Characterization of Photochemical Processes in Doha, Qatar.

The research focused on the air quality of the air shed of Doha, Qatar; characterizing its photochemistry and interaction between gases, particles, and meteorological conditions. Data from an air quality monitoring station for the year 2015 was used. These consisted of meteorological measurements in addition to ozone (O3), nitrogen monoxide (NO), direct nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), as well as particulate matter with an aerodynamic diameter ≤ 10 µm and 2.5 µm (PM10 and PM2.5). In addition, two Intensive Observational Periods (IOP) were performed, one in winter and one in summer, where nitrous acid (HONO), formaldehyde (HCHO), and speciated photolysis rates (SPRs) were measured. These were used to calculate hydroxyl radical (·OH) production and its precursor’s contributions, the air shed’s ozone production-sensitivity variability, and to elucidate sources of these radical precursors. Three main meteorological seasons were identified in the city, a Cool (Co) (20.8 °C median Temperature (T)), a Hot & Dry (HD) (33.7 °C median T, 9.6 g/m3 median absolute humidity (AH)), and a Hot & Dry (HD) (34.0 °C median T, 18.9 g/m3 median AH). A pronounced land-sea-breeze circulation was observed during HW. NO, CO, NO2, PM10 and PM2.5 showed pronounced peaks during the morning traffic rush hour in all seasons. CO showed two times higher concentrations during HW while SO2 showed 50 % lower concentrations compared to HD and Co. PM10 was 42.3 % higher during weekdays than on weekends and was strongly correlated with wind speed. During the winter IOP ozone formation was always VOC sensitive, while during the summer IOP, ozone formation became NO2 sensitive around noon time (about 6 % of the entire time). The photolysis of HONO was the main precursor for ·OH production with 54.3 % and 72.7 % (summer and winter), while the photolysis of ozone was responsible for 23.8 % and 19.7 % and the photolysis of HCHO accounted for 21.9 % and 7.6 % (summer and winter respectively). HONO production from NO2 reaction over soot dominated its sources during the night. For traffic-related HONO emissions, a HONO/NOx emission ratio of 0.009 Kg/Kg (R2 = 0.95) was determined. HCHO sources were found to be 65.7 % traffic, 20.7 % industrial, 12.3 % photochemical, and 1.3 % unaccounted.