Evaluation of Emission Factors for Particulate Matter and NO2 from Road Transport in Sofia, Bulgaria

Traffic-related air pollution has a significant impact on the concentration of particulate matter (PM) and nitrogen oxides (NOx) in urban areas, but there are many uncertainties associated with the modeling of PM concentration due to non-exhaust emissions. Bulgarian weather, road surfaces and traffic conditions differ significantly from the UK’s and other EU countries’ averages, which underpin many assumptions in established models. The hypothesis is that the emission factors differ from those used to calculate traffic emissions using the EMIT model. The objective of this work is to adjust the emissions for PM and the relationship between the fractions of NOx and PM using the hourly mean concentrations from road transport and urban background automatic air quality stations in Sofia, Bulgaria. Various already-published and newly developed methods are applied to local observations to derive functions and relations that better represent Bulgarian road and traffic conditions. The ADMS-Urban model is validated and evaluated by comparing pollutant concentrations from simulations using original and adjusted emissions, showing an improvement in results after applying functions and relationships derived from local observations. This work is part of our efforts to improve air quality modeling in urban areas in Bulgaria.