Air quality simulations of PM10 and NO2 for Zagreb using ADMS-Urban dispersion modeling system

This study aims to improve the knowledge of air quality in Zagreb, the capital of Croatia. It gives insight into the spatial distribution of concentrations of the main city pollutants (fraction of particulate matter < 10 µm and nitrogen dioxide) within the process of developing an air quality modeling system in high resolution. The work is a part of an ongoing AIRQ project (AIRQ - Expansion and Modernisation of the National Network for Continuous Air Quality Monitoring) funded by the European Regional Development Fund and Environmental Protection and Energy Efficiency Fund (FZOEU).

Air pollution is perceived as the second biggest environmental concern for Europeans, next to climate change, as quoted by European Commission in 2017., and it is the most important environmental risk to human health. Over the last three decades, policies to reduce air pollution have led to improved air quality, nevertheless, in some European cities, air pollution still poses risks to health. Zagreb is, unfortunately, one of them. Based on the levels of fine particulate matter measured in the air in 2019. and 2020., among 323 European cities, Zagreb is ranked 256th, and air quality in the city is categorized as „poor“ (EEA, 2022.).

In cities, pollutant concentrations have strong gradients, in particular those related to traffic. Since continuous air quality measurements are usually representative of several square kilometers for urban background locations or representative of a specific street, authorities are encouraged to use dispersion models to complement the observations for a city.

In this study, the ADMS-Urban model was set up for the Zagreb agglomeration. Within the model, measurement data from the Desinic site were used as background data representing the contribution of long-range transport to the city. Gridded emissions (500 m by 500 m resolution) were obtained from the Croatian National Emission Inventory (source: Ministry of Economy and Sustainable Development). Since emission sectors with low emission heights, such as traffic and household emissions, generally make larger contributions to surface concentrations and health impacts in urban areas than emissions from high stacks, special attention was given to road emissions, their spatial distribution, and time profiles taking into consideration the limitation of available data.  Thus, road emissions and two large point sources were modeled explicitly. The meteorology data used within the model were from the Maksimir measurement site and are representative of the whole modeling domain.

                The focus of the analysis was the main pollutants usually found to exceed EU limit values within the city and the surrounding area PM₁₀ and NO₂. The model's performance is assessed against measurements from 14 urban, urban-background, and near-traffic sites using a range of metrics concerning annual averages, high hourly average concentrations, and diurnal cycles. The model shows good performance compared to measurements for PM₁₀, although it underestimates concentration values during high-pollution winter episodes. First NO₂ results show characteristic high concentrations at the traffic hot spots and next to the main roads.