Knowledge gaps related to mass transfer processes involved in passive air sampling of semivolatile organic compounds and factors potentially influencing passive sampling rates (PSRs) were addressed with controlled laboratory experiments, mass transfer modeling, and a field sampling campaign. The observed non-uniform SVOC distributions within porous passive sampling media (PSMs) contradict an assumption in an earlier passive air sampling theory and proved the existence of a kinetic resistance on the PSM side. This resistance can affect PSRs as revealed by a new PAS model which is based on fundamental laws of mass transfer in air and porous media. By considering mass transfer processes within the PSM, the model is able to explain the large variations of field calibrated PSRs with temperature and between SVOC species and the two-stage uptake process, which cannot be addressed by the earlier PAS theory. Because the PSM side kinetic resistance invalidates the assumption that depuration compounds added to the PSM prior to deployment are subject to the same kinetic resistance as the sampled SVOCs, PSRs derived from the loss rates of depuration compounds can differ from the actual PSRs of the sampled SVOCs. Using such PSRs could thus introduce additional uncertainty to PAS-derived air concentrations. Experiments using XAD-resin and silica-gel filled mesh cylinder as PSMs for the uptake of SVOCs and water vapor respectively revealed that sorbent in the inner portion of the PSM does not take part in chemical uptake; PSRs are thus proportional to the interfacial transfer area but not the amount of the sorbent. Accordingly, thinner PSM can be used to reduce the amount of sorbent while keeping or even increasing the PSRs. Optimized designs of PASs could be tested time efficiently using the gravimetrical approach based on water vapor uptake by silica gel.

Knowledge gaps related to mass transfer processes involved in passive air sampling of semivolatile organic compounds and factors potentially influencing passive sampling rates (PSRs) were addressed with controlled laboratory experiments, mass transfer modeling, and a field sampling campaign. The observed non-uniform SVOC distributions within porous passive sampling media (PSMs) contradict an assumption in an earlier passive air sampling theory and proved the existence of a kinetic resistance on the PSM side. This resistance can affect PSRs as revealed by a new PAS model which is based on fundamental laws of mass transfer in air and porous media. By considering mass transfer processes within the PSM, the model is able to explain the large variations of field calibrated PSRs with temperature and between SVOC species and the two-stage uptake process, which cannot be addressed by the earlier PAS theory. Because the PSM side kinetic resistance invalidates the assumption that depuration compounds added to the PSM prior to deployment are subject to the same kinetic resistance as the sampled SVOCs, PSRs derived from the loss rates of depuration compounds can differ from the actual PSRs of the sampled SVOCs. Using such PSRs could thus introduce additional uncertainty to PAS-derived air concentrations. Experiments using XAD-resin and silica-gel filled mesh cylinder as PSMs for the uptake of SVOCs and water vapor respectively revealed that sorbent in the inner portion of the PSM does not take part in chemical uptake; PSRs are thus proportional to the interfacial transfer area but not the amount of the sorbent. Accordingly, thinner PSM can be used to reduce the amount of sorbent while keeping or even increasing the PSRs. Optimized designs of PASs could be tested time efficiently using the gravimetrical approach based on water vapor uptake by silica gel.

Although the air-ice interface is atmospherically important, it is difficult to model accurately because exclusion and precipitation of solutes during freezing, deposition of atmospheric species, and heterogeneous/photochemical processes all affect its properties. In this thesis, glancing-angle spectroscopic methods were developed to study ice surfaces. Glancing-angle Raman spectroscopy showed that nitrate is not strongly excluded to the ice surface during freezing, in contradiction with expectations based on equilibrium thermodynamics. Glancing-angle laser-induced fluorescence showed that hydronium ions are not strongly excluded when dilute acidic solutions (HNO3 or HCl) are frozen. These results suggest that solutes are not universally excluded and that care should be taken in modelling surface concentrations on ice. Deposition of HCl(g) was found to result in different pH responses at the "pure" vs. "salty" ice surfaces. Changes at the "salty" ice surface were consistent with the existence of a brine layer at the air-ice interface while changes at the "pure" ice surface were distinctly different, indicating that it may not be appropriate to model it as a cold, liquid layer. Significantly, results also suggest that the sea ice surface is buffered against pH changes, with important implications for interpreting pH-dependent chemistry. The conversion of sea-salt derived halides to reactive halogen species can lead to dramatic changes in the oxidative capacity of the overlying atmosphere. At ambient pH and naturally occurring halide concentrations, the dark ozonation of NaBr and NaI solutions was found to proceed more quickly on frozen vs. aqueous substrates, consistent with a freeze-concentration enhancement in halide concentration at the surface. A photochemical mechanism for halogen release from artificial saline snow was evidenced. The presence of ozone and light in the actinic region leads to accelerated production of Br2 and BrCl and the release of Cl2, in a process enhanced by high surface area, acidity and additional gas phase Br2. The results provide strong evidence for snowpack "halogen explosion" chemistry in which gas phase halogens are recycled back into a concentrated brine layer at the snow grain surface.

Although the air-ice interface is atmospherically important, it is difficult to model accurately because exclusion and precipitation of solutes during freezing, deposition of atmospheric species, and heterogeneous/photochemical processes all affect its properties. In this thesis, glancing-angle spectroscopic methods were developed to study ice surfaces. Glancing-angle Raman spectroscopy showed that nitrate is not strongly excluded to the ice surface during freezing, in contradiction with expectations based on equilibrium thermodynamics. Glancing-angle laser-induced fluorescence showed that hydronium ions are not strongly excluded when dilute acidic solutions (HNO3 or HCl) are frozen. These results suggest that solutes are not universally excluded and that care should be taken in modelling surface concentrations on ice. Deposition of HCl(g) was found to result in different pH responses at the "pure" vs. "salty" ice surfaces. Changes at the "salty" ice surface were consistent with the existence of a brine layer at the air-ice interface while changes at the "pure" ice surface were distinctly different, indicating that it may not be appropriate to model it as a cold, liquid layer. Significantly, results also suggest that the sea ice surface is buffered against pH changes, with important implications for interpreting pH-dependent chemistry. The conversion of sea-salt derived halides to reactive halogen species can lead to dramatic changes in the oxidative capacity of the overlying atmosphere. At ambient pH and naturally occurring halide concentrations, the dark ozonation of NaBr and NaI solutions was found to proceed more quickly on frozen vs. aqueous substrates, consistent with a freeze-concentration enhancement in halide concentration at the surface. A photochemical mechanism for halogen release from artificial saline snow was evidenced. The presence of ozone and light in the actinic region leads to accelerated production of Br2 and BrCl and the release of Cl2, in a process enhanced by high surface area, acidity and additional gas phase Br2. The results provide strong evidence for snowpack "halogen explosion" chemistry in which gas phase halogens are recycled back into a concentrated brine layer at the snow grain surface.

This study describes two projects involving recent research on atmospheric ammonia. The first project investigates differences in modelling techniques of aerosol acidity using data from two recent field campaigns. Our results show that allowing or disallowing gas-particle partitioning in the Extended Aerosol Inorganic Model (E-AIM) changed the average modelled aerosol activity of H+ from one campaign by seven orders of magnitude and that disallowing gas-particle partitioning may not accurately represent the chemical state of the aerosols. The second project investigates the interference of reduced nitrogen in commercial chemiluminescent nitrogen oxide monitors with molybdenum oxide catalytic converters. This phenomenon is strongly dependent on the temperature of the catalytic converter. Our results show these instruments can have high conversion efficiencies of gaseous NH3 and NH4+ salts to NO at typical reported converter temperatures, but conversion efficiency varies between instruments and may be the result of uncertainty in reported converter temperature.

The role of weather and climate variability on the health of Aboriginal people in Fort Albany and Toronto, Ontario, Canada is explored through four complementary research studies. The first study examined past temperature trends of Fort Albany (using climate records of Moosonee) and Toronto. Temperature variability was found to be greater in Moosonee than in Toronto, and day to day temperature minimum (Tmin) threshold exceedances of 5 degrees Celsius was found to have significantly declined in both Toronto and Fort Albany. The second study explored the effects of climate change on a rural First Nation group in Fort Albany. Observed environmental changes include changes in the timing of seasons, spring melt and ice freeze-up; warmer seasons, an increase in extreme and unpredictable weather, and changes in animal patterns. These changes have affected subsistence harvesting activities and community infrastructure, which have lead to increased health risks, though many community members have exhibited resiliency and adaptation. The third study compared current health status between an urban Aboriginal and non-Aboriginal group. Urban Aboriginal participants were found to be at greater risk to psychological distress and seasonal affective disorder (SAD) than non-Aboriginal participants. Moreover, those who self-rated their health as poor/fair were more likely to exhibit psychological distress than those who self-rated their health as good/very good/excellent. The fourth study compared the effects of weather and seasonal change among a rural First Nation group, an urban Aboriginal group and an urban non-Aboriginal group. Urban Aboriginal participants were most affected by weather while rural Aboriginal (i.e. First Nation) participants were least affected by weather. These studies demonstrate that both urban and rural Aboriginal groups may be at risk to climate change and weather-related changes; though specific implications may differ due to different lifestyles and capacities to adapt to environmental conditions.

Atmospheric inversion has recently become an important tool in estimating CO2 sinks and sources albeit that the existing inversion results are often uncertain and differ considerably in terms of the spatiotemporal variations of the inverted carbon flux. More measurements combined with terrestrial ecosystem information are expected to improve the estimates of global surface carbon fluxes which are used to understand the relationships between variabilities of the terrestrial carbon cycle and anomalies of climatic factors. Inversions using more observations have often been hampered by the intense diurnal variations of CO2 concentrations at continental sites. Diurnal variations of the surface flux are included with atmospheric boundary dynamics in order to improve the atmospheric inversion accuracy. Modeling experiments conducted in this study show that inverse estimates of the carbon flux are more sensitive to the variation of the atmospheric boundary layer dynamics than to the diurnal variation in the surface flux. It is however generally better to consider both diurnal variations in the inversion than to consider only either of them. Forest carbon dynamics is closely related to stand age. This useful terrestrial ecosystem information has been used as an additional constraint to the atmospheric inversion. The inverse estimates with this constraint over North America exhibit an improved correlation with carbon sink estimates derived from eddy-covariance measurements and remotely-sensed data, indicating that the use of age information can improve the accuracy of atmospheric inversions. Terrestrial carbon uptake is found mainly in northern land, and a strong flux density is revealed in southeastern North America in an improved multi-year inversion from 2002 to 2007. The global interannual variability of the flux is dominated by terrestrial ecosystems. The interannual variabilities of regional terrestrial carbon cycles could be mostly explained by monthly anomalies of climatic conditions or short-time extreme meteorological events. Monthly anomalies of the inverted fluxes have been further analyzed against the monthly anomalies of temperature and precipitation to quantitatively assess the responses of the global terrestrial carbon cycle to climatic variabilities and to determine the dominant mechanisms controlling the variations of terrestrial carbon exchange.

Atmospheric particles can affect climate directly, by scattering solar radiation, or indirectly, by acting as the seed upon which cloud droplets form. These clouds can then cool the earth's surface by reflecting incoming sunlight. In order to constrain the large uncertainties in predicting the ultimate effect of aerosol on climate, the sources of atmospheric particles and their subsequent ability to turn into cloud droplets needs to be better understood. This thesis addresses two parts of this issue: the sources of Arctic aerosol and the hygroscopicity of continental organic aerosol. Small particles were observed in Baffin Bay during September 2008 that coincided with high atmospheric and ocean surface dimethyl sulphide (DMS) concentrations suggesting that the aerosol formed from oceanic sources. An aerosol microphysics box model confirmed that local DMS could have produced the observed particles. In addition, the particle chemical composition was measured using aerosol mass spectrometry in the central Arctic Ocean in August 2008 and particles were found to be 43% organic and 46% sulphate. Factor analysis further apportioned the aerosol mass to marine biogenic and continental sources 33% and 36% of the time, respectively, with the source of the remaining mass unidentified. The second part of the study parameterises the hygroscopicity of the ambient organic aerosol fraction (κorg) at Egbert, Ontario and Whistler, British Columbia. This was done using two methods: 1) by assuming that the oxygenated organic component was hygroscopic and that the unoxygenated organic component was non-hygroscopic, κ of the oxygenated component was found to be 0.22 ± 0.04, and 2) by assuming that κorg varied linearly with the atomic oxygen to atomic carbon ratio, it could be parameterised as κorg = (0.29 ± 0.05) × (O/C). Calculations predict that knowing κorg is important in urban, semi-urban, and remote locations whenever the inorganic mass fraction is low.

Open and throughfall precipitation samples were collected at Haliburton Forest for a total of nine events from July – November of 2009. The following species were analyzed quantitatively: NO3-, SO42-, Cl-, HCOO-, C2O42-, NH4+, Na+, K+, Ca2+, and Mg2+. Wet deposition inputs to the system were quantified and the sources of wet-deposited species were probed. The throughfall method was employed to quantify inputs to the forest floor and probe canopy-precipitation interactions. Leaf wash samples at three heights aided in the interpretation of throughfall data and allowed for an examination of vertical profiles of dry deposition to the canopy. Results suggest possible nitrate foliar leaching during the growing season, although this appears to cease during senescence. This finding supports previous evidence that Haliburton Forest has shifted from nitrogen-limitation toward nitrogen-saturation and estimated total atmospheric N inputs to the system are close to the proposed critical load of 10 kg N ha-1 yr-1.

Fluorinated compounds are environmentally persistent and have been demonstrated to bioaccumulate and contribute to climate change. The focus of this work was to better understand the atmospheric chemistry of poly- and per-fluorinated compounds in order to appreciate their impacts on the environment. Several fluorinated compounds exist for which data on climate impacts do not exist. Radiative efficiencies (REs) and atmospheric lifetimes of two new long-lived greenhouse gases (LLGHGs) were determined using smog chamber techniques: perfluoropolyethers and perfluoroalkyl amines. Through this, it was observed that RE was not directly related to the number of carbon-fluorine bonds. A structure-activity relationship was created to allow the determination of RE solely from the chemical structure of the compound. Also, a novel method was developed to detect polyfluorinated LLGHGs in the atmosphere. Using carbotrap, thermal desorption and cryogenic extraction coupled to GC-MS, atmospheric measurements can be made for a number of previously undetected compounds. A perfluoroalkyl amine was detected in the atmosphere using this technique, which is the compound with the highest RE ever detected in the atmosphere. Perfluorocarboxylic acids (PFCAs) are water soluble and non-volatile, suggesting they are not susceptible to long-range transport. A hypothesis was derived to explain the ubiquitous distribution of these compounds involving atmospheric formation of PFCAs from volatile precursors. Using smog chamber techniques with offline analysis, perfluorobutenes and fluorotelomer iodides were shown to yield PFCAs from atmospheric oxidation. Dehydrofluorination of perfluorinated alcohols (PFOHs) is poorly understood in the mechanism of PFCA atmospheric formation. Using density functional techniques, overtone-induced photolysis was shown to lead to dehydrofluorination of PFOHs. In the presence of water, this mechanism could be a sink of PFOHs in the atmosphere. Confirmation of the importance of volatile precursors was derived from examination of snow from High Arctic ice caps. This provided the first empirical evidence of atmospheric deposition. Through the analytes observed, fluxes and temporal trends, it was concluded that atmospheric oxidation of volatile precursors is an important source of PFCAs to the Arctic.