Loss of NO(g) to painted surfaces and its re‐emission with indoor illumination

Abstract

Heterogeneous surface reactions play a key role in the chemistry of the indoor environment because of the large indoor surface‐to‐volume ratio. The presence of photocatalytic material in indoor paints may allow photochemical reactions to occur at wavelengths of light that are present indoors. One such potential reaction is the heterogeneous photooxidation of NO to HONO. NO(g) is commonly found indoors, originating from combustion sources, ventilation and infiltration of outdoor air. We studied the interaction of NO(g) with painted surfaces illuminated with indoor fluorescent and incandescent lighting. There is a loss of NO(g) to painted surfaces in the dark at both 0 and 50% RH. At 50% RH, there is a re‐release of some of that NO(g) under illumination. The same behavior is observed for illumination of different colored paints. This is in contrast to what is seen with TiO2 as the substrate, where photoenhanced uptake of NO(g) and formation of NO2(g) are observed. We hypothesize that the loss of NO(g) is due to adsorption and diffusion into the paint. The re‐release of NO under illumination is thought to be due to photooxidation of NO to HONO on the painted surface at higher relative humidities and subsequent HONO photolysis.

Spatiotemporal characterization of irradiance and photolysis rate constants of indoor gas‐phase species in the UTest house during HOMEChem

“…The few published studies on indoor surface photochemistry indicate that surface photolysis could also contribute to the oxidative capacity indoors and influence indoor air composition, especially near surfaces such as painted walls 15,16,18,46,47 . However, surface photochemical reaction rates remain almost completely unquantified.…”

“…Mixing ratios of HOCl, Cl capacity indoors and influence indoor air composition, especially near surfaces such as painted walls. 15,16,18,46,47 However, surface photochemical reaction rates remain almost completely unquantified. Photon fluxes at surfaces are one of the many uncertainties surrounding this chemistry.…”

Reactive Uptake of Gas-Phase NO2 by Urban Road Dust in the Dark

“…8,11 Overall, NO x is partially responsible for urban smog, as well as acid rain and other pollution events harmful to human health. 12 Dirty city surfaces are known to be effective at recycling NO x ; 13,14 for example, Baergen and Donaldson 14 showed that heterogeneous photochemistry of nitrate anions present in the film of atmospheric constituents deposited onto urban surfaces (known as urban grime) produces NO x and other reactive species. Photochemical, humidity-dependent uptake of NO 2 onto urban grime has also been reported as a significant source of HONO, which could affect the oxidative capacity of the daytime urban atmosphere.…”

“…Atmospheric gases such as NO x (NO 2 and NO) are produced outdoors through the combustion of fossil fuels and are present in urban atmospheres at or up to several hundred parts per billion by volume. − Reactions involving NO x and VOCs are responsible for the production of tropospheric ozone (O 3 ); furthermore, NO x is a precursor to HONO, which is a photochemical source of OH radicals under illumination conditions where O 3 chemistry is not important. , Overall, NO x is partially responsible for urban smog, as well as acid rain and other pollution events harmful to human health . Dirty city surfaces are known to be effective at recycling NO x ; , for example, Baergen and Donaldson showed that heterogeneous photochemistry of nitrate anions present in the film of atmospheric constituents deposited onto urban surfaces (known as urban grime) produces NO x and other reactive species. Photochemical, humidity-dependent uptake of NO 2 onto urban grime has also been reported as a significant source of HONO, which could affect the oxidative capacity of the daytime urban atmosphere. , In addition, NO x reacts heterogeneously with mineral dust, , a major component of road dust. , In this reaction, NO 2 first adsorbs to the surface of the dust, then produces gas-phase NO and nitrate. , Finally, road dust itself has recently been shown to be photochemically active; it can produce singlet oxygen upon illumination when in aqueous suspended state, which suggests the potential for heterogeneous photochemistry.…”