Formation and emission of hydrogen chloride in indoor air

To improve our understanding of chlorine chemistry indoors, reactive chlorine species such as hydrogen chloride (HCl) must be analyzed using fast time-response measurement techniques. Although well studied outdoors, sources of HCl indoors are unknown. In this study, mixing ratios of gaseous HCl were measured at 0.5 Hz in the indoor environment using a cavity ring-down spectroscopy (CRDS) instrument. The CRDS measurement rate provides a major advance in observational capability compared to other established techniques. Measurements of HCl were performed during three types of household activities: (1) floor exposure to bleach, (2) chlorinated and non-chlorinated detergent use in household dishwashers, and (3) cooking events. Surface application of bleach resulted in a reproducible increase of 0.1 ppbv in the affected room. Emissions of HCl from automated dishwashers were observed only when chlorinated detergents were used, with additional HCl emitted during the drying cycle. Increased mixing ratios of HCl were also observed during meal preparation on an electric element stovetop. These observations of HCl derived from household activities indicate either direct emission or secondary production of HCl via chlorine atoms is possible. Calculations of photolysis rate constants of chlorine atom precursors provide evidence that photolysis may contribute to indoor HCl levels

Fine-scale simulation of ammonium and nitrate over the South Coast Air Basin and San Joaquin Valley of California during CalNex-2010

National ambient air quality standards (NAAQS) have been set for PM_2.5 due to its association with adverse health effects. PM_2.5 design values in the South Coast Air Basin (SoCAB) and San Joaquin Valley of California exceed NAAQS levels, and NH^(+)_(4) and NO^(-)_(3) make up the largest fraction of total PM2.5 mass on polluted days. Here we evaluate fine-scale simulations of PM_(2.5) NH^(+)_(4) and NO^(-)_(3) with the Community Multiscale Air Quality model using measurements from routine networks and the California Research at the Nexus of Air Quality and Climate Change 2010 campaign. The model correctly simulates broad spatial patterns of NH^(+)_(4) and NO^(-)_(3) including the elevated concentrations in eastern SoCAB. However, areas for model improvement have been identified. NH_3 emissions from livestock and dairy facilities appear to be too low, while those related to waste disposal in western SoCAB may be too high. Analyses using measurements from flights over SoCAB suggest that problems with NH3 predictions can influence NO^(-)_(3) predictions there. Offline ISORROPIA II calculations suggest that overpredictions of NH_x in Pasadena cause excessive partitioning of total nitrate to the particle phase overnight, while underpredictions of Na^+ cause too much partitioning to the gas phase during the day. Also, the model seems to underestimate mixing during the evening boundary layer transition leading to excessive nitrate formation on some nights. Overall, the analyses demonstrate fine-scale variations in model performance within and across the air basins. Improvements in inventories and spatial allocations of NH_3 emissions and in parameterizations of sea spray emissions, evening mixing processes, and heterogeneous ClNO_2 chemistry could improve model performance

Isocyanic acid in a global chemistry transport model:tropospheric distribution, budget, and identification of regions with potential health impacts

This study uses a global chemical transport model to estimate the distribution of isocyanic acid (HNCO). HNCO is toxic, and concentrations exceeding 1 ppbv have been suggested to have negative health effects. Based on fire studies, HNCO emissions were scaled to those of hydrogen cyanide (30%), resulting in yearly total emissions of 1.5 Tg for 2008, from both anthropogenic and biomass burning sources. Loss processes included heterogeneous uptake (pH dependent), dry deposition (like formic acid), and reaction with the OH radical (k = 1 × 10−15 molecule−1 cm3 s−1). Annual mean surface HNCO concentrations were highest over parts of China (maximum of 470 pptv), but episodic fire emissions gave much higher levels, exceeding 4 ppbv in tropical Africa and the Amazon, and exceeding 10 ppbv in Southeast Asia and Siberia. This suggests that large biomass burning events could result in deleterious health effects for populations in these regions. For the tropospheric budget, using the model-calculated pH the HNCO lifetime was 37 days, with the split between dry deposition and heterogeneous loss being 95%:5%. Fixing the heterogeneous loss rate at pH = 7 meant that this process dominated, accounting for ∼70% of the total loss, giving a lifetime of 6 days, and resulting in upper tropospheric concentrations that were essentially zero. However, changing the pH does not notably impact the high concentrations found in biomass burning regions. More observational data is needed to evaluate the model, as well as a better representation of the likely underestimated biofuel emissions, which could mean more populations exposed to elevated HNCO concentrations

Composition of size-resolved aged boreal fire aerosols: Brown carbon, biomass burning tracers, and reduced nitrogen

Aerosols that were size-resolved into 13 fractions between 10 nm and 18 μm were collected from an aged boreal forest wildfire plume in July 2013. Samples were extracted into water and analyzed for molecular-size-resolved brown carbon (BrC), biomass burning (BB) markers, reduced nitrogen compounds, and elemental composition. Absorption of BrC was primarily in fine-mode aerosols and dominated by high-molecular-weight compounds (>500 Da). The molecular size distribution of BrC was conserved across aerosol sizes, with a decrease in the importance of large molecules in smaller aerosols. The aerosol-size-resolved composition of BrC absorption was different than those of the two BB markers, non-sea-salt potassium and levoglucosan, suggesting that they may not be suitable for identifying BB BrC in aged plumes. Strong correlations were observed between BrC and the reduced nitrogen compounds ammonium, dimethylamine, and diethylamine. In aerosols with high BrC and reduced nitrogen, there was a strong cationic excess. These observations could be caused by (i) uptake of ammonium and alkylamines to form stable salts with organic acids or (ii) reactive uptake to form imines or enamines that were hydrolyzed during the BrC extraction process.Funding was provided by the Natural Sciences and Engineering Research Council of Canada through Discovery and Research, Tools, and Infrastructure Grants. T.C.V. acknowledges a Banting Postdoctoral Fellowship

Non-Woven Materials for Cloth-Based Face Mask Inserts: Relationship Between Material Properties and Sub-Micron Aerosol Filtration

Current guidance by leading public health agencies recommends wearing a 3-layer cloth-based face mask with a middle non-woven material insert to reduce the transmission of infectious respiratory viruses like SARS-CoV-2. In this work we explore the material characteristics for a range of readily available non-woven materials and their sub-micron particle filtration efficiency (PFE), with the aim of providing evidence-based guidelines for selecting appropriate materials as inserts in cloth-based masks. We observed a wide range of ideal PFE for the tested non-woven materials, with polypropylene, Swiffer and Rayon/polyester blend providing the highest PFE and breathability. Our results suggest that materials comprising loose 3D fibrous webs (e.g. flannel, Swiffer and gauze) exhibited enhanced filtration efficiency compared to compressed counterparts. Common modifications to fabrics, such as water-resistant treatment and a sewn seam were also investigated. Overall, we demonstrate that adding an appropriate non-woven material as an insert filter can significantly improve the performance of cloth-based masks, and there exist suitable cellulose-based alternatives to polypropylene.</div

Composition of Size-Resolved Aged Boreal Fire Aerosols: Brown Carbon, Biomass Burning Tracers, and Reduced Nitrogen

Aerosols that were size-resolved into 13 fractions between 10 nm and 18 μm were collected from an aged boreal forest wildfire plume in July 2013. Samples were extracted into water and analyzed for molecular-size-resolved brown carbon (BrC), biomass burning (BB) markers, reduced nitrogen compounds, and elemental composition. Absorption of BrC was primarily in fine-mode aerosols and dominated by high-molecular-weight compounds (>500 Da). The molecular size distribution of BrC was conserved across aerosol sizes, with a decrease in the importance of large molecules in smaller aerosols. The aerosol-size-resolved composition of BrC absorption was different than those of the two BB markers, non-sea-salt potassium and levoglucosan, suggesting that they may not be suitable for identifying BB BrC in aged plumes. Strong correlations were observed between BrC and the reduced nitrogen compounds ammonium, dimethylamine, and diethylamine. In aerosols with high BrC and reduced nitrogen, there was a strong cationic excess. These observations could be caused by (i) uptake of ammonium and alkylamines to form stable salts with organic acids or (ii) reactive uptake to form imines or enamines that were hydrolyzed during the BrC extraction process

Time-Resolved Measurements of Nitric Oxide, Nitrogen Dioxide, and Nitrous Acid in an Occupied New York Home

Indoor oxidizing capacity in occupied residences is poorly understood. We made simultaneous continuous time-resolved measurements of ozone (O₃), nitric oxide (NO), nitrogen dioxide (NO₂), and nitrous acid (HONO) for two months in an occupied detached home with gas appliances in Syracuse, NY. Indoor NO and HONO mixing ratios were higher than those outdoors, whereas O₃ was much lower (sub-ppbv) indoors. Cooking led to peak NO, NO₂, and HONO levels 20–100 times greater than background levels; HONO mixing ratios of up to 50 ppbv were measured. Our results suggest that many reported NO₂ levels may have a large positive bias due to HONO interference. Nitrous acid, NO₂, and NO were removed from indoor air more rapidly than CO₂, indicative of reactive removal processes or surface uptake. We measured spectral irradiance from sunlight entering the residence through glass doors; hydroxyl radical (OH) production rates of (0.8–10) × 10⁷ molecules cm^–3 s^–1 were calculated in sunlit areas due to HONO photolysis, in some cases exceeding rates expected from ozone–alkene reactions. Steady-state nitrate radical (NO₃) mixing ratios indoors were predicted to be lower than 1.65 × 10⁴ molecules cm^–3. This work will help constrain the temporal nature of oxidant concentrations in occupied residences and will improve indoor chemistry models