Using a coated-wall flow tube connected to a mass spectrometer, the heterogeneous conversion of NO2 to HONO on dry hydrocarbon soot surfaces has been studied at room temperature and 243 K. Particular attention was given to the measurement of the HONO yield as a function of hydrocarbon fuel, NO2 partial pressure, extent of uptake, and surface oxidation state. In all cases, the yield is invariant of these parameters and close to unity, indicative of an irreversible oxidation mechanism by which the NO2 abstracts an H atom from the surface. XPS analysis shows that the surface N content does not measurably increase with NO2 exposure. There is minimal surface reactivity regeneration with time or via exposure to high relative humidity. A BET surface area measurement of the entire soot film exposed to NO2 was used to determine the amount of HONO that can be generated from the soot surface per unit surface area, prior to its deactivation. The reduction of NO2 to HONO on soot is unlikely to account for the observed nighttime buildup of HONO in polluted urban environments.

The adsorption of gas-phase nitric acid on n-hexane soot was measured as a function of temperature, relative humidity (RH), and nitric acid partial pressure in a coated-wall flow tube coupled to an electron-impact mass spectrometer. The specific surface area (SSA) of the soot, determined from the BET isotherm of Kr at 77 K for each sample, was 88-372 times larger than the geometric surface area. The SSA increased linearly with soot mass for thin samples but saturated at high mass. For the most part, the nitric acid adsorption was reversible in the submonolayer regime, and no indication of HONO formation was observed. The uptake increased with decreasing temperature and, for surface coverages between 10 12 and 10 13 molecules cm -2 , the average enthalpy of adsorption was -55.8 ( 7.7 kJ mol -1 . A Langmuir-Freundlich model with the heterogeneity parameter equal to 0.5 closely describes the uptake data, implying either that the surface sites are energetically heterogeneous or that nitric acid is dissociating on the surface. The nitric acid adsorption isotherms were independent of relative humidity up to 80% RH at 243 K. Exposure to ppm levels of ozone for about 1 h had no effect on the adsorption. The atmospheric implications of this work are discussed.

The adsorption isotherms of a series of aromatic hydrocarbons on n-hexane soot were measured as a function of temperature and partial pressure in a coated-wall flow tube coupled to an electron-impact mass spectrometer. The specific surface area was determined for each of the samples by measuring the BET isotherm of Kr at 77 K. The gas-to-surface uptakes were fully reversible with the extent of adsorption increasing with decreasing temperature and increasing partial pressures. At low partial pressures, the isotherms were well modeled by the Langmuir isotherm for all experimental conditions, and the adsorption was found to saturate at one monolayer of coverage at approximately 2 x 10(14) molecule cm(-2). For the less volatile species, evidence for multilayer adsorption was observed and the BET isotherm was used instead. The experimental enthalpies of adsorption were consistently higher than the enthalpies of vaporization for all compounds. A linear free-energy relationship was developed between the Langmuir equilibrium constant for adsorption and the compound's (sub-cooled) liquid vapor pressure, providing validation for the use of such relationships in assessing gas-particle partitioning of aromatic hydrocarbons to soot aerosols in the environment. The experimental results were compared to the Junge-Pankow gas-to-aerosol partitioning model.

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Previous research has shown that indoor benzene levels in homes with attached garages are higher than homes without attached garages. Exhaust ventilation in attached garages is one possible intervention to reduce these concentrations. To evaluate the effectiveness of this intervention, a randomized crossover study was conducted in 33 Ottawa homes in winter 2014. VOCs including benzene, toluene, ethylbenzene, and xylenes, nitrogen dioxide, carbon monoxide, and air exchange rates were measured over four 48-hour periods when a garage exhaust fan was turned on or off. A blower door test conducted in each garage was used to determine the required exhaust fan flow rate to provide a depressuri- | INTRODUCTIONRecent Canadian studies have shown that non-smoking, single-family homes with attached garages have higher indoor levels of certain air pollutants, including benzene, compared to homes without. 1-4In these studies, homes with attached garages had indoor benzene concentrations that were 2.4-2.9 times higher than homes without attached garages, after adjusting for other factors. This is of concern given that approximately 61% of all Canadian dwellings have an attached garage 5 and that benzene is a known carcinogen. that residential benzene levels be reduced as much as possible to minimize exposures. 9-11A 2014 unpublished Health Canada survey of products and equipment found in attached garages conducted across nine Canadian metropolitan areas found that homeowners generally use their garage to park vehicles and store material (e.g., fuels, automotive products, gaspowered equipment, and solvents). It has previously been shown that gasoline-powered vehicles and equipment, as well as some material † Both authors contributed equally to this work and are considered to be first author.Reproduced with the permission of the Minister of Health Canada. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Indoor air quality is a major issue for public health, particularly in northern communities. In this extreme environment, adequate ventilation is crucial to provide a healthier indoor environment, especially in airtight dwellings. The main objective of the study is to assess the impact of ventilation systems and their optimization on microbial communities in bioaerosols and dust in 54 dwellings in Nunavik. Dwellings with three ventilation strategies (without mechanical ventilators, with heat recovery ventilators, and with energy recovery ventilators) were investigated before and after optimization of the ventilation systems. Indoor environmental conditions (temperature, relative humidity) and microbiological parameters (total bacteria, Aspergillus/Penicillium, endotoxin, and microbial biodiversity) were measured. Dust samples were collected in closed face cassettes with a polycarbonate filter using a micro‐vacuum while a volume of 20 m3 of bioaerosols were collected on filters using a SASS3100 (airflow of 300 L/min). In bioaerosols, the median number of copies was 4.01 × 103 copies/m3 of air for total bacteria and 1.45 × 101 copies/m3 for Aspergillus/Penicillium. Median concentrations were 5.13 × 104 copies/mg of dust, 5.07 × 101 copies/mg, 9.98 EU/mg for total bacteria, Aspergillus/Penicillium and endotoxin concentrations, respectively. The main microorganisms were associated with human occupancy such as skin‐related bacteria or yeasts, regardless of the type of ventilation.

Cooking is the main source of ultrafine particles (UFP) in homes. This study investigated the effect of venting range hood flow rate on size-resolved UFP concentrations from gas stove cooking. The same cooking protocol was conducted 60 times using three venting range hoods operated at six flow rates in twin research houses. Size-resolved particle (10-420 nm) concentrations were monitored using a NanoScan scanning mobility particle sizer (SMPS) from 15 min before cooking to 3 h after the cooking had stopped. Cooking increased the background total UFP number concentrations to 1.3 Â 10 3 particles/cm 3 on average, with a mean exposure-relevant source strength of 1.8 Â 10 12 particles/min. Total particle peak reductions ranged from 25% at the lowest fan flow rate of 36 L/s to 98% at the highest rate of 146 L/s. During the operation of a venting range hood, particle removal by deposition was less significant compared to the increasing air exchange rate driven by exhaust ventilation. Exposure to total particles due to cooking varied from 0.9 to 5.8 Â 10 4 particles/cm 3 Áh, 3 h after cooking ended. Compared to the 36 L/s range hood, higher flow rates of 120 and 146 L/s reduced the first-hour post-cooking exposure by 76% and 85%, respectively.