Heterogeneous conversion of NO<sub>2</sub> and NO on HNO<sub>3</sub> treated soot surfaces: atmospheric implications

Abstract

Abstract. In the present study, the heterogeneous conversion of nitrogen oxide (NO) and nitrogen dioxide (NO 2 ) was studied at atmospheric humidity levels on flame soot surfaces treated with gaseous nitric acid (HNO 3 ). In addition, the heterogeneous reaction of HNO 3 on soot was investigated at atmospheric humidity.For the treatment of soot by pure HNO 3 only reversible uptake with a surface coverage of ∼1-2×10 14 HNO 3 cm −2 was observed for HNO 3 mixing ratios in the range 250-800 ppbv. Only for higher HNO 3 mixing ratios of >800 ppbv the formation of NO and NO 2 was observed. The results were not affected by the addition of NO. In none of the experiments with HNO 3 the formation of nitrous acid (HONO) was observed. For HNO 3 mixing ratios <600 ppbv the upper limit yields for HONO, NO 2 and NO were found to be <0.2%, <0.5% and <1%, respectively. Compared to untreated soot, the product formation of the reaction of NO 2 with soot was not significantly affected when the soot surface was treated with gaseous HNO 3 prior to the experiment. Only for high surface coverage of HNO 3 the formation of HONO was suppressed in the initial phase of the reaction, probably caused by the blocking of active sites by adsorbed HNO 3 .Under the assumption that the experimental findings for the used model flame soot can be extrapolated to atmospheric soot particles, the results show that the reactions of HNO 3 and HNO 3 +NO on soot surfaces are unimportant for a "renoxification" of the atmosphere and do not represent an atmospheric HONO source. In addition, the integrated HONO yield of ca. 10 14 cm −2 in the reaction of NO 2 with soot is not significantly influenced by simulated atmospheric processing of the soot surface by HNO 3 , and is still too small to explain HONO formation in the atmosphere.

Impact of HONO sources on the performance of mesoscale air quality models

“…Studies using different vehicles and engine tests have shown that HONO to NO x emission ratios range from 0.01% to 1.8% (Kurtenbach et al, 2001), depending on the vehicle and fuel type, and the oxygen content. Generally, diesel vehicles under rich operation conditions lead to higher HONO/NO x ratios than gasoline-fuelled vehicles under lean operation conditions (Kurtenbach et al, 2001).…”

“…Heterogeneous conversion of nitric acid (HNO 3 ) on primary organic aerosols (Ziemba et al, 2010) or ground surfaces (RiveraFigueroa et al, 2003) yields HONO, however those reactions have been recently discredited under atmospheric conditions (Kleffmann et al, 2004;Kleffmann and Wiesen, 2005). Other works (e.g.…”

“…Homogeneous gas-phase chemistry (Platt et al, 1980) alone fails to capture the observed HONO profiles (Calvert et al, 1994;Winer and Biermann, 1994;Kurtenbach et al, 2001). Thus, other direct and indirect sources of HONO must be accounted for to bridge the gap between modeling studies and ambient measurements.…”

“…One proposed pathway for HONO formation in the atmosphere is the hydrolysis of NO 2 on wet surfaces (Kleffmann et al, 1998;Kurtenbach et al, 2001;Stutz et al, 2004):…”

Exploring Possible Missing Sinks of Nitrate and Its Precursors in Current Air Quality Models —A Case Simulation in the Pearl River Delta, China, Using an Observation-Based Box Model

“…Recently, a heterogeneous reaction of HNO 3 on soot (R1) was proposed to explain the overestimation of HNO 3 / NO x in simulations (Rogasi et al 1997). This mechanism has been successfully applied in some studies, although it has still to be confirmed in laboratory studies (Hauglustaine et al 1996;Kleffmann and Wiesen 2005). Many uptake coefficients for R1 (γ HNO3 ), ranging from 10 −7 to 10 −2 , have been proposed based on laboratory and model experiments (Hauglustaine et al 1996;Rogasi et al 1997), and therefore studies of γ HNO3 that are appropriate for the soot aerosol morphology in China are needed.…”