, which indicating that the pollution of PAHs in winter appeared more serious than in the other two seasons, and 4-6-ring high molecular weight PAHs were predominant in all three seasons. The average daily level of BaP was 3.64 ng·m-3 and the days it exceeded the permitted standard accounted for 41% of total days. PAH concentration had significant negative correlations with temperature (correlation coefficient: -0.643) and visibility (correlation coefficient: -0.466), whereas it had good positive correlations with atmospheric pressure (correlation coefficient: 0.544) and poor correlations with wind speed and relative humidity. PAH concentrations were higher at nighttime than at daytime, because of the influences of temperature difference, atmospheric stratification, as well as pollution sources. The results from the air backward trajectory model indicated that PM2.5-bound PAHs in Changzhou were mainly affected by local emission sources and short-distance transportation, whereas the contribution of long-distance transmission was small (only 11%). Based on analysis of characteristic ratios, PAHs were mainly sourced from coal burning, vehicle emissions, and biomass burning. An incremental lifetime cancer risk (ILCR) model was used to evaluate the health impact of PAHs via breathing exposure pathways. Results revealed that the ILCR of adults was higher than that of children. The ILCRs of the group for winter and spring were slightly higher than the risk threshold, but a difference was not obvious for summer.

[Characteristics and Source Identification of Carbonaceous Aerosols in PM2.5 Measurements During Summer and Fall in Changzhou].

To better understand the characterization and sources of carbonaceous components, a total of 60 fine particle (PM2.5) samples were collected in Changzhou during summer (July to August) and fall (October to November) of 2016. The average mass concentrations of PM2.5, organic carbon (OC), and elemental carbon (EC) during this study period were observed to be 73.0, 14.3 and 3.3 µg·m-3 in summer and 84.2, 13.2, and 3.5 µg·m-3 in fall, respectively. The average mass fraction of carbonaceous aerosols (OC+EC) in the PM2.5 measurement was estimated to be 24.3% in summer and 20.7% in fall. Eight carbonaceous fractions, resolved by following the IMPROVE-A thermal/optical reflectance protocol, showed strong correlation (r>0.92) between OC2, OC3, OC4 and EC1 and close correlations between EC2 and EC3 (r>0.65), indicating probable similar contributors. OC and EC were moderately correlated, suggesting complex contributions to carbonaceous aerosol. The water soluble organic carbon (WSOC) to OC ratio (WSOC/OC) in the fall (60.9%) was slightly higher than that in the summer (57.4%), while secondary organic carbon (SOC) to OC ratio (SOC/OC) was lower in the fall (49.0%) compared with the summer (52.5%). The SOC/OC ratio was lower than the WSOC/OC for both seasons, suggesting that part of WSOC component originates from primary emissions. The significant correlation of WSOC and SOC confirms that most SOC is water soluble. Relationships between each carbonaceous species and the principal component analysis indicate that vehicle emissions and coal combustion are the two main emission sources of carbonaceous aerosols from the observation period. Back trajectory analysis was used to indicate that carbonaceous components at sampling site are mainly affected by local emission sources and short distance transport, whereas the contribution of long-distance transmission is small.