Abstract
Abstract. Nitrous acid (HONO) plays a key role in atmospheric chemistry by influencing the budget of hydroxyl radical (OH). In this study, a two-month measurement of HONO and related quantities were analyzed during a biomass burning season in 2012 at a suburban site in the western Yangtze River delta, eastern China. An overall high HONO concentration with the mean value of 0.76 ppbv (0.01 ppbv to 5.95 ppbv) was observed. During biomass burning (BB) periods, both HONO concentration and HONO/NO2 ratio were enhanced significantly (more than a factor of 2, p < 0.01) compared with non-biomass burning (non-BB) periods. A correlation analysis showed that the HONO in BB plumes was more correlated with nitrogen dioxide (NO2) than that with potassium (a tracer of BB). Estimation by the method of potassium tracing suggests a maximum contribution of 17 ± 12% from BB emission to the observed HONO concentrations, and the other over 80% of the observed nighttime HONO concentrations during BB periods were secondarily produced by the heterogeneous conversion of NO2. The NO2-to-HONO conversion rate (CHONO) in BB plumes was almost twice as that in non-BB plumes (0.0062 hr−1 vs. 0.0032 hr−1). Given that the residence time of the BB air masses was lower than that of non-BB air masses, these results suggest BB aerosols have higher NO2 conversion potentials to form HONO than non-BB aerosols. A further analysis based on comparing the surface area at similar particle mass levels and HONO/NO2 ratios at similar surface area levels suggested larger specific surface areas and higher NO2 conversion efficiencies of BB aerosols. A mixed plume of BB and anthropogenic fossil fuel (FF) emissions was observed on 10 June with even higher HONO concentrations and HONO/NO2 ratios. The strong HONO production potential (high HONO/NO2 to PM2.5 ratio) was accompanied with a high sulfate concentration in this plume, suggesting a promotion of mixed aerosols to the HONO formation. In summary, our study suggests an important role of BB in atmospheric chemistry by affecting the HONO budget. This can be especially important in eastern China, where agricultural burning plumes are inevitably mixed with urban and industrial pollution.
Highlights
Nitrous acid (HONO) is an important constituent in the troposphere due to its role in hydrogen oxide (HOx) cycling (Platt et al, 1980; Kleffmann, 2007; Hofzumahaus et al, 2009; Elshorbany et al, 2012)
HONO concentrations increased by 156 % (1.56 ± 1.43 ppbv vs. 0.61 ± 0.54 ppbv, p
The NO2-to-HONO (CHONO) conversion rates were detected to be significantly elevated during the biomass burning (BB) periods due to the combined effect of enhanced particle loadings, larger specific surface areas of particles and higher NO2 conversion efficiency on BB aerosols
Summary
Nitrous acid (HONO) is an important constituent in the troposphere due to its role in hydrogen oxide (HOx) cycling (Platt et al, 1980; Kleffmann, 2007; Hofzumahaus et al, 2009; Elshorbany et al, 2012). As one major component in BB plumes, have been demonstrated to be an effective media to convert NO2 to HONO (Kleffmann et al, 1999; Aumont et al, 1999; Prince et al, 2002; Kleffmann and Wiesen, 2005; Aubin and Abbatt, 2007), especially in the case that aged soot particles can be re-activated in the present of light (Monge et al, 2010) and play a continuous role in the HONO chemistry These processes may significantly influence the HONO chemistry during a BB period, but their exact roles are rarely demonstrated in the real atmosphere, especially when BB aerosols are mixed with anthropogenic pollutants. The influences of mixed plumes of intensive BB and FF emission (Ding et al, 2013b) on HONO formation were discussed
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