Local and regional air pollution characteristics in Cyprus: A long-term trace gases observations analysis

• Published in: The Science of the total environment 2022-11, Vol.845, p.157315-157315, Article 157315
• Main Authors: Vrekoussis, M., Pikridas, M., Rousogenous, C., Christodoulou, A., Desservettaz, M., Sciare, J., Richter, A., Bougoudis, I., Savvides, C., Papadopoulos, C.
• Format: Article
• Language: English
• Subjects: Eastern Mediterranean and Middle East region (EMME); In situ trace gases observations; Local vs. regional pollution; Pollution hotspots; Satellite observations
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.157315

Observations of key gaseous trace pollutants, namely NO, NOy, CO, SO2 and O3, performed at several curb, residential, industrial, background and free-troposphere sites were analyzed to assess the temporal and spatial variability of pollution in Cyprus. Notably, the analysis utilized one of the longest datasets of 17 years of measurements (2003–2019) in the East Mediterranean and the Middle East (EMME). This region is considered a regional hotspot of ozone and aerosol pollution. A trend analysis revealed that at several stations, a statistically significant decrease in primary pollutant concentration is recorded, most likely due to pollution control strategies. In contrast, at four stations, a statistically significant increase in ozone levels, ranging between 0.36 ppbv y−1 and 0.82 ppbv y−1, has been observed, attributed to the above strategies targeting the reduction of nitrogen oxides (NOx) but not that of Volatile Organic Compounds (VOCs). The NO and NOy, and CO levels at the Agia Marina regional background station were two orders of magnitude and four times lower, respectively, than the ones of the urban centers. The latter denotes that local emissions are not negligible and control a large fraction of the observed interannual and diurnal variability. Speciation analysis showed that traffic and other local emissions are the sources of urban NO and NOy. At the same time, 46 % of SO2 and 40 % of CO, on average, originate from long-range regional transport. Lastly, a one-year analysis of tropospheric NO2 vertical columns from the TROPOMI satellite instrument revealed a west-east low-to-high gradient over the island, with all major hotspots, including cities and powerplants, being visible from space. With the help of an unsupervised machine learning approach, it was found that these specific hotspots contribute overall around 10 % to the total NO2 tropospheric columns. Local vs. Regional pollution at the urban centers in Cyprus: Decreasing trends of trace pollutants [NO, NOz, CO and SO2] are observed for the years considered in this study (2003–2019) at the major urban centers of Cyprus, possibly associated with pollution mitigation strategies. In contrast, ozone has either remained constant or increased in those VOC-limited urban regimes. The largest fraction of NO and NOz in these cities emanates from local traffic and/or background urban sources (top panel, grey bars) while, at the same time, a large fraction of the observed SO2 and CO of around 40 % an