The House Observations of Microbial and Environmental Chemistry (HOMEChem) study was a large-scale collaborative experimental investigation probing indoor air composition and chemistry.

We report elevated levels of gaseous inorganic chlorinated and nitrogenated compounds in indoor air while cleaning with a commercial bleach solution during the House Observations of Microbial and Environmental Chemistry field campaign in summer 2018. Hypochlorous acid (HOCl), chlorine (Cl2), and nitryl chloride (ClNO2) reached part-per-billion by volume levels indoors during bleach cleaningseveral orders of magnitude higher than typically measured in the outdoor atmosphere. Kinetic modeling revealed that multiphase chemistry plays a central role in controlling indoor chlorine and reactive nitrogen chemistry during these periods. Cl2 production occurred via heterogeneous reactions of HOCl on indoor surfaces. ClNO2 and chloramine (NH2Cl, NHCl2, NCl3) production occurred in the applied bleach via aqueous reactions involving nitrite (NO2 –) and ammonia (NH3), respectively. Aqueous-phase and surface chemistry resulted in elevated levels of gas-phase nitrogen dioxide (NO2). We predict hydroxyl (OH) and chlorine (Cl) radical production during these periods (106 and 107 molecules cm–3 s–1, respectively) driven by HOCl and Cl2 photolysis. Ventilation and photolysis accounted for <50% and <0.1% total loss of bleach-related compounds from indoor air, respectively; we conclude that uptake to indoor surfaces is an important additional loss process. Indoor HOCl and nitrogen trichloride (NCl3) mixing ratios during bleach cleaning reported herein are likely detrimental to human health.

Hourly measurements of 46 volatile organic compounds (VOCs) from the Boulder Atmospheric Observatory in Erie, CO, were collected over 16 weeks in spring and summer 2015. Average VOC reactivity (1.2 s−1 in spring and 2.4 s−1 in summer) was lower than most other U.S. urban sites. Positive matrix factorization analysis identified five VOC factors in the spring, corresponding to sources from (1) long‐lived oil and natural gas (ONG‐long lived), (2) short‐lived oil and natural gas (ONG‐short lived), (3) traffic, (4) background, and (5) secondary chemical production. In the summer, an additional biogenic factor was dominated by isoprene. While ONG‐related VOCs were the single largest contributor (40–60%) to the calculated VOC reactivity with hydroxyl radicals (OH) throughout the morning in both spring and summer, the biogenic factor substantially enhanced afternoon and evening (2–10 P.M. local time) VOC reactivity (average of 21%; maxima of 49% of VOC reactivity) during summertime. These results contrast with a previous summer 2012 campaign which showed that biogenics contributed only 8% of VOC reactivity on average. The interannual differences suggest that the role of biogenic VOCs in the Colorado Northern Front Range Metropolitan Area (NFRMA) varies with environmental conditions such as drought stress. Overall, the NFRMA was more strongly influenced by ONG sources of VOCs than other urban and suburban regions in the U.S.

Bleach can oxidize volatile organic compounds (VOCs) and contribute to secondary organic aerosol (SOA) indoors. During the House Observations of Microbial and Environmental Chemistry (HOMEChem) campaign, we observed indoor terpene mixing ratios decrease during bleach cleaning periods, with simultaneous increases in oxidized VOC (OVOC) products. Cooking just prior to bleach cleaning significantly increased SOA due to uptake of bleach-related OVOCs onto cooking aerosols. While SOA formation occurred, it was small (<3%) relative to total organic aerosol mass concentrations. Bleach cleaning chemistry also produced several potentially toxic chlorinated and nitrogenated VOCs indoors, including isocyanates, cyanogen chloride, and chlorocarbons. Observed volatile chlorinated organic acids were likely impurities from the bleach. The bleach-induced terpene oxidation, SOA formation, and chlorinated/nitrogenated VOC production were independent of indoor illumination, consistent with dark chemical production. These observations add to previous studies that demonstrate bleach as a source of potentially harmful primary and secondary pollutants to indoor air.

Abstract. The relative importance of wildfire smoke for air quality over the western US is expected to increase as the climate warms and anthropogenic emissions decline. We report on in situ measurements of ozone (O 3 ), a suite of volatile organic compounds (VOCs), and reactive oxidized nitrogen species collected during summer 2015 at the Boulder Atmospheric Observatory (BAO) in Erie, CO. Aged wildfire smoke impacted BAO during two distinct time periods during summer 2015: 6-10 July and 16-30 August. The smoke was transported from the Pacific Northwest and Canada across much of the continental US. Carbon monoxide and particulate matter increased during the smoke-impacted periods, along with peroxyacyl nitrates and several VOCs that have atmospheric lifetimes longer than the transport timescale of the smoke. During the August smokeimpacted period, nitrogen dioxide was also elevated during the morning and evening compared to the smoke-free periods. There were nine empirically defined high-O 3 days during our study period at BAO, and two of these days were smoke impacted. We examined the relationship between O 3 and temperature at BAO and found that for a given temperature, O 3 mixing ratios were greater (∼ 10 ppbv) during the smoke-impacted periods. Enhancements in O 3 during the August smoke-impacted period were also observed at two long-term monitoring sites in Colorado: Rocky Mountain National Park and the Arapahoe National Wildlife Refuge near Walden, CO. Our data provide a new case study of how aged wildfire smoke can influence atmospheric composition at an urban site, and how smoke can contribute to increased O 3 abundances across an urban-rural gradient.