Air quality is the biggest threat in many urban cities globally. This study measured and analyzed aerosol number size distribution between 10 to 1090 nm in the megacity Delhi during 2022. The study examined the particle number concentration in the ultrafine (<100 nm) and accumulation (100–1000 nm) ranges during day and night in terms of source's intensity, emission patterns and local meteorological conditions. Nucleation mode particles (N, 10–30 nm) contributed ∼50 % during daytime in summer periods due to increased fresh traffic emissions. In the daytime, particle concentration was dominated by smaller sizes, such as N and Aitken mode particles (N, 30–100 nm), while in the nighttime, the particles were found in Aitken and Accumulation (N, 100–1000 nm) modes. N and N were reduced by ∼45 % and 4 % at night, while N increased by ∼34 %. The mean normalized aerosol number size distribution confirmed these findings, showing clearly that N dominated during the daytime, especially during peak rush hours, and during the night particles concentration was increased up to the sizes of 300 nm particles. The aerosol number size distribution and the changes experienced in the percentage of the concentration of the different particle size ranges highlight the role of engine exhaust emissions in the atmospheric aerosol population in urban areas. The findings of the study help to identify the different source's intensity and behavior during day and nighttime, which can be used for policy formulation and decision-making to mitigate air quality and its associated health impacts.

中文翻译：

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分析昼夜道路交通变化对特大城市德里城区超细颗粒物数量分布和浓度的影响

空气质量是全球许多城市面临的最大威胁。本研究测量并分析了 2022 年大城市德里 10 至 1090 nm 之间的气溶胶数量尺寸分布。该研究检查了 2022 年白天和夜间超细（<100 nm）和累积（100-1000 nm）范围内的颗粒数量浓度。源强度、排放模式和当地气象条件。由于新交通排放的增加，夏季白天成核模式粒子（N，10-30 nm）占约 50%。白天，颗粒物浓度以较小尺寸为主，例如 N 模式和艾特肯模式颗粒（N，30–100 nm），而在夜间，颗粒物以艾特肯模式和累积模式（N，100–1000 nm）存在。 。夜间 N 和 N 分别减少约 45% 和 4%，而 N 增加约 34%。平均标准化气溶胶数量尺寸分布证实了这些发现，清楚地表明白天，尤其是高峰时段，N 占主导地位，而夜间颗粒浓度增加至 300 nm 颗粒尺寸。气溶胶数量尺寸分布和不同颗粒尺寸范围的浓度百分比的变化突出了发动机废气排放在城市地区大气气溶胶总数中的作用。研究结果有助于确定白天和夜间不同来源的强度和行为，可用于政策制定和决策，以减轻空气质量及其相关的健康影响。