基于铁塔观测的深圳大气VOCs垂直分布特征

2018年8～9月,利用深圳市铁塔的11个垂直梯度平台进行了9轮挥发性有机物(VOCs)不锈钢罐采样,并应用气相色谱质谱联用仪(GC/MS)对103种VOCs组分进行定量分析,研究不同垂直高度上VOCs组分特征及对近地面臭氧(O₃)生成的影响.结果表明,从地面到345m高空VOCs总体污染水平相近,在垂直梯度上变化不大;但烯烃浓度随高度上升呈现下降趋势,主要受地面天然源排放的异戊二烯主导.结合典型物种及物种对的分析发现,日间的二次生成、工业排放和光化学反应消耗是影响垂直梯度上VOCs浓度变化的主要原因.应用混合层梯度方法对VOCs通量进行计算发现,烷烃(28%)和芳香烃(23%)的通量贡献最多;二氯甲烷(1.93±0.29)mg/(m²·h)、甲苯(1.86±0.39)mg/(m²·h)具有较高的垂直通量值.结合二氧化氮(NO₂)和O₃垂直廓线的关系分析得出,总挥发性有机物(TVOCs)/NO₂在300m以上高空达到峰值,更加有利于O₃

Vertical distribution characteristics of atmospheric VOCs in Shenzhen based on tower observation

From August to September 2018, Using 11vertical gradient platforms of Shenzhen meteorological gradient observation tower, nine rounds of volatile organic compounds (VOCs) stainless steel canisters sampling were carried out, and 103kinds of VOCs were quantitatively analyzed by gas chromatography-mass spectrometry (GC/MS), to study the VOCs composition characteristics at different vertical heights and its impact on near surface ozone (O₃) formation. The results shown that the total volatile organic compounds (TVOCs) pollution level from the ground to 345m altitude was similar, and there was little change in the vertical gradient; however, the concentration of alkenes decreased with the increase of altitude, which was dominated by isoprene emitted from biogenic sources on the ground. Combined with the analysis of typical species and species pairs, it was found that the secondary formation, industrial emission and photochemical reaction consumption were the main reasons for the change of VOCs concentration on the vertical gradient. Using mixed layer gradient method to calculate VOCs flux, it was found that alkanes (28%) and aromatics (23%) contributed the most; dichloromethane (1.93±0.29) mg/(m²·h) and toluene (1.86±0.39) mg/(m²·h) had higher vertical flux. Combined with the analysis of the relationship between the vertical profiles of nitrogen dioxide (NO₂) and O₃, it was concluded that the peak value of TVOCs/NO₂ above 300m was more conducive to the O₃ formation, which was one of the important reasons for the O₃ peak value above 300m.