What can we learn about urban air quality with regard to the first outbreak of the COVID-19 pandemic? A case study from central Europe

Abstract

Abstract. Motor vehicle road traffic in central Budapest was reduced by approximately 50 % of its ordinary level for several weeks as a consequence of various limitation measures introduced to mitigate the first outbreak of the COVID-19 pandemic in 2020. The situation was utilised to assess the real potentials of urban traffic on air quality. Concentrations of NO, NO2, CO, O3, SO2 and particulate matter (PM) mass, which are ordinarily monitored in cities for air quality considerations, aerosol particle number size distributions, which are not rarely measured continuously on longer runs for research purposes, and meteorological properties usually available were collected and jointly evaluated in different pandemic phases. The largest changes occurred over the severest limitations (partial lockdown in the Restriction phase from 28 March to 17 May 2020). Concentrations of NO, NO2, CO, total particle number (N6–1000) and particles with a diameter < 100 nm declined by 68 %, 46 %, 27 %, 24 % and 28 %, respectively, in 2020 with respect to the average reference year comprising 2017–2019. Their quantification was based on both relative difference and standardised anomaly. The change rates expressed as relative concentration difference due to relative reduction in traffic intensity for NO, NO2, N6–1000 and CO were 0.63, 0.57, 0.40 and 0.22 (%/%), respectively. Of the pollutants which reacted in a sensitive manner to the change in vehicle circulation, it is the NO2 that shows the most frequent exceedance of the health limits. Intentional tranquillising of the vehicle flow has considerable potential for improving the air quality. At the same time, the concentration levels of PM10 mass, which is the most critical pollutant in many European cities including Budapest, did not seem to be largely affected by vehicles. Concentrations of O3 concurrently showed an increasing tendency with lower traffic, which was explained by its complex reaction mechanism. Modelling calculations indicated that spatial gradients of NO and NO2 within the city became further enhanced by reduced vehicle flow.

Cloud droplet activation in a continental Central European urban environment

“…the previous paragraph). All this is in accordance with the conclusions of our more extensive study dedicated to this issue (Salma et al, 2020b).…”

“…The dependency also pointed to the size-dependent chemical composition, which is typical for urban particles. All this is in line with the ideas on the major source types such as vehicle emissions, biomass burning or new particle formation and diameter growth (NPF) events (Salma et al, 2014(Salma et al, , 2017(Salma et al, , 2020a(Salma et al, , 2020b and the particle number size distributions in Budapest (Salma et al, 2011). Photochemical processing may also play a role through chemical ageing (Furutani et al, 2008).…”

“…The CCNc was out of operation in January 2020. The overall interval also involved the emergency phase (from 12 to 27 March 2020, 16 d) and the restriction on movement phase (from 28 March to the end of the measurement year, effectively 18 d) of the first outbreak of the COVID-19 pandemic in Hungary (Salma et al, 2020b). The clocks of all measuring systems were synchronised through the computer network with an agreement of ±1 s. Local time (LT=UTC+1 or daylight-saving time, UTC+2) was chosen as the time base of the data because it was observed that the daily activity time pattern of inhabitants largely influences many atmospheric processes in cities (Salma et al, 2014;Mikkonen et al, 2020).…”

“…Thus, it can be regarded as an urban background site. The local sources comprise residential and household emissions including seasonal heating, exhaust of vehicle traffic and some industrial sources (Salma et al, 2017(Salma et al, , 2020a(Salma et al, , 2020b. Long-range transport of air masses can also play a role in shorter time intervals.…”

Effects of COVID-Induced Mobility Restrictions and Weather Conditions on Air Quality in Hungary

“…Meanwhile, a general increase in ozone levels has also become evident, attributable to the "weekend effect", or, in this case, the more pronounced "lockdown effect" of NO x -O 3 chemistry [4,5]. After the first wave of the pandemic, air pollution reduction has been reported from numerous locations worldwide [6][7][8][9][10][11], and air quality was soon identified as a mediating factor between mobility reduction and COVID cases [12][13][14]. However, systematic investigation of global measurements revealed that the air quality improvement was not necessarily observable for every location in their respective lockdown period, and, notably, the Central-Eastern European region suffered a major increase in PM 2.5 concentrations during the lockdown [8].…”