Assessment of air pollution and associated health risks in Central Tunisia (North Africa) during and outside Saharan dust events
摘要
This study examined the temporal variability of PM10, surface ozone (O3), NOx (NO + NO2) and CO in Kairouan (Central Tunisia), during May 2013 which was characterized by its very particular meteorology. The results showed that maximum daily concentrations of 467 µg/m3, 34 ppb and 39 ppb were recorded for PM10, surface O3 and NOx, respectively. The CO daily concentrations appeared almost constant, around 1.2 ppm. The PM10 individualized peaks occurring during May 1st–4th, 18th and 21st–22nd were attributed to the effect of severe Saharan dust storms associated with an intense subtropical cyclone threatening the most European regions. The recorded O3 concentrations and their nitrogen and carbon precursors were shown comparable, respectively, during and outside dust storm events. The O3 accumulation rate was approximately equal to 2 ppb/h. The rate coefficient (k3) for the NO-O3 reaction, and the NO2 photolysis rate j1, at 16:00 LTh, were found to be 17 ppm−1 min−1 and 0.25 min−1, respectively. Such values were slightly lower than that found in other Tunisian regions. PCA and HCA statistical approaches highlighted the O3 production processes through NO2 photolysis and CO oxidation, as well as its destruction due to NO titration and absorption. Multiple linear regression analysis revealed that wind speed and NO have the greatest influence on O3 concentrations variability. Air Quality Indices showed elevated values only during dust storm events, with PM10 contributing to AQI levels as high as 125, signaling poor air quality and heightened health risks during these episodes.