Air Quality Challenges in a Petrochemical Urban Area: Signatures of Pollution Sources and Atmospheric Conditions

Urban areas with industry focused on oil refining activities face significant challenges in air quality management due to complex interactions between local emissions, meteorology, and regional transport. The oil extraction and petrochemical industry in Ploiesti, Romania, played a pivotal role into the development of the country since 19^th century. This study investigates air pollution in Ploiesti area focusing on particulate matter (PM₁₀, PM_2.5) and key gaseous pollutants (NO, NO₂, SO₂, CO, VOCs, O₃) using hourly data sets from the city AQ Monitoring Network, local meteorological observations, and boundary layer data from the ERA5 reanalysis. For the medium term in-depth analysis of air pollutants, data were examined for a four year period (01.01.2018 - 31.12.2021), while for the long-term analysis statistical analysis was performed on a 16 year period (01.01.2007 - 31.12.2023).

The specific questions were targeted to the intra-urban variability of air pollutants versus the identification of city areas with similar pollution pattern, in relation with the meteorological observations; identification of emission sources (by source categories anthropogenic/natural); temporal patterns (daily, weekly, seasonal, annual) and trend quantifications; a check on the causes of pollution episodes (with respect to local sources or transport from medium to distant sources).

• The anthropogenic activity in Ploiesti strongly affects atmospheric pollution levels on daily timescales (PM_2.5/PM₁₀ = 0.71). However, high-resolution measurements reveal the specificity of the surroundings of the monitoring stations.
• The general temporal pattern of major pollutants (except O₃) with lower mass concentrations during warm periods and higher levels during colder seasons follows the general annual pattern of particulate emissions and is modulated by the meteorological seasonal variations (atmospheric mixing layer height).
• Particulate matter diurnal cycle indicates a peak during the morning rush hours (about 08:00-10:00) but no peak is clear in the afternoon/evening. This could possibly be related to the people social behavior in Ploiesti (i.e. social activities in parks and cafés, as well as various times for the job ending or shift works).
• We identified that the temporal patterns of O₃ precursors (elevated VOCs despite reduced NOx during weekends) in this mid-size city lead to the so-called O₃ weekday-weekend effect.
• From January 2018 to December 2021 a total of 36 pollution episodes were identified. It was found that local anthropogenic emissions coupled with boundary layer dynamics determined the occurrence of 42% of events, while the remaining (58%) are divided in almost equal parts between regional-scale events (27%) and events when dust advections coming from long distances (31%). The trends in the occurrence of pollution events are opposite: decreasing for local events and increasing for regional and LRT-determined events. This suggests that the large-scale air circulation patterns influenced by the higher energy in the atmosphere due to climate changes might alter the distribution and concentration of pollutants leading to fugitive air pollution events.

Acknowledgment: BM work was supported by the University of Bucharest, PhD research grant. Climate and meteorology data were extracted from https://cds.climate.copernicus.eu. Ground-level air pollution were extracted from Romanian National Air Quality Database, www.calitateaer.ro.