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. 2023 Jan 17;57(2):896-908.
doi: 10.1021/acs.est.2c05756. Epub 2023 Jan 5.

Measurements of Hydroxyl Radical Concentrations during Indoor Cooking Events: Evidence of an Unmeasured Photolytic Source of Radicals

Emily Reidy  1 , Brandon P Bottorff  1 , Colleen Marciel F Rosales  2 , Felipe J Cardoso-Saldaña  3 , Caleb Arata  4 , Shan Zhou  5 , Chen Wang  6 , Andrew Abeleira  7 , Lea Hildebrandt Ruiz  3 , Allen H Goldstein  4 , Atila Novoselac  8 , Tara F Kahan  5   9 , Jonathan P D Abbatt  6 , Marina E Vance  10 , Delphine K Farmer  7 , Philip S Stevens  1   2
Affiliations

Measurements of Hydroxyl Radical Concentrations during Indoor Cooking Events: Evidence of an Unmeasured Photolytic Source of Radicals

Emily Reidy et al. Environ Sci Technol. .

Abstract

The hydroxyl radical (OH) is the dominant oxidant in the outdoor environment, controlling the lifetimes of volatile organic compounds (VOCs) and contributing to the growth of secondary organic aerosols. Despite its importance outdoors, there have been relatively few measurements of the OH radical in indoor environments. During the House Observations of Microbial and Environmental Chemistry (HOMEChem) campaign, elevated concentrations of OH were observed near a window during cooking events, in addition to elevated mixing ratios of nitrous acid (HONO), VOCs, and nitrogen oxides (NOX). Particularly high concentrations were measured during the preparation of a traditional American Thanksgiving dinner, which required the use of a gas stove and oven almost continually for 6 h. A zero-dimensional chemical model underpredicted the measured OH concentrations even during periods when direct sunlight illuminated the area near the window, which increases the rate of OH production by photolysis of HONO. Interferences with measurements of nitrogen dioxide (NO2) and ozone (O3) suggest that unmeasured photolytic VOCs were emitted during cooking events. The addition of a VOC that photolyzes to produce peroxy radicals (RO2), similar to pyruvic acid, into the model results in better agreement with the OH measurements. These results highlight our incomplete understanding of the nature of oxidation in indoor environments.

Keywords: hydroxyl radical (OH); indoor oxidants; photochemistry.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Measurements from the 27 June Thanksgiving experiment. Orange-shaded regions indicate periods of gas cooking. (a) Temperature and relative humidity (b) alkene concentrations and both O3 instruments, with the KIT O3 divided by 10, (c) HONO and JHONO, (d) NO and both measurements of NO2, (e) measured HO2* and modeled HO2 concentrations from the base and high O3 scenarios (see text), and (f) measured and modeled OH concentrations from the base and high O3 scenarios. Green points in (f) indicate a period of increased human activity near the OH instrument, potentially creating a local OH sink or sink of photolytic precursors resulting in lower concentrations.
Figure 2
Figure 2
Measured concentrations and environmental parameters for the 12 June repeated cooking events. Measurements include temperature, relative humidity (a), O3, alkenes (b), HONO, light (c), NO, NO2 (d), HO2* (e), and OH (f). Modeled concentrations from the base model are also shown in (e, f). Blue-shaded regions indicate ventilation periods while orange-shaded regions indicate the use of the gas stove.
Figure 3
Figure 3
Measured OH concentrations plotted against indoor sources (a) and indications of potential LP/LIF instrument interferences (HONO (b), JHONO (c), laser power (d), monoterpenes (e), O3 (f), and the product of O3 and monoterpenes (g)) during the 27 June Thanksgiving experiment. Points when guests arrived (15:30–17:30) were omitted. The strong correlation with HONO photolysis compared to weak correlations with interference precursors suggest that the measurements do not suffer from interferences. In panel a, JHONO × [HONO] was calculated using LP/LIF values for HONO.
Figure 4
Figure 4
Calculated photolysis frequencies of the interfering species (JINT, right axis) based on measurements during 8 June (red points) and 25 June (blue points) with all of the measured JHONO values from the entire campaign (small dots, left axis) as a function of time of day. Bimodal distribution is due to individual measurements from the two main windows, one facing east in the kitchen (green dots) and one facing west in the living room (gray dots).
Figure 5
Figure 5
Measurements of HO2* (a and b) and OH (c and d) during cooking events. Model results for the base case (blue) and with an additional photolytic VOC with a maximum concentration of 1 ppb (red) and 10 ppb (purple) for the 27 June Thanksgiving experiment (a and c) and the 12 June Repeated Cooking event (b and d). Variations in the concentration of the photolytic VOC were scaled to the difference in signals between the O3 instruments for the Thanksgiving experiment, and the ratio of interference/NO2 was subsequently used to constrain the 12 June model (see text). Occupancy of the house is indicated by the color of the points, with red points when 3–4 people were present, green points with 13 people present, and unoccupied times in black points. The shading of the 12 June model represents a model run with the photolytic VOC changed by ±50%.
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