# Impact of COVID-19 Mobility Changes on Air Quality in Warsaw
### Changes in Mobility and Air Quality under COVID-19 Conditions  
The COVID-19 pandemic brought a huge change in the lifestyle of societies. For example, confinement at home, remote working and remote education are caused by \"stay-at-home orders\" and the shutdown of public facilities. This has caused major changes in transportation behaviour and associated environmental impacts. These issues have been analysed in numerous countries. Studies relating to the first wave of the pandemic (spring 2020) showed that the total mobility of the population decreased significantly during lockdowns, which were introduced in most European countries, which resulted in the closure of schools, universities, theatres, cinemas, restaurants and other service establishments and the transition of a large part of the population to working from home. In many countries, it was even forbidden to leave home, except in essential situations. The decrease in the number of trips observed in individual countries and European cities was at a similar level. In Rome and the Spanish city of Santander, it was 77% and 76%, respectively [16]. Swiss analysis shows that the overall number of trips in the country fell by around 60% [17]. In Sweden, on the basis of mobile phone travel data, it was found that the number of trips made on weekdays decreased by about 40% [18]. A similar decline has been reported in Germany [19]. Changes in mobility were measured in different ways. Data from intelligent transport systems (ITS) devices such as induction loops, surveillance cameras, metro gates, urban public bicycle systems, and public transport occupancy surveys were used [16; 17; 18]. Mobile phone movement data have become an important source of information [16; 18]. In Poland, surveys have been carried out to determine the extent to which the pandemic has affected mobility [20]. Public transport in Gdansk was analysed in detail [21]. Changes in mobility have affected different transport sectors to varying degrees. With regard to car traffic, the impact was lower than for public transport. Car transport was returning much more quickly to the state seen before the lockdown. In the case of Switzerland, two months after the end of the biggest restrictions, private transport use returned to its 2019 level, while public transport remained at 50% [17]. In Rome, during the lockdown phase, the number of trips made by cars decreased by 40% and by trucks by 25%. In Germany, the proportion of people using cars (but not exclusively) has halved. However, there was an increase in car use from 53% to 66% among those who used only this mode of transport [22]. The pandemic has also influenced preferences regarding the choice of mode of transport. As public transport became less popular, the proportion of private transport users sometimes increased. In Santander, Spain, the share of trips made by private cars increased from 48.33% to 76.84%, with a decrease in public transport trips from 41.65% to 19.14% [16]. In Budapest, the share of people using public and private transport before the pandemic was at the same level (about 43%). After the restrictions were introduced, public transport users accounted for only 18% and car users 65% [23]. Due to the observed decrease in mobility, many regions have reported lower levels of air pollution, particularly in terms of NO\({}_{2}\) concentrations [24; 25; 26]. Based on data from NASA (National Aeronautics and Space Administration, Washington, DC, USA) and ESA (European Space Agency, Paris, France), it was found that in places most struggling with the SARS-CoV-2 virus, such as Wuhan and cities in Italy, Spain and the USA, NO\({}_{2}\) concentrations dropped by up to 30% [27]. Studies carried out in Puglia, Italy, in March and April 2020 showed significant differences in NO\({}_{2}\) concentrations in the air compared to the previous year. In Bari, the average concentration of NO\({}_{2}\) in the air was 48.2 \(\upmu\)g/m\({}^{3}\) during the lockdown, while one year before it was at 62.2 \(\upmu\)g/m\({}^{3}\), a decrease of more than 20%.