岭南亚热带森林冠层大气挥发性有机物污染特征及区域人为源的影响

Pollution characteristics of volatile organic compounds above subtropical forest canopy in Lingnan and the influence of regional anthropogenic emissions

大气中挥发性有机物(VOC)对空气质量、气候变化和人体健康均有重要影响。我国南方亚热带森林地区大气VOC浓度易受区域人为源排放影响。为定量探究其影响,于2019年8—9月在鼎湖山和车八岭自然保护区森林站点,通过无人机机载设备采集并分析了午后和晚上林冠层上方不同垂直高度的大气VOC和臭氧浓度,结合WRF-GC模型模拟和情景分析定量评价了区域人为源排放对林区大气环境的影响。结果表明:林区大气植物源VOC(BVOC)浓度低,人为源VOC(AVOC)浓度相对较高;车八岭AVOC浓度低于鼎湖山,BVOC浓度则高于鼎湖山,受区域人为源排放的影响较鼎湖山小;[甲基丙烯醛(MACR)+甲基乙烯基酮(MVK)]/异戊二烯比值高,说明2个站点BVOC大气转化均较快;2个站点不同采样高度上AVOC物种浓度差异均不显著,车八岭BVOC物种浓度差异也不显著,但鼎湖山异戊二烯和α-蒎烯在25和100 m处浓度差别较大,垂直湍流扩散可解释这一差异。此外,WRF-GC模型对鼎湖山林区大气污染物地表浓度的模拟效果较好。在关闭区域人为源情景下,鼎湖山异戊二烯日均模拟浓度增加4倍,臭氧浓度降低3倍,说明我国南部亚热带森林大气受区域人为源排放影响,BVOC向其氧化产物的转化加快,可能促进植物源二次有机气溶胶(SOA)的生成,而臭氧浓度超过植物耐受阈值,长期暴露会引起林区植被损伤。

Volatile organic compounds(VOC)in the atmosphere have significant impacts on air quality,climate change,and human health.Atmospheric VOC concentrations in subtropical forests of southern China are affected by regional anthropogenic source emissions.To quantitatively explore the impacts of regional anthropogenic source emissions on forest atmosphere,VOC and ozone concentrations at different vertical levels above the canopy were collected by drone-based samplers in the afternoon and evening in Dinghushan(DHS)and Chebaling(CBL)Nature Reserves in August and September 2019 and were analyzed offline.Moreover,WRF-GC model simulations and scenario analysis were conducted to quantitatively evaluate the impact of regional anthropogenic source emissions on the atmosphere in forest areas.The results showed that the biogenic VOC(BVOC)concentrations were low and anthropogenic VOC(AVOC)concentrations were relatively high at both sites.Compared with DHS,the AVOC concentrations in CBL were lower and the BVOC concentrations were higher,which could be attributed to less anthropogenic influence by regional transport.The ratios of(MVK+MACR)/isoprene at both sites were high,indicating a rapid atmospheric conversion.No significant difference in AVOC concentrations at different sampling heights were found at both sites.BVOC concentrations in CBL were also similar for both of the sampling heights.In DHS,the concentrations of isoprene andα-pinene were significantly different for 25 and 100 m sampling heights,which may be explained by vertical eddy diffusion.Moreover,the surface concentrations of air pollutants in DHS were well simulated by WRF-GC model.Under the scenario of no anthropogenic emissions,the simulated daily average concentrations of isoprene increased by 4 times and that of ozone decreased by 3 times in DHS compared with the default setting.This result suggested that because of the influence of anthropogenic emissions in southern China,the conversion of BVOC to its oxidation products was accelerated to promote the formation of biogenic secondary organic aerosol(SOA).Meanwhile,the ozone concentrations were greater than the plant tolerance threshold,for which long-term exposure would cause vegetation damage in the forested area.