During March 2020, most European countries implemented lockdowns to restrict the transmission of SARS-CoV-2, the virus which causes COVID-19 through their populations. These restrictions had positive impacts for air quality due to a dramatic reduction of economic activity and atmospheric emissions. In this work, a machine learning approach was designed and implemented to analyze local air quality improvements during the COVID-19 lockdown in Graz, Austria. The machine learning approach was used as a robust alternative to simple, historical measurement comparisons for various individual pollutants. Concentrations of NO₂ (nitrogen dioxide), PM₁₀ (particulate matter), O₃ (ozone) and Oₓ (total oxidant) were selected from five measurement sites in Graz and were set as target variables for random forest regression models to predict their expected values during the city’s lockdown period. The true vs. expected difference is presented here as an indicator of true pollution during the lockdown. The machine learning models showed a high level of generalization for predicting the concentrations. Therefore, the approach was suitable for analyzing reductions in pollution concentrations. The analysis indicated that the city’s average concentration reductions for the lockdown period were: -36.9 to −41.6%, and −6.6 to −14.2% for NO₂ and PM₁₀, respectively. However, an increase of 11.6–33.8% for O₃ was estimated. The reduction in pollutant concentration, especially NO₂ can be explained by significant drops in traffic-flows during the lockdown period (−51.6 to −43.9%). The results presented give a real-world example of what pollutant concentration reductions can be achieved by reducing traffic-flows and other economic activities.

Microplastics are widely existed in marine and coastal environments, which aroused global concern in recent years. This review mainly summarized the interactions of organic pollutants and metals with microplastics based on environmental monitoring results and laboratory results reported by literatures. Firstly, the type, properties, and distribution of microplastics in the environment were briefly reviewed. Secondly, the property changes of microplastics after degradation were discussed. Thirdly, the concentrations of pollutants on microplastics in global environments were summarized. Then the effect of the factors (e.g. types and properties of microplastics, types of pollutants, and environmental conditions) on the sorption behaviors of microplastics were discussed in detail. Finally, the influences of microplastics on marine organisms were briefly evaluated.

The first continuous measurements of the hourly surface ozone (O3), nitric oxide (NO) and nitrogen dioxide (NO2) concentrations at 7 rural and 15 urban sites in Marmara Region of Turkey during the period from March 2013 to April 2016. The results indicate that surface O3 is an extensive problem throughout the Marmara Region. O3 levels have similar seasonal pattern in rural and urban sites by following the order of summer, spring, fall, and winter. The seasonal results showed an opposite behaviour among O3 and NOx (NO + NO2) in both rural and urban sites, marked by maximums (minimum NOx) of O3 in summer and minimums (maximum NOx) in fall and winter. The summer concentrations vary between 91.5 and 123.6 μg/m³ and 74.6–112.4 μg/m³ at rural and urban sites respectively. Furthermore, O3 peak concentration time in rural areas in O3 seasons (April–September) occurred at around 17:00–18:00 LST while in urban areas at around 15:00–16:00 LST, respectively. Air quality standards for O3 concentrations in Sile and Yalova rural sites were significantly exceeded during O3 season. This exceedance made a linkage between back trajectories and air masses with respect to the O3 levels. 72-hr back trajectories at an altitude of 500 m agl were computed by HYSPLIT model to assess the type of air masses which reach the area. AOT40 (accumulated exposure over a threshold of 40 ppb) index was performed for both vegetation and forestry standards and EU Directive were significantly exceeded at all rural stations.