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

Observations of key gaseous trace pollutants, namely NO, NO_y, CO, SO₂ and O_3, 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 ppb_v y^-1 and 0.82 ppb_v y^-1_, has been observed, attributed to the above strategies targeting the reduction of nitrogen oxides (NO_x) but not that of Volatile Organic Compounds (VOCs). The NO and NO_y, 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 NO_y. 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.