Effect of Organic Coatings on Gas-Phase Nitrogen Dioxide Production from Aqueous Nitrate Photolysis

Abstract

The influence of stearic acid, octanol, and octanoic acid monolayer coatings on the release of NO 2 into the gas phase following aqueous NO 3 − photolysis was studied using incoherent broadband cavity-enhanced absorption spectroscopy (IBBC-EAS). The different organic compounds, when present at the aqueous surface, had varying effects on the gas-phase NO 2 evolved. Stearic acid monolayers lowered the initial rate of appearance of NO 2(g) , and its steady-state concentration was the same as for uncoated solutions after ∼50 min. In the presence of octanol monolayers, both the steady-state [NO 2(g) ] and its rate of appearance decreased. A simple kinetic phase partitioning model suggests that the rate of NO 2(g) evaporation from the aqueous surface is physically inhibited by the long uncompressed stearic acid chains, whereas both NO 2 evaporation and steady-state NO 2(g) concentration decrease when octanol is present at the aqueous surface, due to the enhanced solubility of NO 2 in the less polar octanol environment. Despite its structural similarity to octanol, monolayers of octanoic acid showed a different effect and slightly increased the steady-state [NO 2(g) ]. We propose that octanoic acid enhances NO 2(g) production because of an increase in solution acidity, which increases the quantum yield of NO 2 production from nitrate photolysis.

Formation of reactive nitrogen oxides from urban grime photochemistry

“…The increased reactivity could also be the result of a viscosity change within the film. It is known that the viscosity of particles changes based on relative humidity (Renbaum-Wolff et al, 2013), and therefore it is expected that the same would be true for grime, with particles being a source to the film. The film's water uptake/evaporation curve is consistent with continuous viscosity change rather than phase transitions over the RH region studied.…”

“…Gas phase product formation was determined using IB-BCEAS. The system is described in full elsewhere (Reeser et al, 2013). Briefly, a 10 W LED with a maximum intensity at 372 nm was focused into a 100 cm cell.…”

“…Transmission spectra were collected for 30 s (averages of 30 scans with an integration time of 1 s each) over a wavelength range of 362 to 385 nm. The concentrations of HONO and NO 2 were calculated using the method described by Fiedler and Gherman (Fiedler et al, 2003;Gherman et al, 2008) and previously used by us (Reeser et al, 2013). This uses measured mirror reflectivity (Washenfelder et al, 2008), Rayleigh cross sections of the carrier gas (Bodhaine et al, 2010) and the absorption cross sections of NO 2 (Vandaele et al, 1998) and HONO (Stutz et al, 2000) to fit the experimental spectra with DOASIS software (Lehmann, 2009).…”

Development of an incoherent broadband cavity enhanced absorption spectrometer for in situ measurements of HONO and NO<sub>2</sub> in China

“…However, Reeser et al (Reeser et al, 2013) and Scharko et al (Scharko et al, 2014) reckoned that the effect of the mirrors' purge flow on the final measured 10 concentration was negligible.…”

“…IBBCEAS has gradually been applied to the study of HONO Wu et al, 2011;Wu et al, 2014;Reeser et al, 2013;Scharko et al, 2014;Min et al, 10 2016),with continued improvements in sensitivity.…”