RESUMO
Despite significant improvements in air quality during and after COVID-19 restrictions, haze continued to occur in Zhengzhou afterwards. This paper compares ionic compositions and sources of PM2.5 before (2019), during (2020), and after (2021) the restrictions to explore the reasons for the haze. The average concentration of PM2.5 decreased by 28.5% in 2020 and 27.9% in 2021, respectively, from 102.49 µg m-3 in 2019. The concentration of secondary inorganic aerosols (SIAs) was 51.87 µg m-3 in 2019, which decreased by 3.1% in 2020 and 12.8% in 2021. In contrast, the contributions of SIAs to PM2.5 increased from 50.61% (2019) to 68.6% (2020) and 61.2% (2021). SIAs contributed significantly to PM2.5 levels in 2020-2021. Despite a 22~62% decline in NOx levels in 2020-2021, the increased O3 caused a similar NO3- concentration (20.69~23.00 µg m-3) in 2020-2021 to that (22.93 µg m-3) in 2019, hindering PM2.5 reduction in Zhengzhou. Six PM2.5 sources, including secondary inorganic aerosols, industrial emissions, coal combustion, biomass burning, soil dust, and traffic emissions, were identified by the positive matrix factorization model in 2019-2021. Compared to 2019, the reduction in PM2.5 from the secondary aerosol source in 2020 and 2021 was small, and the contribution of secondary aerosol to PM2.5 increased by 13.32% in 2020 and 12.94% in 2021. In comparison, the primary emissions, including biomass burning, traffic, and dust, were reduced by 29.71% in 2020 and 27.7% in 2021. The results indicated that the secondary production did not significantly contribute to the PM2.5 decrease during and after the COVID-19 restrictions. Therefore, it is essential to understand the formation of secondary aerosols under high O3 and low precursor gases to mitigate air pollution in the future.
RESUMO
Groundwater has resource, ecology, economy and society attributes. In recent years, ecological degradation caused by intensive groundwater exploitation to support socio-economic development has been of growing concern in arid and semiarid regions. To protect the groundwater sustained ecosystem, this paper developed a novel environmental risk-based hydroeconomic model to evaluate the tradeoff between groundwater utilization and ecological environmental protection in Golmud river catchment of Qaidam basin, a typical inland river watershed and alluvial aquifer, in northwestern China. Field survey, remote sensing and groundwater level monitor were conducted to obtain the threshold of groundwater dependent ecosystem. Results show that depth to groundwater table should be larger than 25.5 m in alluvial plain to prevent downstream Golmud city urban waterlogging, depth to groundwater table should be smaller than 10 m in groundwater overflow zone and fine soil plain to sustain groundwater dependent vegetation survive, and groundwater recharge to the terminal lake should be larger than 282.0 hm3 yr-1 to maintain the minimum water surface area. Meanwhile, ecosystem services value was established according to equivalent value factors per unit area provided by different types of ecosystem in Golmud river catchment. Numerical simulations model was applied to evaluate the potential environment risk, cost and benefit of ecosystem services under different groundwater demand. The investigation results show that groundwater exploitation in 2030 with 240.9 hm3 yr-1 will cause environment risk, which is terminal lake surface area smaller than permitted minimum threshold. And the recommended maximum amount of groundwater exploitation is 219.0 hm3 yr-1. This study provides guidance for regional groundwater management to maintain environment protection and socio-economy development, especially in arid regions.