Abstract SAPRC16 is an interim update to the SAPRC series of chemical mechanisms that includes updated rate constants, a revised representation of radical chemistry, and a new speciation lumping scheme to better develop predictions of SOA precursors. In this study, the ability of the SAPRC16 chemical mechanism to simulate regional ozone episodes is tested in seven (7) major cities across the United States. The UCD-CIT 3-dimensional (3D) airshed model was configured with both SAPRC11 (base mechanism) and SAPRC16 (updated mechanism). Concentrations of ozone, hydroxyl radical (OH) and hydroperoxyl (HO2) radical predicted with both mechanisms were compared to measured values. It was generally observed that SAPRC16 predicts slightly lower ozone concentrations than SAPRC11 in NOx rich urban centers. A box model analysis shows that the SAPRC16 mechanism quenches ozone production earlier than SAPRC11 as NOx concentrations increase (yielding decreasing VOC/NOx ratios). This could be caused by more detailed HO2+RO2 reactions and RO2 isomerization reactions in SAPRC16 that compete with the HO2+NO reaction. Predictions from SAPRC11 are in better agreement with the measurements in the western United States, however SAPRC16 outperforms SAPRC11 in some eastern and southern U.S. cities. These results may also be strongly influenced by the accuracy of emissions inventories in each region. Differences in ozone concentrations predicted by SAPRC16 and SAPRC11 increased as emissions decreased suggesting that the two mechanisms will predict different outcomes from future emissions control programs. In general, the SAPRC11 mechanisms slightly over-predicts OH concentration while under-predicting HO2 radical concentration and the SAPRC16 mechanism slightly under predicts OH and under predicts HO2, sometimes by large amounts. The reasons for this behavior are unknown at this time. These features will influence the secondary organic aerosol (SOA) predictions from each mechanism since the branching between high NOx and low NOx regimes depends on calculated HO2 concentrations. Further analysis of the HO2+RO2 reactions and RO2 isomerization reactions and the reasons for the lower HO2 predictions in the updated SAPRC16 chemical mechanism should be carried out before widespread adoption of the new mechanism.

中文翻译：

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用于环境模拟的 SAPRC16 化学机理分析

摘要 SAPRC16 是 SAPRC 系列化学机制的临时更新，包括更新的速率常数、自由基化学的修订表示和新的物种形成集总方案，以更好地预测 SOA 前体。在这项研究中，SAPRC16 化学机制模拟区域臭氧事件的能力在美国七 (7) 个主要城市进行了测试。UCD-CIT 3 维 (3D) 流域模型配置了 SAPRC11（基础机制）和 SAPRC16（更新机制）。将使用两种机制预测的臭氧、羟基自由基 (OH) 和过氧化氢 (HO2) 自由基的浓度与测量值进行比较。人们普遍观察到，在富含 NOx 的城市中心，SAPRC16 预测的臭氧浓度略低于 SAPRC11。箱式模型分析表明，随着 NOx 浓度的增加（产生降低的 VOC/NOx 比率），SAPRC16 机制比 SAPRC11 更早地抑制臭氧产生。这可能是由于 SAPRC16 中更详细的 HO2+RO2 反应和 RO2 异构化反应与 HO2+NO 反应竞争造成的。SAPRC11 的预测与美国西部的测量结果更加一致，但 SAPRC16 在美国东部和南部的一些城市的表现优于 SAPRC11。这些结果也可能受到每个地区排放清单准确性的强烈影响。SAPRC16 和 SAPRC11 预测的臭氧浓度差异随着排放量的减少而增加，这表明这两种机制将预测未来排放控制计划的不同结果。一般来说，SAPRC11 机制略微高估了 OH 浓度，而低估了 HO2 自由基浓度，而 SAPRC16 机制略微低估了 OH 和预测了 HO2，有时预测值很大。目前尚不清楚这种行为的原因。这些特征将影响来自每种机制的二次有机气溶胶 (SOA) 预测，因为高 NOx 和低 NOx 状态之间的分支取决于计算的 HO2 浓度。在广泛采用新机制之前，应进一步分析 HO2+RO2 反应和 RO2 异构化反应，以及更新 SAPRC16 化学机制中 HO2 预测值较低的原因。有时是大量的。目前尚不清楚这种行为的原因。这些特征将影响来自每种机制的二次有机气溶胶 (SOA) 预测，因为高 NOx 和低 NOx 状态之间的分支取决于计算的 HO2 浓度。在广泛采用新机制之前，应进一步分析 HO2+RO2 反应和 RO2 异构化反应，以及更新 SAPRC16 化学机制中 HO2 预测值较低的原因。有时是大量的。目前尚不清楚这种行为的原因。这些特征将影响来自每种机制的二次有机气溶胶 (SOA) 预测，因为高 NOx 和低 NOx 状态之间的分支取决于计算的 HO2 浓度。在广泛采用新机制之前，应进一步分析 HO2+RO2 反应和 RO2 异构化反应，以及更新 SAPRC16 化学机制中 HO2 预测值较低的原因。