北京城区冬春季过氧化氢浓度变化特征

大气过氧化氢（H₂O₂）是一种重要的光化学产物，也是硫酸盐气溶胶生成及降水酸化过程的关键氧化剂。然而，我国对H₂O₂的观测研究较少，尤其对雾霾期间H₂O₂浓度变化特征认识不足。该文介绍了冬春时段（2016年12月-2017年4月）在北京城区中国气象局的H₂O₂观测结果，并结合同期O₃，PAN，NO_X，PM_2.5等污染物和气象要素观测数据，分析H₂O₂浓度变化特征与影响因素。观测结果表明:观测期间H₂O₂体积混合比（简称为浓度）为（0.65±0.59）×10-9，其中，春季浓度（0.83±0.67）×10-9高于冬季浓度（0.51±0.47）×10-9；H₂O₂平均日变化基本呈现单峰特征，峰值出现在18:00-21:00，比其他地区峰值出现稍晚，并滞后于O₃峰值时间4~7 h；相对湿度对H₂O₂日峰值时间和浓度水平有影响，小于55%时日峰值出现于18:00-24:00，平均峰值浓度1.52×10-9；大于65%时日峰值出现于11:00-16:00，日峰值浓度均小于1×10-9。H₂O₂，O₃和PAN虽然同属光化学产物，但在不同污染状况下浓度水平和变化趋势差异明显；H₂O₂清洁日峰值浓度高于污染日，但11:00-15:00污染日浓度略高于清洁日。

Characteristics of Atmospheric Hydrogen Peroxide at an Urban Site in Beijing During Winter and Spring

As a photochemical produced oxidant, gaseous hydrogen peroxide (H₂O₂) plays an important role in aerosols and acid rain production. However, not many measurements of gaseous H₂O₂ have been made in China in the past few years and further studies especially the level and trend of H₂O₂ in smog are needed. To make up for the lack of H₂O₂ data and provide support for air quality improvement in China, an observation experiment on gaseous H₂O₂ is carried out from 27 Dec 2016 to 28 Apr 2017 at an urban site in the northwest of mega-city Beijing, using a two-channel H₂O₂ monitor AL2021. The concentration level, variation and influence factors under different conditions are analyzed with several simultaneously observed pollutants (O₃, PAN, NO_X, PM_2.5, etc.) and meteorological parameters. The mean mixing ratio of H₂O₂ for the entire period is (0.65±0.59)×10^-9, with a higher mean of (0.83±0.67)×10^-9 in spring and a lower mean of (0.51±0.47)×10^-9 in winter. Day peaks with the value higher than 2×10^-9 is also detected in winter indicating that high concentration of H₂O₂ can also happen under certain conditions. The concentration of H₂O₂ shows pronounced diurnal cycles with peaks in the period of 1800-2100 BT, occurring later than those reported for other sites in China or foreign countries and shows a delay of about 4 to 7 hours compared with the peaking time of O₃. H₂O₂ level is found to be negatively correlated with relative humidity (RH), especially when only considering the maximum H₂O₂ level under RH over 55%. This is consistent with the uptake of gaseous H₂O₂ by water-containing aerosol particles under higher RH conditions. The H₂O₂ peaking time and peak level are closely related with RH as well as other factors, such as NO_X. Under conditions of daily RH lower than 55%, H₂O₂ level can reach a mean peak value of 1.52×10^-9 with peaking times during 1800-2400 BT, while it peaks lower (1×10^-9) and earlier (before 1700 BT) with the daily mean RH higher than 65%. H₂O₂, O₃ and PAN show different diurnal patterns and levels under different pollution conditions. H₂O₂ shows smaller average level differences for clean and hazy days, with a higher peak but a lower level during 1100-1500 BT under the clean condition. O₃ shows a higher mixing ratio under clean condition than under hazy condition, while PAN reveals an opposite trend. Results also indicate that dynamical transport could be an important influencing factor of variations and levels of H₂O₂ and O₃. The impact of photochemistry on haze formation in colder months in the urban environment of Beijing and its feedback warrant further studies, particularly the role of H₂O₂ in the formation of sulfate aerosol.