Covid19-induced lockdown measures caused modifications in atmospheric pollutant and greenhouse gas emissions. Urban road traffic was the most impacted, with 48‒60% average reduction in Italy. This offered an unprecedented opportunity to assess how a prolonged (∼2 months) and remarkable abatement of traffic emissions impacted on urban air quality. Six out of the eight most populated cities in Italy with different climatic conditions were analysed: Milan, Bologna, Florence, Rome, Naples, and Palermo. The selected scenario (24/02/2020‒30/04/2020) was compared to a meteorologically comparable scenario in 2019 (25/02/2019–02/05/2019). NO₂, O₃, PM_2.5 and PM₁₀ observations from 58 air quality and meteorological stations were used, while traffic mobility was derived from municipality-scale big data.

NO₂ levels remarkably dropped over all urban areas (from ‒24.9% in Milan to ‒59.1% in Naples), to an extent roughly proportional but lower than traffic reduction. Conversely, O₃ concentrations remained unchanged or even increased (up to 13.7% in Palermo and 14.7% in Rome), likely because of the reduced O₃ titration triggered by lower NO emissions from vehicles, and lower NO_x emissions over typical VOCs-limited environments such as urban areas, not compensated by comparable VOCs emissions reductions. PM₁₀ exhibited reductions up to 31.5% (Palermo) and increases up to 7.3% (Naples), while PM_2.5 showed reductions of ∼13–17% counterbalanced by increases up to ∼9%. Higher household heating usage (+16–19% in March), also driven by colder weather conditions than 2019 (‒0.2 to ‒0.8 °C) may partly explain primary PM emissions increase, while an increase in agriculture activities may account for the NH₃ emissions increase leading to secondary aerosol formation. This study confirmed the complex nature of atmospheric pollution even when a major emission source is clearly isolated and controlled, and the need for consistent decarbonisation efforts across all emission sectors to really improve air quality and public health.

Main finding A 2-month urban traffic ban extended to the whole Italy only significantly reduced NO₂ levels, while O₃, PM_2.5 and PM₁₀ concentrations were affected to a minor extent.

Covid19 引发的封锁措施导致大气污染物和温室气体排放发生变化。城市道路交通受到的影响最大，意大利平均减少了 48-60%。这为评估长期（约 2 个月）和显着减少交通排放如何影响城市空气质量提供了前所未有的机会。分析了意大利八个气候条件不同的人口最多的城市中的六个：米兰、博洛尼亚、佛罗伦萨、罗马、那不勒斯和巴勒莫。将所选情景（24/02/2020-30/04/2020）与 2019 年的气象可比情景（25/02/2019–02/05/2019）进行了比较。NO ₂、O ₃、PM _2.5和 PM ₁₀使用了来自 58 个空气质量和气象站的观测数据，而交通流动性则来自市级大数据。

NO ₂水平在所有城市地区都显着下降（从米兰的 ‒24.9% 到那不勒斯的 ‒59.1%），下降幅度大致成正比，但低于交通减少量。相反，O ₃浓度保持不变甚至增加（在巴勒莫高达 13.7%，在罗马高达 14.7%），这可能是因为车辆的 NO 排放量较低以及 NO _x排放量低于典型的 VOC 限制导致的 O ₃滴定减少城市地区等环境，未通过可比的 VOC 排放量减少进行补偿。PM ₁₀减少了 31.5%（巴勒莫），增加了 7.3%（那不勒斯），而 PM _2.5显示减少了~13-17%，增加了~9%。较高的家庭供暖使用量（3 月增加 16-19%），也是由于比 2019 年更冷的天气条件（-0.2 至 ‒0.8 °C），可能部分解释了初级 PM 排放量的增加，而农业活动的增加可能是 NH 的原因₃排放增加导致二次气溶胶形成。这项研究证实了大气污染的复杂性，即使主要排放源被明确隔离和控制，也需要在所有排放部门进行持续的脱碳努力，以真正改善空气质量和公众健康。

主要发现 为期 2 个月的城市交通禁令扩展到整个意大利，仅显着降低了 NO ₂水平，而 O ₃、PM _2.5和 PM ₁₀浓度受到轻微影响。