Atmospheric ammonia contributes to a number of environmental problems, but many questions regarding the behaviour of ammonia in the atmosphere remain. Field studies were performed to investigate the gas-particle partitioning of ammonia, the surface-atmosphere exchange, and to compare measurements with an online chemical transport model and offline thermodynamic models. A state-of-the-art instrument, Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS), with a novel sampling technique was used to measure ammonia. The detection limit of the instrument was found to be 690 ppt at 1 Hz and 42 ppt when averaged to 5 minutes. The uncertainty in the measurement is 10 % based on calibration from a permeation tube source. Laboratory and field tests show the ammonia time response to be slower at lower mixing ratios, and when the ambient relative humidity is high. Observations from the first field campaign discussed, the Border Air Quality and Meteorology Study (BAQS-Met), were compared to a chemical transport model AURAMS (A Unified Regional Air quality Modeling System). The model was often biased low in ammonia and ammonium and predicted an incorrect diurnal profile. Observations suggest a coupling between gas-particle and surface-atmosphere equilibria whereby a large atmospheric condensation sink induces emission of ammonia from the surface. A simple approach at representing the ammonia bi-direction flux more closely matched the observations, indicating that a fully coupled bi-directional flux parameterization in chemical transport models is necessary to accurately predict atmospheric ammonia. A suite of instrumentation during the CalNex 2010 field campaign allowed for in-depth analysis of gas-particle partitioning and estimation of aerosol pH. Observations were compared to predictions from the thermodynamic equilibrium models ISORROPIA and E-AIM. Deviations form equilibrium were found during periods of high levels of aerosol nitrate and positive net charge. The gas-particle partitioning was found to be very sensitive to aerosol pH.

Atmospheric ammonia contributes to a number of environmental problems, but many questions regarding the behaviour of ammonia in the atmosphere remain. Field studies were performed to investigate the gas-particle partitioning of ammonia, the surface-atmosphere exchange, and to compare measurements with an online chemical transport model and offline thermodynamic models. A state-of-the-art instrument, Quantum Cascade Tunable Infrared Laser Differential Absorption Spectrometer (QC-TILDAS), with a novel sampling technique was used to measure ammonia. The detection limit of the instrument was found to be 690 ppt at 1 Hz and 42 ppt when averaged to 5 minutes. The uncertainty in the measurement is 10 % based on calibration from a permeation tube source. Laboratory and field tests show the ammonia time response to be slower at lower mixing ratios, and when the ambient relative humidity is high. Observations from the first field campaign discussed, the Border Air Quality and Meteorology Study (BAQS-Met), were compared to a chemical transport model AURAMS (A Unified Regional Air quality Modeling System). The model was often biased low in ammonia and ammonium and predicted an incorrect diurnal profile. Observations suggest a coupling between gas-particle and surface-atmosphere equilibria whereby a large atmospheric condensation sink induces emission of ammonia from the surface. A simple approach at representing the ammonia bi-direction flux more closely matched the observations, indicating that a fully coupled bi-directional flux parameterization in chemical transport models is necessary to accurately predict atmospheric ammonia. A suite of instrumentation during the CalNex 2010 field campaign allowed for in-depth analysis of gas-particle partitioning and estimation of aerosol pH. Observations were compared to predictions from the thermodynamic equilibrium models ISORROPIA and E-AIM. Deviations form equilibrium were found during periods of high levels of aerosol nitrate and positive net charge. The gas-particle partitioning was found to be very sensitive to aerosol pH.

The characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and the variation of the gas-particle partitioning of PCDD/Fs near two municipal solid waste incinerators (MSWIs) located in southern Taiwan were investigated. In order to better understand the mechanism of dry deposition, the atmospheric dry deposition flux and velocity of PCDD/Fs were calculated. It was found that the mean atmospheric PCDD/F concentrations (0.0348-0.106 pg I-TEQ/Nm3) were comparable to those detected in the vicinity of MSWIs in Taiwan, but significantly lower than those in a highly industrialized urban area (0.150 pg I-TEQ/Nm3) located in southern Taiwan. The relatively higher atmospheric PCDD/F concentrations was found in winter than in summer. The calculated total dry deposition flux of PCDD/Fs ranged from 0.0274-0.718 ng I-TEQ/m2-month, and the atmospheric deposition flux in winter tended to be higher than those in summer. The results also indicated that dry deposition velocities of atmospheric particles for each month ranged from 0.52-0.91 cm/s (mean = 0.63 cm/s) and 0.48-0.73 cm/s (mean = 0.55 cm/s) in sites A and B, respectively, which were similar to that for the ambient air near two MSWIs in Taiwan, but slightly higher than those in urban area of Korea. In addition, the dry deposition of PCDD/Fs was mainly contributed by particle-phase at both sampling areas during the estimated period. The above results demonstrated that the dominant mechanism of dry deposition was particle phase deposition. The annual variations of wet deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in atmosphere were also measured at two sites (A and B). Results showed that particle scavenging dominates in the wet deposition processes for the removal of PCDD/Fs from the atmosphere, the highest value was observed at the highest chlorinated congener. The ambient temperature and the amount of precipitation played an important role in the variation of PCDD/F deposition fluxes. It was found that temperature was inversely associated with the existence of particulate PCDD/Fs, indicating PCDD/Fs are scavenged most efficiently in cold weather. PCDD/F wet deposition fluxes in rainy seasons (from June to August) were significantly higher than those in dry seasons (from December to February), revealing a positive relationship between wet deposition flux and monthly rainfall. Additionally, the annual total (dry + wet) deposition fluxes of PCDD/Fs were 149 ng/m2-year (5.02 ng I-TEQ/m2-year) and 177 ng/m2-year (5.11 ng I-TEQ/m2-year) for sites A and B, respectively, revealing that dry deposition was more dominant than the wet deposition for the atmospheric deposition of PCDD/Fs. Since atmospheric deposition is believed to be the main transfer pathway of PCDD/Fs into food chains, its impact on human exposure to PCDD/Fs is of great importance.

Mercury (Hg) is a potent neurotoxin, has both natural and anthropogenic sources to the environment, and is globally dispersed. Humans have been using Hg since antiquity and continue its use in large quantities, mobilizing Hg from stable long-lived geologic reservoirs to actively cycling surface terrestrial and aquatic ecosystems. Human activities, such as mining and coal combustion, have perturbed the natural biogeochemical cycle of Hg. However, the distribution of natural versus anthropogenic Hg in the environment today and the extent of anthropogenic perturbation (i.e., enrichment) are uncertain. Previous model estimates of anthropogenic enrichment have been limited by a lack of information about historical emissions, examined only near-term effects, or have not accounted for the full coupling between biogeochemical reservoirs. Presented here is a framework that integrates recently available historical emission inventories and overcomes these barriers, providing an improved quantitative understanding of global Hg cycling. / Earth and Planetary Sciences

Perfluoroalkyl acids (PFAAs) are man-made chemicals which have been observed in the global environment, even in locations far away from where they are emitted. These persistent substances are taken up in humans and biota and may have toxic effects. Knowledge about how PFAAs are dispersed in the environment is needed to discern strategies to manage their sources and to evaluate the efficacy of adopted legislation. This thesis aimed to increase our understanding of the sources of PFAAs to the atmosphere and how PFAAs are transported in air. The results of Paper I demonstrated that gaseous perfluorooctanoic acid (PFOA) sorbs to typical glass fibre filters (GFFs) used in high-volume air sampling of PFAAs. As a consequence, the fraction of gaseous PFOA present in sampled air is underestimated, while the fraction of PFOA associated with aerosols is overestimated. Replacing GFFs with filters deactivated through silanisation and siliconisation did not eliminate this sampling artefact and is therefore not recommended as a means to determine the gas-particle partitioning of PFAAs. In Paper II, monitoring of the mass of PFOA transferred from water solutions of pH 0.2-5.5 demonstrated that the acid dissociation constant of linear PFOA and the four most ubiquitous branched PFOA isomers is around or below 1. Furthermore, the results demonstrated that the presence of counter ions and organic matter in water retarded, rather than enhanced, the volatilisation of PFOA. Therefore, volatilisation of all isomers of PFOA from environmental waters is expected to be negligible. To further study the transfer of PFAAs from environmental waters to air, Paper III simulated the process of sea spray generation in the laboratory. Strong enrichment of PFAAs was observed from bulk water to the surface microlayer and to aerosols. The enrichment increased with PFAA chain length, indicating that this process is of greater importance for more surface active substances. The highest enrichment was observed in aerosols &lt; 1.6 µm, which can travel over long distances if not rained out. Based on the measured aerosol enrichment factors we estimated that approximately 70 metric tonnes of PFAAs are aerosolised from the global oceans yearly and that 3% of this mass is deposited in terrestrial environments. Paper IV reported the occurrence of branched PFOA isomers in deposition sampled in five geographical locations. The presence of these isomers demonstrated that atmospheric transformation of fluorotelomer alcohols is not the only ongoing source of PFAAs to air. We hypothesised that, additionally, both sea spray aerosols and direct emissions from manufacturing sources contributed to the contamination of the precipitation on different spatial scales. Although further research is required to determine the relative importance of different sources to the atmosphere locally and globally, this thesis has substantially advanced the state-of-the-science by i) demonstrating the significance of an air sampling artefact discussed as an uncertainty in the scientific literature over the past decade, ii) definitively ruling out volatilisation from environmental waters as a source of PFOA to air, iii) demonstrating transfer of PFAAs from seawater to air via sea spray aerosols and thus quantifying the environmental importance of this process, and iv) ultimately demonstrating that several types of sources of PFAAs impact the global atmosphere and thus PFAA contamination patterns in precipitation. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

Les composés organiques semi-volatils (COSVs) regroupent un grand nombre de composés chimiques utilisés notamment comme substances actives ou additifs dans les matériaux de construction, de décoration et dans de nombreux produits de consommation. Les COSVs sont omniprésents dans les environnements intérieurs et fréquemment détectés dans les poussières sédimentées et dans le compartiment aérien. Cette thèse a permis de documenter les concentrations de 57 composés dans 30 logements français et d'utiliser ces mesures pour tester un modèle d'équilibre visant à prédire leur répartition dans les différents compartiments de l'environnement intérieur. De ce travail, il ressort une forte ubiquité des COSVs dans les logements étudiés. Les concentrations les plus élevées ont été observées pour les phtalates et dans une moindre mesure pour le bisphénol A, les muscs synthétiques et certains pesticides et HAPs. Ces résultats confirment l'intérêt de mieux caractériser l'exposition de la population générale aux COSVs dans l'habitat français. Les travaux portant sur le modèle d'équilibre ont montré que le coefficient de partage entre l'air et l'octanol (Koa) peut être un bon prédicteur pour estimer la concentration d'un composé donné dans un ensemble de logements. Cependant, certaines limites ont été identifiées et une meilleure caractérisation des paramètres utilisés est recommandée. / Semivolatile organic compounds (SVOCs) include a large number of chemicals compounds used as active substances or additives in building materials and in many consumer products. SVOCs are ubiquitous in indoor environments and frequently detected in settled dust and indoor air. This work has investigated indoor concentrations of 57 target compounds in 30 French dwellings and measurements were used to test an equilibrium model to predict their partitioning in indoor compartments. The results showed a strong ubiquity of SVOCs in French dwellings. The highest concentrations were measured for phthalates and to a lesser extent for bisphenol A, synthetic musks, some pesticides and PAHs. These results confirm the interest to assess human exposure to SVOCs in the French dwellings. The work on the predictive model showed that octanol/air partitioning coefficient (Koa) is a good predictor to estimate SVOC concentrations in a large number of buildings. However, some limits were identified and a better estimation of the parameters used in these models is required.

Atmospheric fine particulate matter (PM2.5), which is mostly formed in the atmosphere from precursor gases, contributes to numerous environmental and health concerns. Quantifying the ambient concentrations of PM2.5 and precursor gases can be challenging. Hence, many scientific questions about the formation, chemical composition, and gas/particle partitioning of PM2.5 remain unanswered. Ambient Ion Monitor - Ion Chromatography (AIM-IC) was characterized and utilized to measure the water-soluble composition of PM2.5 (dominated by pNH4+, pSO42-, and pNO3-) and associated precursor gases (dominated by NH3(g), SO2(g), and HNO3(g)) during two field campaigns. The AIM-IC detection limits for hourly sampling were determined to be 3 - 45 ng m-3. The response time for “sticky” gases was significantly improved with a nylon denuder membrane. A novel inlet configuration for the AIM-IC, which minimizes sampling inlet losses and carryover in sample analyses, was implemented. Measurements from the BAQS-Met 2007 campaign were utilized to assess the accuracy of the AURAMS model and investigate gas/particle partitioning in SW Ontario. Due to high sulphate levels, NH3(g) was the limiting chemical factor in the formation and gas/particle partitioning of PM2.5. The errors in the predictions of relative humidity and free ammonia were responsible for the poor agreement iii between modelled and measured pNO3- values. The AIM-IC measurements from the CalNex 2010 study were compared to the CMAQ model and utilized to investigate the gas/particle partitioning in Bakersfield, CA. Very high NH3(g) concentrations were observed, and the formation and partitioning of PM2.5 was limited by HNO3(g) and H2SO4. Evidence of rapid removal of HNO3(g) by interactions with super-micron dust particles, and possibly with the alkaline surface was found. CMAQ exhibited significant biases in the predicted concentrations of pSO42-, NH3(g) and HNO3(g).

Atmospheric fine particulate matter (PM2.5), which is mostly formed in the atmosphere from precursor gases, contributes to numerous environmental and health concerns. Quantifying the ambient concentrations of PM2.5 and precursor gases can be challenging. Hence, many scientific questions about the formation, chemical composition, and gas/particle partitioning of PM2.5 remain unanswered. Ambient Ion Monitor - Ion Chromatography (AIM-IC) was characterized and utilized to measure the water-soluble composition of PM2.5 (dominated by pNH4+, pSO42-, and pNO3-) and associated precursor gases (dominated by NH3(g), SO2(g), and HNO3(g)) during two field campaigns. The AIM-IC detection limits for hourly sampling were determined to be 3 - 45 ng m-3. The response time for “sticky” gases was significantly improved with a nylon denuder membrane. A novel inlet configuration for the AIM-IC, which minimizes sampling inlet losses and carryover in sample analyses, was implemented. Measurements from the BAQS-Met 2007 campaign were utilized to assess the accuracy of the AURAMS model and investigate gas/particle partitioning in SW Ontario. Due to high sulphate levels, NH3(g) was the limiting chemical factor in the formation and gas/particle partitioning of PM2.5. The errors in the predictions of relative humidity and free ammonia were responsible for the poor agreement iii between modelled and measured pNO3- values. The AIM-IC measurements from the CalNex 2010 study were compared to the CMAQ model and utilized to investigate the gas/particle partitioning in Bakersfield, CA. Very high NH3(g) concentrations were observed, and the formation and partitioning of PM2.5 was limited by HNO3(g) and H2SO4. Evidence of rapid removal of HNO3(g) by interactions with super-micron dust particles, and possibly with the alkaline surface was found. CMAQ exhibited significant biases in the predicted concentrations of pSO42-, NH3(g) and HNO3(g).