[Characteristics and Generation Mechanism of Secondary Inorganic Ions in PM2.5 in Changsha-Zhuzhou-Xiangtan City Group].

Secondary inorganic ions, the main components of atmospheric PM2.5, are a dominant contributor to haze formation. The detailed characteristics and main generation mechanism of secondary inorganic ions in PM2.5 are still unclear in the Changsha-Zhuzhou-Xiangtan City Group, which is suffering from severe haze pollution, particularly in the autumn and winter seasons. For our study, we collected PM2.5 samples in November 2020 and January 2021 from four urban sites in the Changsha-Zhuzhou-Xiangtan City Group. Secondary inorganic components such as SO42-, NO3-, and NH4+ in PM2.5 were quantified. The average values(µg·m-3) of ρ(SO42-), ρ(NO3-), and ρ(NH4+) in autumn and winter were(5.2±2.5) and(7.9±4.8),(4.1±2.2) and(7.2±4.2), and(17.1±10.5) and(7.8±5.2), respectively. During the heavy haze pollution events in winter, the sum of ρ(SO42-), ρ(NO3-), and ρ(NH4+)(SNA) contributed 72.7% to the growth of PM2.5 mass concentration, and ρ(NO3-) accounted for 41.2%. This result suggested that the generation of NO3- was the key factor leading to the formation of winter haze pollution. In the polluted stage, high aerosol water content(AWC) promoted the rapid secondary generation of SNA, whereas adverse meteorological conditions also led to the accumulation of pollutants. The values of sulfur oxidation rate(SOR) and nitrogen oxidation rate(NOR) were still high in the dissipation stage. It indicated that the PM2.5 concentration fell due to the reduction in primary emissions and favorable weather conditions in dissipation, instead of the weakening of secondary generation of SNA. Compared to that in autumn, the higher AWC concentration, pH value, and lower temperature in winter were the main factors for the higher ρ(NO3-)/ρ(PM2.5) and NOR values in the Changsha-Zhuzhou-Xiangtan City Group. At the same time, the heterogeneous reaction was the main generation pathway of NO3-, when the AWC concentration was high in winter. Affected by aerosol pH value and generation rate, the liquid-phase oxidation reactions of H2O2 and SO2 were the main generation pathways of SO42- in autumn and winter in the Changsha-Zhuzhou-Xiangtan City Group. Compared to that in autumn, the higher AWC was more conducive to forming SO42-, which led to higher SOR in winter.

[Characteristics and Source Apportionment of Volatile Organic Compounds in August in the Chang-Zhu-Tan Urban Area].

Continuous sampling using the tank sampling method were conducted in Changsha, Zhuzhou, and Xiangtan cities from August 18 to 27, 2020, and 106 VOCs species were analyzed using GC-MS analysis. Then, the regional VOCs concentrations, generation potential, and source of VOCs were studied. The results showed that the average φ(VOCs) was (20.5±10.5)×10-9 in the Changsha-Zhuzhou-Xiangtan area, in which OVOCs (33.5%) and alkanes (28.2%) accounted for the highest proportion. The ozone formation potential (OFP) of VOCs was 118.5 µg·m-3, and the contributions of aromatic hydrocarbons, olefin, and OVOCs to OFP were 37.4%, 24.2%, and 23.6%, respectively. The average secondary organic aerosol formation potential (SOAp) of the VOCs was 0.5 µg·m-3, and the contribution of aromatic hydrocarbons to SOAp was 97.0%, among which C8 aromatic hydrocarbons contributed 41.7%. Toluene, m/p-xylene, and o-xylene were the common dominant species that contributed significantly to OFP and SOAp. The characteristic ratio results showed that VOCs in Changsha were relatively influenced by industrial processes and solvent use, whereas Zhuzhou and Xiangtan were more affected by coal and biomass combustion. The PMF results showed that the VOCs mainly came from vehicle exhaust and oil and gas volatilization (27.2%), coal and biomass combustion (23.7%), industrial processes (20.4%), solvent use (17.2%), and natural sources (11.5%) in the Changsha-Zhuzhou-Xiangtan area.

[Inventory and Environmental Impact of VOCs Emission from Anthropogenic Source in Chang-Zhu-Tan Region].

Based on environmental statistical data and emission factor, an anthropogenic volatile organic compounds (VOCs) emission inventory was established for the Chang-Zhu-Tan region, and a grid with spatial resolution of 3 km×3 km was built according to the spatial feature data. Ozone formation potential (OFP) and secondary organic aerosol (SOA) formation potential of anthropogenic sources were also estimated. The results showed that the total anthropogenic VOCs emission was about 113.49 kt in Chang-Zhu-Tan region and the main sources were industrial processes, solvent utilization and vehicles with the VOCs emission of 35.88 kt, 28.72 kt and 22.13 kt, respectively. Paving pitch and architecture wall painting accounted for the majority of the solvent utilization and the building materials industry accounted for 75.34% of VOCs emission from the industrial processes. Liling was the largest contributor compared to the other cities in Chang-Zhu-Tan region, where the VOCs emission from these anthropogenic sources in 2014 was 16.58 kt. The total OFP of these sources was 375.33 kt, in which solvent utilization contributed 27.28% and the O3 generative capacity of biomass burning was the largest. Solvent utilization contributed 35.35% to the total SOA formation potentials and its SOA generative capacity was also the largest. The spatial distribution characteristics revealed that the VOCs emission mostly originated from urban area.