Quantifying road traffic impact on air quality in urban areas: A Covid19-induced lockdown analysis in Italy

Abstract

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). NO 2 , O 3 , PM 2.5 and PM 10 observations from 58 air quality and meteorological stations were used, while traffic mobility was derived from municipality-scale big data. NO 2 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, O 3 concentrations remained unchanged or even increased (up to 13.7% in Palermo and 14.7% in Rome), likely because of the reduced O 3 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. PM 10 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 NH 3 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.

Nitrogen dioxide reductions from satellite and surface observations during COVID-19 mitigation in Rome (Italy)

“…The sharp decrease in NO 2 concentrations in the rural site could lead to a decrease in ozone, since atmospheric chemistry is under NO x -limited regime whereas for urban areas the opposite happened, as previously demonstrated (Sicard et al 2013;Simon et al 2015;Witte et al 2011). These results are consistent with recent findings observed in Italy and in other regions of the world (Gualtieri et al 2020;Sharma et al 2020;Sicard et al 2020;Venter et al 2020;Xu et al 2020aXu et al , 2020bZhao et al 2020).…”

“…As said before, the road transport sector is the main source of NO x emissions in Europe: in Rome, road transport corresponds to more than 50% of total NO 2 emissions, as previously shown in Table S1. Similar reductions in air pollution have been observed in Italy and in other regions of the world (Gualtieri et al 2020;Muhammad et al 2020;Nakada and Urban 2020;Sicard et al 2020;Tobías et al 2020).…”

Analysis of lockdown for CoViD-19 impact on NO2 in London, Milan and Paris: What lesson can be learnt?

“…The introduction of these measures could have caused a reduction in NO 2 from vehicular traffic already in the year 2019 and therefore less visibility of the effect of the lockdown, given the blocking of more polluting vehicles. This explanation had already been advanced also by Gualtieri et al (2020) in their analysis of air quality of several Italian cities during the lockdown for CoViD-19. In fact, several researches conducted in recent years have shown the positive effects of LEZs on the urban environment in terms of lower NO 2 concentration ( Ferreira et al, 2015 ; Holman et al, 2015 ; Jiang et al, 2017 ).…”

Positive effects of COVID-19 lockdown on air quality of industrial cities (Ankleshwar and Vapi) of Western India

“…However, different trends of some pollutants (minimal increment during later phases) are probably due to two primary causes. First, the diversity in the industrial setup and decline in the number of the on-road vehicle 3 , 56 . Ankleshwar hosts the majority of pharmaceutical manufacturing plants, while Vapi houses more heterogeneous industries, such as pharmaceutical, petrochemical, etc.…”