Performance of Operational Chemical Transport Models for Particulate Matter Concentrations in Bulgaria Hristina Kirova , Nadya Neykova , and Emilia Georgieva Abstract The main objective of this study is to evaluate the performance of some well-known and widely used operational air quality modelling systems (EMEP- MSC-W, and the models at the Copernicus Atmosphere Monitoring Service (CAMS)) for simulations of ground-level particulate matter in Bulgaria. The analysis is focused on two months—a summer one (August 2017) and a winter one (February 2019). The comparison of models to observations from regular air quality background stations is based on statistical indicators and various plots (box plots, kernel density esti- mations, and scatter plots). The EMEP and CAMS regional models underestimate the observed concentrations, on average by about 50% for PM 10 and by about 22% for PM 2.5 . These models perform better at a rural remote (mountain) site than at urban background stations indicating that the outputs of the models could be used for indicative values of PM background concentrations. The model inter-comparison consists of an analysis of the spatial distribution of monthly mean concentrations and values for domain averaged model concentrations. The CAMS global model simu- lates in summer different spatial distribution due to the assimilation of satellite data providing information for dust storms and wildfires. Keywords Chemical transport models · Particulate matter · Model validation H. Kirova (B ) · N. Neykova · E. Georgieva National Institute of Meteorology and Hydrology (NIMH), 66, Tsarigradsko Shose Blvd Sofia, Sofia 1784, Bulgaria e-mail: hristina.kirova@meteo.bg N. Neykova e-mail: nadya.neykova@meteo.bg E. Georgieva e-mail: emilia.georgieva@meteo.bg © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 N. Dobrinkova and G. Gadzhev (eds.), Environmental Protection and Disaster Risks, Studies in Systems, Decision and Control 361, https://doi.org/10.1007/978-3-030-70190-1_8 107