Indoor Air Quality Through the Lens of Outdoor Atmospheric Chemistry

Outdoor atmospheric chemistry and air quality have been the topic of research that intensified in earnest around the mid-20th century, while indoor air quality research has only been a key focus of chemical researchers over the last 30 years. Examining practices and approaches employed in the outdoor atmospheric chemistry research enterprise provides an additional viewpoint from which we can chart new paths to increase scientific understanding of indoor chemistry. This chapter explores our understanding of primary chemical sources, homogeneous and multiphase reactivity, gas-surface partitioning, and the coupling between the chemistry and dynamics of indoor air through the lens of outdoor atmospheric chemistry. The means to mitigate degraded air quality outdoors are heavily rooted in public policy actions, while the commercial sector mainly promulgates solutions for indoor air quality, making practical and actionable outcomes to research essential for prompt improvements to indoor environments. Indoor and outdoor environments have many important scientific distinctions, but a shared vision for healthy environments motivates both research communities in the same way

A study of the phase transition behavior of mixed ammonium sulfate ? malonic acid aerosols

International audienceThis is a study into the phase transitions of aerosol composed of the ternary system ammonium sulfate (AS) ? malonic acid (MA) ? water using infrared extinction spectroscopy. Twelve compositions were studied in both deliquescence and efflorescence mode experiments. The presence of a MA fraction, by dry mass, (fMA) of 0.1 in an AS aerosol altered the relative humidity at which the phase transitions occur in an atmospherically significant manner. For compositions with 0.25fMAfMA=0.9, the crystallization relative humidity of MA was lowered from RH=6% to less than 1%. Similarly, at fMA=0.4, the AS component did not crystallize. The atmospheric implications of the results are discussed

Chemical evolution of secondary organic aerosol from OH-initiated heterogeneous oxidation

The heterogeneous oxidation of laboratory Secondary Organic Aerosol (SOA) particles by OH radicals was investigated. SOA particles, produced by reaction of α-pinene and O<sub>3</sub>, were exposed to OH radicals in a flow tube, and particle chemical composition, size, and hygroscopicity were measured to assess modifications due to oxidative aging. Aerosol Mass Spectrometer (AMS) mass spectra indicated that the degree of oxidation of 200 nm diameter SOA particles was significantly enhanced due to OH-initiated oxidation, as evidenced by the increase in the fraction of <i>m/z</i> 44 fragment of total organic mass concentration (F44). F44 values of the SOA particles, initially in the range F44=0.04–0.07, increased by up to ΔF44~0.01 under equivalent atmospheric aging timescales of 2 weeks, assuming a 24-h average OH concentration of 10<sup>6</sup> cm<sup>−3</sup>. Particle O/C ratios calculated from F44 values, initially in the range O/C=0.25–0.35, rose by a maximum of ΔO/C~0.04 units for 2 weeks of aging. Particle densities also increased with heterogeneous oxidation, consistent with the observed increase in the degree of oxidation. Minor reductions in particle size, with volume losses of up to 10%, were observed due to volatilization of oxidation products. The SOA particles activated more readily to form cloud droplets with an increase in the κ hygroscopicity parameter of up to a factor of two for the equivalent of 2 weeks of OH atmospheric exposure. These results indicate that OH heterogeneous oxidation of typical SOA needs to be considered as an atmospheric organic aerosol aging mechanism, most likely of higher relative importance away from VOC source regions, where other aging mechanisms are less dominant

A study of the phase transition behavior of internally mixed ammonium sulfate - malonic acid aerosols

International audienceThis is a study into the phase transitions of aerosol composed of the ternary system ammonium sulfate (AS) - malonic acid (MA) - water using infrared extinction spectroscopy. Twelve compositions were studied in both deliquescence and efflorescence mode experiments. The presence of a MA fraction, by dry mass, (fMA) of 0.1 in an AS aerosol altered the relative humidity at which the phase transitions occur in an atmospherically significant manner. For compositions with 0.25fMAfMA=0.9, the crystallization relative humidity of MA was lowered from RH=6% to less than 1%. Similarly, at fMA=0.4, the AS component did not crystallize. The atmospheric implications of the results are discussed

Organic acids as cloud condensation nuclei: Laboratory studies of highly soluble and insoluble species

International audienceThe ability of sub-micron-sized organic acid particles to act as cloud condensation nuclei (CCN) has been examined at room temperature using a newly constructed continuous-flow, thermal-gradient diffusion chamber (TGDC). The organic acids studied were: oxalic, malonic, glutaric, oleic and stearic. The CCN properties of the highly soluble acids - oxalic, malonic and glutaric - match very closely Köhler theory predictions which assume full dissolution of the dry particle and a surface tension of the growing droplet equal to that of water. In particular, for supersaturations between 0.3 and 0.6, agreement between the dry particle diameter which gives 50% activation and that calculated from Köhler theory is to within 3nm on average. In the course of the experiments, considerable instability of glutaric acid particles was observed as a function of time and there is evidence that they fragment to some degree to smaller particles. Stearic acid and oleic acid, which are both highly insoluble in water, did not activate at supersaturations of 0.6% with dry diameters up to 140nm. Finally, to validate the performance of the TGDC, we present results for the activation of ammonium sulfate particles that demonstrate good agreement with Köhler theory if solution non-ideality is considered. Our findings support earlier studies in the literature that showed highly soluble organics to be CCN active but insoluble species to be largely inactive

Ozone decomposition kinetics on alumina: effects of ozone partial pressure, relative humidity and state of film oxidation

International audienceThe room temperature kinetics of gas-phase ozone loss via heterogeneous interactions with thin alumina films has been studied in real-time using 254 nm absorption spectroscopy to monitor ozone concentrations. The films were prepared from dispersions of fine alumina powder in methanol and their surface areas were determined by an in situ procedure using adsorption of krypton at 77 K. The alumina was found to lose reactivity with increasing ozone exposure. However, some of the lost reactivity could be recovered over timescales of days in an environment free of water, ozone and carbon dioxide. From multiple exposures of ozone to the same film it was found that the number of active sites is large, greater than 1.4×1014 active sites per cm2 of surface area, or comparable to the total number of surface sites. The films maintain some reactivity at this point, which is consistent with there being some degree of active site regeneration during the experiment and with ozone loss being catalytic to some degree. The initial uptake coefficients on fresh films were found to be inversely dependent on the starting ozone concentration varying from roughly 10?6 for ozone concentrations of 1014 molecules/cm3 to 10?5 at 1013 molecules/cm3. The initial uptake coefficients were not dependent on the relative humidity, up to 75%, within the precision of the experiment. The reaction mechanism is discussed, as well as the implications these results have for assessing the effect of mineral dust on atmospheric oxidant levels

Ozone decomposition kinetics on alumina: effects of ozone partial pressure, relative humidity and repeated oxidation cycles

International audienceThe room temperature kinetics of gas-phase ozone loss via heterogeneous interactions with thin alumina films has been studied in real-time using 254nm absorption spectroscopy to monitor ozone concentrations. The films were prepared from dispersions of fine alumina powder in methanol and their surface areas were determined by an in situ procedure using adsorption of krypton at 77K. The alumina was found to lose reactivity with increasing ozone exposure. However, some of the lost reactivity could be recovered over timescales of days in an environment free of water, ozone and carbon dioxide. From multiple exposures of ozone to the same film, it was found that the number of active sites is large, greater than 1.4x1014 active sites per cm2 of surface area or comparable to the total number of surface sites. The films maintain some reactivity at this point, which is consistent with there being some degree of active site regeneration during the experiment and with ozone loss being catalytic to some degree. The initial uptake coefficients on fresh films were found to be inversely dependent on the ozone concentration, varying from roughly 10-6 for ozone concentrations of 1014 molecules/cm3 to 10-5 at 1013 molecules/cm3. The initial uptake coefficients were not dependent on the relative humidity, up to 75%, within the precision of the experiment. The reaction mechanism is discussed, as well as the implications these results have for assessing the effect of mineral dust on atmospheric oxidant levels

Fast oxidation of sulfur dioxide by hydrogen peroxide in deliquesced aerosol particles

Atmospheric sulfate aerosols have important impacts on air quality, climate, and human and ecosystem health. However, current air-quality models generally underestimate the rate of conversion of sulfur dioxide (SO2) to sulfate during severe haze pollution events, indicating that our understanding of sulfate formation chemistry is incomplete. This may arise because the air-quality models rely upon kinetics studies of SO2 oxidation conducted in dilute aqueous solutions, and not at the high solute strengths of atmospheric aerosol particles. Here, we utilize an aerosol flow reactor to perform direct investigation on the kinetics of aqueous oxidation of dissolved SO2 by hydrogen peroxide (H2O2) using pH-buffered, submicrometer, deliquesced aerosol particles at relative humidity of 73 to 90%. We find that the high solute strength of the aerosol particles significantly enhances the sulfate formation rate for the H2O2 oxidation pathway compared to the dilute solution. By taking these effects into account, our results indicate that the oxidation of SO2 by H2O2 in the liquid water present in atmospheric aerosol particles can contribute to the missing sulfate source during severe haze episodes