Photoenhanced uptake of NO2 on soot

M. E. MONGE; B. D'ANNA; C. GEORGE

Conferencia; 19th Annual VM Goldschmidt Conference; 2009

Soot was suggested to be an important sink for some atmospheric oxidants (such as O3 or NOx). As a consequence, its heterogeneous chemistry has been largely investigated in the past years. However, its atmospheric impact appeared to be quite limited due to a rapid soot surface passivation. As previous studies were done under dark conditions, we decided to investigate the effect of light on the uptake kinetics of NO2 on soot. These experiments were performed by means of a coated flow tube equipped with near-UV emitting lamps. Different combustion conditions were used to produce 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 showed 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 changed accordingly to the combustion conditions of soot particles. The importance of soot photochemistry will be presented and discussed as our results suggest that photo-induced uptake may be important under atmospheric conditions.