Abstract A well-evaluated Comprehensive Air quality Model with extensions (CAMx) was used to simulate concentrations of secondary inorganic aerosols in fine particulate matter (PM2.5) over Pearl River Delta (PRD) region during two separate months (April and October) in 2013. An indicator of adjusted gas ratio (AdjGR) was used to characterize PM chemistry under both NH3-poor (NP) and NH3-rich (NR) conditions as well as to identify their respective spatiotemporal patterns at different PM2.5 levels. The results were as follows: (1) Based on both observed molar ratio of [NH4+]/[SO42−] and modeled AdjGR, NR and NP conditions exhibited diurnal, daily, and seasonal variations. (2) A larger area in PRD had NP conditions over the two months when pollution was apparent; this NP region tended to occur downwind of PRD in October and the central region of PRD in April, with high PM2.5 concentrations in both. (3) This wider NP distribution could be related to higher nitrogen oxidation ratio (NOR), with more NOx converting to nitrate. Under conditions of higher pollution, there were relative lower degree of sulfate neutralization (DSN) and particle neutralization ratio (PNR). This supports the claim that NH3 may not be fully neutralized by SO42−. (4) Modeled AdjGR displayed clear hourly variations, with the lowest levels occurring in the afternoon. Reducing NH3 emission is not as efficient as NOx at increasing evening nitrate concentrations. (5) To mitigate PM2.5 pollution even further, a greater reduction of NH3 should be suggested in chemical regions transiting to NR condition when there are lower SO2 and NOx emissions.

中文翻译：

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珠江三角洲贫氨富氨区无机气溶胶形成特征

摘要 使用经过充分评估的带扩展的综合空气质量模型 (CAMx) 来模拟珠江三角洲 (PRD) 地区在两个不同的月份（4 月和 10 月）中细颗粒物 (PM2.5) 中二次无机气溶胶的浓度。 2013. 调整气体比率 (AdjGR) 指标用于表征在贫氨 (NP) 和富氨 (NR) 条件下的 PM 化学特征，并确定它们在不同 PM2.5 水平下各自的时空模式。结果如下： (1) 基于观察到的 [NH4+]/[SO42-] 摩尔比和模拟的 AdjGR，NR 和 NP 条件表现出昼夜、每日和季节性变化。(2) 污染明显的两个月内，珠三角有较大面积出现NP条件；该NP地区10月多出现在珠三角下风向，4月多出现在珠三角中部，PM2.5浓度均偏高。(3) 这种更宽的 NP 分布可能与更高的氮氧化率 (NOR) 有关，更多的 NOx 转化为硝酸盐。在较高污染条件下，硫酸盐中和度（DSN）和颗粒中和率（PNR）相对较低。这支持了 NH3 可能不会被 SO42- 完全中和的说法。(4) Modeled AdjGR 显示出清晰的每小时变化，最低水平出现在下午。在增加夜间硝酸盐浓度方面，减少 NH3 排放不如 NOx 有效。(5) 进一步减轻 PM2.5 污染，