Photoenhanced uptake of NO2 on soot

B. D'ANNA; C. GEORGE; M. MONGE; M. AMMANN; D. J. DONALDSON

San Francisco

Conferencia; AGU Fall Meeting 2009; 2009

Soot was suggested to be an important sink for some atmospheric oxidants (such as O3 or NOx), as a consequence its chemistry has been largely investigated in the past years. However, the atmospheric impact of that appeared to be quite limited because of a rapid soot surface passivation. However, most of the previous studies were done under dark conditions. We therefore investigated whether the uptake kinetics of NO2 is enhanced once the soot surface is illuminated with UV light. These experiments were performed by means of a a coated flow tube equipped with near-UV emitting lamps. Different combustion conditions were used for producing the soot samples. We determined the uptake coefficients for different gas phase NO2 concentrations (15 -120 ppbv) in the dark and under near UV irradiation. The results show that the NO2 uptake on soot is considerably enhanced under irradiation leading to NO and HONO production. Uptake coefficients increased both with soot mass and the irradiation intensity. The inverse dependence of the uptake coefficient with the NO2 concentration, both under illumination and in the dark, was consistent with a Langmuir-Hinshelwood mechanism. HONO yields change according to the combustion conditions of soot particles. The importance of soot photochemistry will presented and discussed as our results suggest that photo-induced uptake can be important under atmospheric conditions with respect irradiance, humidity, temperature and gas trace mixing ratio.