The Indian megacity of Delhi suffers from some of the poorest air quality in the world. While ambient NO₂ and particulate matter (PM) concentrations have received considerable attention in the city, high ground-level ozone (O₃) concentrations are an often overlooked component of pollution. O₃ can lead to significant ecosystem damage and agricultural crop losses, and adversely affect human health. During October 2018, concentrations of speciated non-methane hydrocarbon volatile organic compounds (C₂–C₁₃), oxygenated volatile organic compounds (o-VOCs), NO, NO₂, HONO, CO, SO₂, O₃, and photolysis rates, were continuously measured at an urban site in Old Delhi. These observations were used to constrain a detailed chemical box model utilising the Master Chemical Mechanism v3.3.1. VOCs and NO_x (NO + NO₂) were varied in the model to test their impact on local O₃ production rates, P(O₃), which revealed a VOC-limited chemical regime. When only NO_x concentrations were reduced, a significant increase in P(O₃) was observed; thus, VOC co-reduction approaches must also be considered in pollution abatement strategies. Of the VOCs examined in this work, mean morning P(O₃) rates were most sensitive to monoaromatic compounds, followed by monoterpenes and alkenes, where halving their concentrations in the model led to a 15.6 %, 13.1 %, and 12.9 % reduction in P(O₃), respectively. P(O₃) was not sensitive to direct changes in aerosol surface area but was very sensitive to changes in photolysis rates, which may be influenced by future changes in PM concentrations. VOC and NO_x concentrations were divided into emission source sectors, as described by the Emissions Database for Global Atmospheric Research (EDGAR) v5.0 Global Air Pollutant Emissions and EDGAR v4.3.2_VOC_spec inventories, allowing for the impact of individual emission sources on P(O₃) to be investigated. Reducing road transport emissions only, a common strategy in air pollution abatement strategies worldwide, was found to increase P(O₃), even when the source was removed in its entirety. Effective reduction in P(O₃) was achieved by reducing road transport along with emissions from combustion for manufacturing and process emissions. Modelled P(O₃) reduced by ∼ 20 ppb h⁻¹ when these combined sources were halved. This study highlights the importance of reducing VOCs in parallel with NO_x and PM in future pollution abatement strategies in Delhi.

中文翻译：

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就地臭氧生产对印度德里的挥发性有机化合物高度敏感

印度大城市德里的空气质量是世界上最差的。虽然环境中的 NO ₂和颗粒物 (PM) 浓度在城市中受到了相当大的关注，但地面臭氧 (O ₃ ) 浓度高是污染的一个经常被忽视的组成部分。O ₃可导致严重的生态系统破坏和农作物损失，并对人类健康产生不利影响。2018 年 10 月，特定非甲烷烃类挥发性有机化合物 (C ₂ –C ₁₃ )、含氧挥发性有机化合物 (o-VOCs)、NO、NO ₂、HONO、CO、SO ₂、O _{3 的}浓度和光解率，在旧德里的一个城市地点连续测量。这些观察结果用于利用 Master Chemical Mechanism v3.3.1 约束详细的化学盒模型。VOC 和 NO _x (NO  +  NO ₂ ) 在模型中发生变化，以测试它们对局部 O ₃生产率 P (O ₃ ) 的影响，这揭示了 VOC 限制的化学体系。当仅 降低NO _x浓度时，观察到P (O ₃ )显着增加；因此，在污染减排策略中也必须考虑 VOC 共同减少方法。在这项工作中检查的 VOC 中，平均早晨P (O ₃ )率对单芳族化合物最敏感，其次是单萜和烯烃，在模型中将它们的浓度减半导致P (O ₃ )分别减少 15.6%、13.1% 和 12.9% 。P (O ₃ )对气溶胶表面积的直接变化不敏感，但对光解速率的变化非常敏感，这可能会受到 PM 浓度未来变化的影响。如全球大气研究排放数据库 (EDGAR) v5.0 全球空气污染物排放和 EDGAR v4.3.2_VOC_spec 清单所述，VOC 和 NO _x浓度被划分为排放源部门，考虑到单个排放源对P 的影响(O ₃ )进行调查。仅减少道路运输排放是世界范围内空气污染减排战略的常见策略，即使在完全去除排放源的情况下，它也会增加P (O ₃ )。P (O ₃ ) 的有效减少 是通过减少道路运输以及制造和过程排放的燃烧排放来实现的。当这些组合源减半时，模拟的P (O ₃ )减少了 约 20 ppb h ^-1。这项研究强调了在德里未来的污染减排战略中与 NO _x和 PM并行减少 VOC 的重要性。