BTEX, nitrogen oxides, ammonia and ozone concentrations at traffic influenced and background urban sites in an arid environment

Abstract

Spatial distribution of key air pollutants were studied in Doha, Qatar, over the course of two monitoring campaigns in early spring, 2016. Time-weighted averages of BTEX components (benzene, toluene, ethyl-benzene, (m+p)-xylene and o-xylene), as well as NO, NO2, ammonia and ozone were measured from February 29 to March 31 in two periods at 15 locations of the city concerning different types of environments such as background rural and suburban, as well as traffic emission influenced urban locations. Results show high variation of the concentration levels among the sampling locations. The average NOX concentration slightly exceeded the annual limit value (108 μg m−3 vs. 100 μg m−3), the exceedances were significant at locations highly influenced by traffic emission. Contrasting behavior was found for ozone concentration having the highest level at background locations (ranging from 36 to 71 μg m−3) and the lowest at the most polluted sites (12–30 μg m−3). BTEX concentrations were found slightly to be above the American and European levels, but far below the values reported from the MENA region. The average BTEX concentration was 15.3 μg m−3, peaking at 40.5 μg m−3 at the most polluted location. Average concentrations of benzene, toluene, ethyl-benzene, (m+p)-xylene and o-xylene were 1.5, 4.7, 2.0, 5.0 and 2.3 μg m−3 respectively. The average toluene to benzene ratio was 2.87, which confirms the traffic dominance of the emission. NO to NO2 ratio was used for the characterization of the photochemical age of the pollution and thus, indirectly the distance of the sources. The ratios ranged from 0.19 to 2.45. Despite the desert environment elevated average level of ammonia (17.6 μg m−3) was found. NH3 concentration was correlated with NOX that indicates same sources. Other hotspots like local animal market, as well as organic compost type fertilizer in a big public park were identified. These results indicate the dominance of vehicle emission in the formation of the city's air quality. Atmospheric modification of the components via photochemical reactions was found to be important.