珠江三角洲光化学活跃期甲醛及其前体物的源解析研究

选取珠江三角洲大气超级站的三个代表性超级站点（东莞东城城市超级站、深圳莲花山城市超级站和鹤山花果山区域超级站），同步在线监测和分析了2021年5~10月大气光化学活跃期甲醛（HCHO）及其前体物挥发性有机物（VOCs）组分的时空变化特征，利用多元线性回归法对HCHO来源进行解析，识别出了关键VOCs前体物及其贡献，并对比了三个点位来源及前体物的差异.结果表明：三个站点的HCHO体积浓度存在明显差异，鹤山区域站浓度最高达5.82×10^-9，与历史研究数据相比浓度升高，而城市超级站东城与莲花山浓度水平降低.臭氧浓度与甲醛浓度存在一定相关性，各站点臭氧浓度最高的9月，HCHO的平均浓度水平也高；臭氧超标日的HCHO浓度显著高于臭氧非超标日.利用多元线性回归法，选择甲苯、异戊二烯和O₃作为源示踪剂，结果表明二次源对HCHO来源贡献占比最多，范围为43.5%~54.9%，其中区域站点二次源占比高于其它两个城市站点.基于生成产率法得到各站点二次转化生成HCHO的前体物主要为烯烃，其中贡献最大的是异戊二烯，其次为乙烯和丙烯.综合对比，HCHO的一次人为源的下降导致城市站点HCHO浓度降低，较高的二次转化导致了区域站点HCHO浓度升高，需重点关注甲醛的人为源直接排放和异戊二烯、苯乙烯、乙烯等前体物.

Research on the sources of formaldehyde and its precursors during the active period of atmospheric photochemistry in the Pearl River Delta

Based on three representative Air Quality Monitoring supersites in the Pearl River Delta (PRD) region (Dongcheng urban station in Dongguan, Lianhuashan urban station in Shenzhen and Huaguoshan rural station in Heshan), we monitored and analyzed spatial-temporal variation characteristics of formaldehyde (HCHO) and its precursor volatile organic compounds (VOCs) during the active period of atmospheric photochemistry from May to October 2021. This study analyzed the sources of HCHO by multiple linear regression, identified its key VOCs precursors and their contributions, and compared the differences in the sources and precursors of HCHO between three sites. There were obvious differences in the volumetric concentrations of HCHO among the three sites, with the highest concentration in Huaguoshan reaching 5.82×10^-9. Compared with the historical data, the HCHO concentration in the rural Huaguoshan site was elevated, while the HCHO concentrations in the urban Dongcheng and Lianhuashan sites were decreased. There was a certain correlation between O₃ and HCHO concentrations. In September, when the ozone concentration was the highest, the concentration of HCHO was also increased. In addition, the HCHO concentration on ozone exceedance days was significantly higher than those on ozone non-exceedance days. Using the multiple linear regression method, and selecting toluene, isoprene and O₃ as source tracers, it was obtained that the secondary sources contributed the most to the HCHO formation, with the proportion ranging from 43.5% to 54.9%. The proportion of secondary sources at the rural site was higher than that of the other two urban sites. Based on the production yields method, the precursors of the secondary formation of HCHO at each site are mainly olefins, of which the largest contribution was from isoprene, followed by ethylene and propylene. In comparison, it was speculated that the decrease in anthropogenic sources of HCHO led to the decrease of HCHO concentrations at urban sites, while the higher contribution of secondary sources led to an increase of HCHO concentration at the rural site. These results suggested that it was necessary to focus on the control of the anthropogenic source of HCHO and its precursors such as isoprene, styrene and ethylene.