State Key Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University , Beijing 100871, China.
Wadsworth Center, New York State Department of Health , Albany, New York 12201, United States.
Environ Sci Technol. 2017 Jun 20;51(12):6849-6856. doi: 10.1021/acs.est.7b00387. Epub 2017 May 30.
Photolysis of nitric acid on the surface has been found recently to be greatly enhanced from that in the gas phase. Yet, photolysis of particulate nitrate (pNO) associated with atmospheric aerosols is still relatively unknown. Here, aerosol filter samples were collected both near the ground surface and throughout the troposphere on board the NSF/NACR C-130 aircraft. The photolysis rate constants of pNO were determined from these samples by directly monitoring the production rates of nitrous acid (HONO) and nitrogen dioxide (NO) under UV light (>290 nm) irradiation. Scaled to the tropical noontime condition on the ground level (solar zenith angle = 0°), the normalized photolysis rate constants (j) are in the range from 6.2 × 10 s to 5.0 × 10 s with a median of 8.3 × 10 s and a mean (±1 SD) of (1.3 ± 1.2) × 10 s. Chemical compositions, specifically nitrate loading and organic matter, affect the rate of photolysis. Extrapolated to ambient pNO loading conditions, e.g. ≤ 10 nmol m, the mean j value is over 1.8 × 10 s in the suburban, rural, and remote environments. Photolysis of particulate nitrate is thus a source of HONO and NO in the troposphere.
最近发现，硝酸在表面的光解作用比在气相中的光解作用大大增强。然而，与大气气溶胶相关的颗粒态硝酸盐（pNO）的光解作用仍然相对未知。在这里，使用 NSF/NACR C-130 飞机在地面附近和整个对流层收集了气溶胶滤膜样本。通过在紫外线（>290nm）照射下直接监测亚硝酸（HONO）和二氧化氮（NO）的生成速率，从这些样本中确定了 pNO 的光解速率常数。在地面正午条件下（太阳天顶角=0°）进行归一化后，归一化光解速率常数（j）的范围为 6.2×10 s 至 5.0×10 s，中位数为 8.3×10 s，平均值（±1 SD）为（1.3±1.2）×10 s。化学成分，特别是硝酸盐负荷和有机物，会影响光解速率。在环境 pNO 负荷条件下（例如，≤10nmol m）进行外推，在郊区、农村和偏远地区，平均 j 值超过 1.8×10 s。因此，颗粒态硝酸盐的光解作用是对流层中 HONO 和 NO 的一个来源。
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