Variation characteristics of acid rain in Zhuzhou,Central China over the period 2011-2020

Zhuzhou was one of the most polluted cities in China with the serious acid rain.Due to the implementation of air pollution control measures from 2016 to 2018,the acid rain pollution in this city has reduced.In order to understand the recent situation,a comprehensive study on the acid rain was carried out from January 2011 to December 2020.The pH values during the study period varied from 3.3 to 7.5,with a volume-weighted mean value of 4.7.The predominant acidic components of the precipitation were SO_(4)^(2-)and NO_(3)^(-),accounting for 89.3% of the total anions.The ratio of non-sea-salt SO_(4)^(2-)to NO_(3)^(-)showed a decreasing trend,revealing that the pollution type of acid rain changed from sulfuric acid type to sulfuric acid and nitric acid compound type.The correlation analysis(p<0.05)showed that SO_(4)^(2-)was positively correlated with NH_(4)^(+),Ca^(2+),and Mg^(2+);hence,it predominated in precipitation as(NH_(4))_(2)SO_(4),NH_(4)HSO_(4),CaSO_(4),and MgSO_(4).Significant positive correlation of Ca^(2+)with Mg^(2+)shows that they may originated mainly from crust.Significant positive correlation between SO_(4)^(2-)and F^(-)and Cl^(-)indicate that their source may be related to the non-ferrous metal smelting industry in Zhuzhou.Further correlation analysis shows that emissions from the non-ferrous metal smelting industry in the area have a large significant on SO_(4)^(2-)and F^(-)in precipitation,while Cl^(-)may still be emitted from other anthropogenic sources.

Size distribution and source of heavy metals in particulate matter on the lead and zinc smelting affected area

In order to understand the size distribution and the main kind of heavy metals in particulate matter on the lead and zinc smelting affected area, particulate matter （PM） and the source samples were collected in Zhuzhou, Hunan Province from December 2011 to January 2012 and the results were discussed and interpreted. Atmospheric particles were collected with different sizes by a cascade impactor. The concentrations of heavy metals in atmospheric particles of different sizes, collected from the air and from factories, were measured using an inductively coupled plasma mass spectrometry （ICP-MS）. The results indicated that the average concentration of PM, chromium （Cr）, arsenic （As）, cadmium （Cd） and lead （Pb） in PM was 177.3 ± 33.2 μg/m^3, 37.3 ± 8.8 ng/m^3, 17.3 ± 8.1 ng/m^3, 4.8 ± 3.1 ng/m^3 and 141.6 ± 49.1 ng/m^3, respectively. The size distribution of PM displayed a bimodal distribution; the maximum PM size distribution was at 1.1-2.1 μm, followed by 9-10 μm. The size distribution of As, cd and Pb in PM was similar to the distribution of the PM mass, with peaks observed at the range of 1.1-2.1 μm and 9-10 μm ranges while for Cr, only a single-mode at 4.7-5.8 μm was observed. PM （64.7%, As （72.5%）, cd （72.2%） and Pb （75.8%） were associated with the fine mode below 2.1 μm, respectively, while Cr （46.6%） was associated with the coarse mode. The size distribution characteristics, enrichment factor, correlation coefficient values, source information and the analysis of source samples showed that As, Cd and Pb in PM were the typical heavy metal in lead and zinc smelting affected areas, which originated mainly from lead and zinc smelting sources.