From the HOMEChem frying pan to the outdoor atmosphere: chemical composition, volatility distributions and fate of cooking aerosol.

Cooking organic aerosol (COA) is frequently observed in urban field studies. Like other forms of organic aerosol, cooking emissions partition between gas and particle phases; a quantitative understanding of the species volatility governing this partitioning is essential to model the transport and fate of COA. However, few cooking-specific volatility measurements are available, and COA is often assumed to be semi-volatile. We use measurements from a thermodenuder coupled to an aerosol chemical speciation monitor during the HOMEChem study to investigate the chemical components and volatility of near-source COA. We found that fresh emissions of COA have three chemical components: a biomass burning-like component (COABBOA), a lower volatility component associated with cooking oil (COAoil-2), and a higher volatility component associated with cooking oil (COAoil-1). We provide characteristic mass spectra and volatility profiles for these components. We develop a model to describe the partitioning of these emissions as they dilute through the house and outdoor atmosphere. We show that the total emissions from cooking can be misclassified in air quality studies that use semi-volatile emissions as a proxy for cooking aerosol, due to the presence of substantial mass in lower volatility bins of COA not generally represented in models. Primary emissions of COA can thus be not only primary sources of urban aerosol pollution, but also sources of semi-volatile organic compounds that undergo secondary chemistry in the atmosphere and contribute to ozone formation and secondary organic aerosol.

Fates and spatial variations of accumulation mode particles in a multi-zone indoor environment during the HOMEChem campaign.

Studying the indoor dynamics that impact particles is crucial in order to understand indoor air chemistry and assess overall human exposure to particles. This work investigates spatial gradients in particle concentration, caused by indoor transport and loss mechanisms. We conducted a variety of cooking experiments during the House Observations of Microbial and Environmental Chemistry (HOMEChem) campaign in June 2018 that allowed us to probe these mechanisms. We measured size-resolved (0.06-1 µm and 0.13-3 µm) particle number concentrations from cooking experiments using optical instruments at four locations throughout the house simultaneously. The particle number concentration in the kitchen was 40 ± 10% and 70 ± 10% higher than the concentrations in the living room and the bedroom, respectively. There was a minor size dependence, with larger differences in the smaller sizes of the accumulation mode (0.1-2.5 µm) than the larger end of the range. Dilution accounts for the majority of these concentration differences. Surface deposition was the dominant fate of particles within a zone, with observed deposition velocities ranging from 0.1 to 0.6 m h-1.

Dry Deposition of Atmospheric Aerosols: Approaches, Observations, and Mechanisms.

Aerosols are liquid or solid particles suspended in the atmosphere, typically with diameters on the order of nanometers to microns. These particles impact air quality and the radiative balance of the planet. Dry deposition is a key process for the removal of aerosols from the atmosphere and plays an important role in controlling the lifetime of atmospheric aerosols. Dry deposition is driven by turbulence and shows a strong dependence on particle size. This review summarizes the mechanisms behind aerosol dry deposition, including measurement approaches, field observations, and modeling studies. We identify several gaps in the literature, including deposition over the cryosphere (i.e., snow and ice surfaces) and the ocean; in addition, we highlight new techniques to measure black carbon fluxes. While recent advances in aerosol instrumentation have enhanced our understanding of aerosol sources and chemistry, dry deposition and other loss processes remain poorly investigated.

Indoor emissions of total and fluorescent supermicron particles during HOMEChem.

Inhalation of particulate matter is associated with adverse health outcomes. The fluorescent portion of supermicron particulate matter has been used as a proxy for bioaerosols. The sources and emission rates of fluorescent particles in residential environments are not well-understood. Using an ultraviolet aerodynamic particle sizer (UVAPS), emissions of total and fluorescent supermicron particles from common human activities were investigated during the HOMEChem campaign, a test-house investigation of the chemistry of indoor environments. Human occupancy and activities, including cooking and mopping, were found to be considerable sources of indoor supermicron fluorescent particles, which enhanced the indoor particle concentrations by two orders of magnitude above baseline levels. The estimated total (fluorescent) mass emission rates for the activities tested were in the range of 4-30 (1-11) mg per person meal for cooking and 0.1-4.9 (0.05-4.7) mg/h for occupancy and mopping. Model calculations indicate that, once released, the dominant fate of coarse particles (2.5-10 micrometer in diameter) was deposition onto indoor surfaces, allowing for the possibility of subsequent resuspension and consequent exposures over durations much longer than the ventilation time scale. Indoor coarse particle deposition would also contribute to soiling of indoor surfaces.

Indoor Particulate Matter during HOMEChem: Concentrations, Size Distributions, and Exposures.

It is important to improve our understanding of exposure to particulate matter (PM) in residences because of associated health risks. The HOMEChem campaign was conducted to investigate indoor chemistry in a manufactured test house during prescribed everyday activities, such as cooking, cleaning, and opening doors and windows. This paper focuses on measured size distributions of PM (0.001-20 µm), along with estimated exposures and respiratory-tract deposition. Number concentrations were highest for sub-10 nm particles during cooking using a propane-fueled stovetop. During some cooking activities, calculated PM2.5 mass concentrations (assuming a density of 1 g cm-3) exceeded 250 µg m-3, and exposure during the postcooking decay phase exceeded that of the cooking period itself. The modeled PM respiratory deposition for an adult residing in the test house kitchen for 12 h varied from 7 µg on a day with no indoor activities to 68 µg during a simulated day (including breakfast, lunch, and dinner preparation interspersed by cleaning activities) and rose to 149 µg during a simulated Thanksgiving day.

Multiphase Chemistry Controls Inorganic Chlorinated and Nitrogenated Compounds in Indoor Air during Bleach Cleaning.

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.