State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China.
State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China; International Joint Laboratory for Regional Pollution Control, Ministry of Education, Beijing 100816, China; Collaborative Innovation Centre of Atmospheric Environment and Equipment Technology, Nanjing University of Information Science & Technology, Nanjing 210044, China.
Sci Total Environ. 2021 Feb 20;756:144127. doi: 10.1016/j.scitotenv.2020.144127. Epub 2020 Nov 25.
Photolysis of nitrous acid (HONO) is one of the major sources for atmospheric hydroxyl radicals (OH), playing significant role in initiating tropospheric photochemical reactions for ozone (O) production. However, scarce field investigations were conducted to elucidate this effect. In this study, a field campaign was conducted at a suburban site in southwest China. The whole observation was classified into three periods based on O levels and data coverage: the serious O pollution period (Aug 13-18 as P1), the O pollution period (Aug 22-28 as P2) and the clean period (Sep 3-12 as P3), with average O peak values of 96 ppb, 82 ppb and 44 ppb, respectively. There was no significant difference of the levels of O precursors (VOCs and NOx) between P1 and P2, and thus the evident elevation of OH peak values in P1 was suspected to be the most possible explanation for the higher O peak values. Considering the larger contribution of HONO photolysis to HO primary production than photolysis of HCHO, O and ozonolysis of Alkenes, sensitivity tests of HONO reduction on O production rate in P1 are conducted by a 0-dimension model. Reduced HONO concentration effectively slows the O production in the morning, and such effect correlates with the calculated production rate of OH radicals from HONO photolysis. Higher HONO level supplying for OH radical initiation in the early morning might be the main reason for the higher O peak values in P1, which explained the correlation (R = 0.51) between average O value during daytime (10:00-19:00 LT) and average HONO value during early morning (00:00-05:00 LT). For nighttime accumulation, a suitable range of relative humidity that favored NO conversion within P1 was assumed to be the reason for the higher HONO concentration in the following early morning which promoted O peak values.
亚硝酸（HONO）的光解是大气羟基自由基（OH）的主要来源之一，在引发臭氧（O）产生的对流层光化学反应中起着重要作用。然而，对于这一效应的实地研究却很少。在本研究中，在中国西南部的一个郊区站点进行了实地考察。根据 O 水平和数据覆盖范围，整个观测分为三个时期：严重的 O 污染时期（8 月 13 日至 18 日为 P1）、O 污染时期（8 月 22 日至 28 日为 P2）和清洁时期（9 月 3 日至 12 日为 P3），平均 O 峰值分别为 96ppb、82ppb 和 44ppb。P1 和 P2 之间 O 前体（VOCs 和 NOx）的水平没有显著差异，因此，OH 峰值的明显升高很可能是 O 峰值升高的最可能解释。考虑到 HONO 光解对 HO 初级生成的贡献大于 HCHO 光解、烯烃的光解和臭氧化，通过零维模型对 P1 中 O 生成速率的 HONO 还原的敏感性进行了测试。减少的 HONO 浓度有效地减缓了清晨的 O 生成速度，这种影响与从 HONO 光解计算出的 OH 自由基生成率相关。清晨为 OH 自由基引发提供更高的 HONO 水平可能是 P1 中 O 峰值较高的主要原因，这解释了白天（10：00-19：00LT）平均 O 值与清晨（00：00-05：00LT）平均 HONO 值之间的相关性（R=0.51）。对于夜间积累，假设在 P1 内有利于 NO 转化的合适相对湿度范围是随后清晨更高 HONO 浓度的原因，这促进了 O 峰值的升高。
