Measuring the Building Envelope Penetration Factor for Ambient Nitrogen Oxides

Abstract

Much of human exposure to nitrogen oxides (NO x ) of ambient origin occurs indoors. Reactions with materials inside building envelopes are expected to influence the amount of ambient NO x that infiltrates indoors. However, envelope penetration factors for ambient NO x constituents have never been measured. Here, we develop and apply methods to measure the penetration factor and indoor loss rates for ambient NO x constituents using time-resolved measurements in an unoccupied apartment unit. Multiple test methods and parameter estimation approaches were tested, including natural and artificial indoor NO x elevation with and without accounting for indoor oxidation reactions. Twelve of 16 tests yielded successful estimates of penetration factors and indoor loss rates. The penetration factor for NO was confirmed to be ∼1 and the mean (±s.d.) NO 2 penetration factor was 0.72 ± 0.06 with a mean relative uncertainty of ∼15%. The mean (±s.d.) indoor NO 2 loss rate was 0.27 ± 0.12 h −1 , ranging 0.06−0.47 h −1 , with strong correlations with indoor relative and absolute humidity. Indoor NO loss rates were strongly correlated with the estimated ozone concentration in infiltrating air. Results suggest that envelope penetration factors and loss rates for NO x constituents can be reasonably estimated across a wide range of conditions using these approaches.

The atmospheric chemistry of indoor environments

“…NO + NO 2 ) will be from the polluted outdoor environment. 60 HONO can also be formed from gas stoves, giving mixing ratios of 10's of ppb in some cases. 21,59,61 However, even in the absence of combustion, reactive mechanisms (see Section 6c) can give rise to HONO mixing ratios in residential settings that are typically a few ppb, at least an order of magnitude higher than outside.…”

Indoor acids and bases

“…Zhao et al 220 recently investigated the building envelope penetration factors for ambient nitrogen oxides in an apartment in Chicago, IL. They found the penetration factor to be unity for NO and 0.72 ± 0.06 for NO 2 .…”

Combining homogeneous and heterogeneous chemistry to model inorganic compound concentrations in indoor environments: the H<sup>2</sup>I model (v1.0)

“…The building filtration factor controls the fluxes of outdoor pollutants that enter the room through the cracks and gaps of the building's structure. Its value derives from the routes available for transport and from the pollutant's reactivity with the materials of the building's enclosure assembly, which can scavenge components that are infiltrating (Zhao et al, 2019). Its value is component-specific and ranges from 0 (no intrusion) to 1.…”