# Impact of COVID-19 Mobility Changes on Air Quality in Warsaw
## 5 Conclusions  
In the IDUB project, a unique analysis was performed of the impact of the COVID-19 pandemic on the volume of traffic generated in Warsaw during the first months of lockdown, in the period March-June 2020. The data obtained were compared with data on nitrogen dioxide concentrations collected at the air quality monitoring station located in the immediate vicinity of the road and data on concentrations of PM2.5 and PM10 at a station located in a residential district of Warsaw with a predominant share of single-family housing. The completed project confirmed the legitimacy and feasibility of effective use of big data (SIM card movements provided by mobile phone operators) in analysing the mobility of people and reconstructing behaviour (post factum) in very unusual situations (e.g., major changes in mobility due to restrictions imposed during the pandemic), with the possibility of comparing operating states of transport systems in pre- and post-event situations, was confirmed. This is a valuable conclusion from the work because, in the future, we should expect other situations in which it will not be possible to perform traditional, comprehensive traffic studies. The analyses of individual mobility clearly confirmed the expectations regarding the effects of the restrictions introduced in subsequent phases of the pandemic. Thanks to the research work, significantly lower mobility of the population were observed in the following months of the lockdown compared to previous years. These values was quantified. Similarly, as a result of the project, data on the reduction in NO\({}_{2}\) concentrations resulting from changes in mobility were presented and compared to previous years. The March-April 2020 period saw a decrease of approximately 35-40% from the 2017 to 2019 averages. A comparison of mobility data acquired from big data with data on concentrations of nitrogen dioxide, PM2.5 and PM10 revealed an interesting relationship between the increase in the number of trips generated and NO\({}_{2}\) concentrations. A 25% increase in the average hourly (calculated on a daily basis) number of trips generated between April and May corresponded to a 25% increase in NO\({}_{2}\) concentrations. Additionally, an even greater impact was recorded during the afternoon traffic peak period. With an increase in generated traffic of 28% (calculated on average during the peak hour in March-May), the increase in NO\({}_{2}\) concentrations was 51%. As a part of the research work, an interesting effect related to the reduction in mobility at the beginning of the year was also detected. There was an increase in daily concentrations of PM2.5 and PM10 in 2020 compared to the year 2019, especially in the first months of lockdown (March-April) with reduced mobility levels compared to previous years. This is attributed to increased emissions of air pollutants from households, which were associated with the population's remaining isolated at home due to the pandemic-induced restrictions being implemented. It is worth emphasising that the mobility data obtained and used in this paper is an important source of knowledge about the transport behaviours of citizens and about changes that have occurred during pandemic restrictions. The possibility of linking this data with air quality data creates additional opportunities to draw interesting conclusions that may be important from the point of view of air quality management (including emission source control), health management, and possibly also in the field of crisis management. Although in Polish conditions, such solutions do not yet function fully, it can certainly be assumed that the role of big data in issues related to air (environment) and health protection and their relationships with the variability of pressure from various emission sources (including road traffic) will increase. The pandemic effects for Warsaw determined in the study are comparable with the data obtained from the literature review. Both reduced mobility and lower levels of air pollution were confirmed.