Global inorganic nitrate production mechanisms: comparison of a global model with nitrate isotope observations
Global inorganic nitrate production mechanisms: comparison of a global model with nitrate isotope observations
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DOI：
10.5194/acp-20-3859-2020
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发表时间：
2020-03-31
影响因子：
6.3
通讯作者：
Kasibhatla, Prasad
中科院分区：
文献类型：
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作者：
Alexander, Becky;Sherwen, Tomas;Kasibhatla, Prasad
无机硝酸盐的形成是氮氧化物（NOx = NO + NO2）的主要汇。由于氮氧化物对形成对流层氧化剂（如羟基自由基（OH）和臭氧）的重要性，了解硝酸盐形成的机制和速率对于我们预测大气中大多数还原痕量气体的大气寿命的能力至关重要。硝酸盐的氧同位素组成（Delta O-17（硝酸盐））由NOx汇的相对重要性决定，因此可以为NOx化学提供观测约束。直到最近，由于我们对臭氧的氧同位素组成（Delta O-17（O-3））缺乏了解，因此无法将Delta O-17（硝酸盐）观测结果用于此目的。最近和空间上广泛的观测三角洲O-17（O-3）激励更新的比较模拟和观察三角洲O-17（硝酸盐）和重新评估模拟硝酸盐形成途径。基于最近对非均相反应的实验室研究的模型更新使五氧化二氮（N2 O 5）水解与NO2 + OH（均为41%）对地表附近（海拔1公里以下）的全球无机硝酸盐生产同样重要。所有其他硝酸盐生产机制单独代表不到6%的全球硝酸盐生产附近的表面，但可以占主导地位的地方。更新的气溶胶吸收NO2的反应速率导致显着减少的硝酸盐和亚硝酸（HONO）形成通过该途径在模型中，使NO2水解硝酸盐形成全球可忽略不计的途径。虽然气溶胶硝酸盐的光解可能对NOx、HONO和氧化剂丰度有影响，但它不会显著影响硝酸盐形成途径的相对重要性。DeltaO-17（硝酸盐）模型（千分之28.6 +/- 4.5）与全球观测汇编的平均值相当（27.6 +/- 5.0份/千份），当假设Delta O-17（O-3）= 26份/千份时，在全球范围内的氮氧化物循环和硝酸盐形成中，臭氧与HOx（= OH + HO 2 + RO 2）的相对重要性的模型表示给出了信心。
The formation of inorganic nitrate is the main sink for nitrogen oxides (NOx = NO + NO2). Due to the importance of NOx for the formation of tropospheric oxidants such as the hydroxyl radical (OH) and ozone, understanding the mechanisms and rates of nitrate formation is paramount for our ability to predict the atmospheric lifetimes of most reduced trace gases in the atmosphere. The oxygen isotopic composition of nitrate (Delta O-17(nitrate)) is determined by the relative importance of NOx sinks and thus can provide an observational constraint for NOx chemistry. Until recently, the ability to utilize Delta O-17(nitrate) observations for this purpose was hindered by our lack of knowledge about the oxygen isotopic composition of ozone (Delta O-17(O-3)). Recent and spatially widespread observations of Delta O-17(O-3) motivate an updated comparison of modeled and observed Delta O-17(nitrate) and a reassessment of modeled nitrate formation pathways. Model updates based on recent laboratory studies of heterogeneous reactions render dinitrogen pentoxide (N2O5) hydrolysis as important as NO2 + OH (both 41 %) for global inorganic nitrate production near the surface (below 1 km altitude). All other nitrate production mechanisms individually represent less than 6 % of global nitrate production near the surface but can be dominant locally. Updated reaction rates for aerosol uptake of NO2 result in significant reduction of nitrate and nitrous acid (HONO) formed through this pathway in the model and render NO2 hydrolysis a negligible pathway for nitrate formation globally. Although photolysis of aerosol nitrate may have implications for NOx, HONO, and oxidant abundances, it does not significantly impact the relative importance of nitrate formation pathways. Modeled Delta O-17(nitrate) (28.6 +/- 4.5 parts per thousand) compares well with the average of a global compilation of observations (27.6 +/- 5.0 parts per thousand) when assuming Delta O-17(O-3) = 26 parts per thousand, giving confidence in the model's representation of the relative importance of ozone versus HOx (= OH + HO2 + RO2) in NOx cycling and nitrate formation on the global scale.