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. 2022 Oct 4;56(19):13573-13583.
doi: 10.1021/acs.est.2c02196. Epub 2022 Sep 22.

Comparison of Simultaneous Measurements of Indoor Nitrous Acid: Implications for the Spatial Distribution of Indoor HONO Emissions

Brandon Bottorff  1   2 , Chen Wang  3   4 , Emily Reidy  1 , Colleen Rosales  2   5 , Delphine K Farmer  6 , Marina E Vance  7 , Jonathan P D Abbatt  3 , Philip S Stevens  1   2
Affiliations

Comparison of Simultaneous Measurements of Indoor Nitrous Acid: Implications for the Spatial Distribution of Indoor HONO Emissions

Brandon Bottorff et al. Environ Sci Technol. .

Abstract

Despite its importance as a radical precursor and a hazardous pollutant, the chemistry of nitrous acid (HONO) in the indoor environment is not fully understood. We present results from a comparison of HONO measurements from a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) and a laser photofragmentation/laser-induced fluorescence (LP/LIF) instrument during the House Observations of Microbial and Environmental Chemistry (HOMEChem) campaign. Experiments during HOMEChem simulated typical household activities and provided a dynamic range of HONO mixing ratios. The instruments measured HONO at different locations in a house featuring a typical air change rate (ACR) (0.5 h-1) and an enhanced mixing rate (∼8 h-1). Despite the distance between the instruments, measurements from the two instruments agreed to within their respective uncertainties (slope = 0.85, R2 = 0.92), indicating that the lifetime of HONO is long enough for it to be quickly distributed indoors, although spatial gradients occurred during ventilation periods. This suggests that emissions of HONO from any source can mix throughout the house and can contribute to OH radical production in sunlit regions, enhancing the oxidative capacity indoors. Measurement discrepancies were likely due to interferences with the LP/LIF instrument as well as calibration uncertainties associated with both instruments.

Keywords: indoor air chemistry; indoor air pollution; indoor emissions; photolysis; radical production; ventilation.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Floorplan of the UTest house with the CIMS (blue) and LP/LIF (red) sampling locations highlighted.
Figure 2
Figure 2
Time series of all HONO measurements during HOMEChem by the CIMS instrument (blue) and the LP/LIF instrument (red).
Figure 3
Figure 3
CIMS (blue) and LP/LIF (red) measurements of HONO from Thanksgiving experiments on (a) June 18 and (b) June 27. Shaded regions indicate active propane-cooking periods. A bivariate weighted fit of the data is also shown with the regression slope (m) and y-intercept (b) (see text).
Figure 4
Figure 4
CIMS (blue) and LP/LIF (red) as well as the ratio of the CIMS and LP/LIF measurements of HONO from a sequential cooking experiment on June 6. Shaded areas indicate ventilation (blue) and active propane (orange) and electric hotplate (purple) cooking experiments. Measurements during ventilation periods are not included in the correlation (see text).
Figure 5
Figure 5
CIMS (blue) and LP/LIF (red) measurements of HONO as well as the ratio of the CIMS and LP/LIF measurements, and HOCl measurements from a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) paired with iodide (I–) chemical ionization (green) from (a) sequential bleach cleaning experiments (June 10) and (b) a layered experiment (June 19). Blue-, green-, and orange-shaded regions represent ventilation, bleach cleaning, and cooking periods, respectively. Measurements when HOCl was high (green triangles), measurements during ventilation periods (blue triangles), and LP/LIF measurements corrected for the HOCl interference (open red circles) are not included in the correlation analysis (see text).
Figure 6
Figure 6
CIMS (blue), LP/LIF (red), and the ratio of the CIMS and LP/LIF measurements of HONO mixing during ventilation experiments (blue-shaded regions) on June 4 and 20. Measurements during ventilation periods are not included in the correlation analysis.
Figure 7
Figure 7
Correlation plot of all common measurements between the CIMS and LP/LIF instruments during HOMEChem. Gray triangles indicate measurements from the Thanksgiving experiment on June 18, during which measured mixing ratios were significantly higher than all other measurements during the campaign, and blue triangles indicate measurements during enhanced ventilation periods. These measurements, along with a small number of measurements during bleach cleaning experiments when HOCl likely interfered with the LP/LIF instrument, are not included in the correlation analysis.
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