Abstract
Ground ozone (O3) is a major photochemical air pollutant that has negative effects on both human health and environment, exposure to which results in the development of respiratory diseases and damage to ecosystems. Ozone does not have direct natural or anthropogenic sources of emission and its formation is accounted for the cyclic photochemical reaction between its precursors, nitrogen dioxide (NO2) and volatile organic compounds (VOC). This study investigated ozone concentration and chemistry over Syrian cities Deir ez-Zor and Aleppo between 2005 and 2016. These two cities experienced a civil war in 2011 that later on involved other countries. To identify how the trends of NO2 and VOC were changed due to the war, and subsequently their effect on the ozone formation, the study was divided into two periods, before and after the war. This study was conducted by analyzing Formaldehyde-to-Nitrogen Dioxide ratio (FNR), which is considered to be the main indicator of ozone sensitivity regime. It was observed that starting the war, Aleppo, located on the west of Syria experienced a change of FNR values from the range of 0-1 to 1-2 which represents a shift in ozone sensitivity regime. The city located on the east of the country, Deir ez-Zor, did not experience a considerable change in the regime, as FNR values were maintained above 2 throughout the given period. Such different responses to the presence of the war in the cities of the same country could emphasize that the war has variant effects on the ozone chemistry over the cities due to the intensity of the war interactions and background of the cities. Lastly, it was found that changes in ozone chemistry in Syria due to the war resulted in the similar changes in ozone chemistry in the bordering countries (Turkey and Lebanon), and thus areas of these countries which are close to the borders of Syrian Arab Republic experienced ozone peaks in 2012 and 2016 due to the sharp increases of ozone in Syria itself.