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.

Syftet med examensarbetet har varit att studera kol i mindre vattendrag med hjälp av jämviktsmodellering i PHREEQC. Fokus har varit dynamik av löst icke organiskt kol (DIC) samt att förstå hur mycket koldioxid (CO2) som avges från mindre vattendrag och om den mängden har signifikant inverkan på den globala kolbalansen. Med hjälp av provtagen data från Krycklans avrinningsområde år 2003-2007 och 2009 har modellering av DIC och pCO2 utförts med målet att se förändring både över säsong och nedströms i ytvattensystemet. För att utvärdera modellen har tillhandahållen data över uppmätt pCO2 använts. Målet var att jämföra modellerade och tillhandahållna pCO2-värden för att se hur väl modellen kunde beskriva verkligheten och om den fungerade bättre för någon plats eller under vissa delar av året. Analysen visade att pCO2-värden för modellen följer uppmätta pCO2-värden förhållandevis bra. Avvikelserna var störst för en av provpunkterna (provpunkt 6). Modellerade pCO2-värden följde de uppmätta pCO2-värden bäst under vårfloden. Modellen och analys av data visade tydliga indikationer på en avgång av CO2 från vattendraget. / The purpose of this Master thesis has been to study carbon flux in creeks. Chemical equilibrium models were produced to this end using PHREEQC. Specifically, dissolved inorganic carbon (DIC) quantities have been studied in order to understand the discharge of carbon dioxide (CO2) from the creek headwaters and how that affects the global carbon balance. Modeling of DIC and pCO2 was conducted using data from 2003-2007 and 2009 sampled at two points in the Krycklan research catchment located in northern Sweden. Seasonal variation of DIC and pCO2 in the two sample points was studied as well as the difference of these quantities between the two points. Evaluation of the model was done in part by comparing predicted pCO2 values with actual values stemming from a previous study leading to an assessment of the validity of the model. One of the sample points showed larger discrepancies between predictedand actual values than the other. Studying the seasonal variation of discrepancies, they were at the minimum during the spring flood. Finally, the analysis showed clear indications of a net CO2 discharge from the creekstretch between the two sample points.

The seasonal pattern of the carbon isotope content (delta C-13) of atmospheric CO2 depends on local and nonlocal land-atmosphere exchange and atmospheric transport. Previous studies suggested that the delta C-13 of the net land-atmosphere CO2 flux (delta(source)) varies seasonally as stomatal conductance of plants responds to vapor pressure deficit of air (VPD). We studied the variation of (source) at seven sites across the United States representing forests, grasslands, and an urban center. Using a two-part mixing model, we calculated the seasonal delta(source) for each site after removing background influence and, when possible, removing delta C-13 variation of nonlocal sources. Compared to previous analyses, we found a reduced seasonal (March-September) variation in delta(source) at the forest sites (0.5 parts per thousand variation). We did not find a consistent seasonal relationship between VPD and delta(source) across forest (or other) sites, providing evidence that stomatal response to VPD was not the cause of the global, coherent seasonal pattern in (source). In contrast to the forest sites, grassland and urban sites had a larger seasonal variation in (source) (5) dominated by seasonal transitions in C-3/C-4 grass productivity and in fossil fuel emissions, respectively. Our findings were sensitive to the location used to account for atmospheric background variation within the mixing model method that determined (source). Special consideration should be given to background location depending on whether the intent is to understand site level dynamics or regional scale impacts of land-atmosphere exchange. The seasonal amplitude in delta C-13 of land-atmosphere CO2 exchange (delta(source)) varied across land cover types and was not driven by seasonal changes in vapor pressure deficit. The largest seasonal amplitudes of delta(source) were at grassland and urban sites, driven by changes in C-3/C-4 grass productivity and fossil fuel emissions, respectively. Mixing model approaches may incorrectly calculate delta(source) when background atmospheric observations are remote and/or prone to anthropogenic influence.

<p><h1>This study discusses energy and water balance in an 80-year-old deciduous Carolinian forest in the Great Lakes region in southern Ontario, Canada. The eddy covariance technique and associated meteorological and soil variables were used to make a year-round measurements of energy and water vapour fluxes from January-December,2012. This site is part of the Turkey Point Flux Station and global Fluxnet. The linear relationship between daily turbulent (sensible heat (H), latent heat (LE)) and radiative fluxes (net radiation (Rn),soil heat (G) and canopy heat storage ( S)) has a the slope of 0.75 (intercept of -15.8 Wm^-2, and a correlation coefficient, r² of 0.93) indicating a 25% deficiency in energy balance closure. The mean value of canopy albedo was 0.16 during the growing season. Maximum daily evapotranspiration (E) rate was 3.8 mm day^-1 in June, when growing is at its peak in the region. Total annual E was 400 mm, which accounted for 42% of the total annual precipitation of 950 mm. The water storage in upper soil column (1.0 m depth) was approximately 100 mm, indicating that about 450 mm of water was lost from the forest as runoff. Apart from radiation, vapour pressure deficit (D) was the dominant control on E. Maximum value of bulk surface conductance (Gs) was about 18.5 mm s^-1. Gs linearly decreased in response to increase in D. The minimum Gs values were recorded when D was maximum, i.e. 3 to 3.5 kPa. Gs also showed high sensitivity to the volumetric soil water content (ϴ), during dry periods, for example the drought event in 2012. In the growing season, the typical value of Priestley-Taylor α ranged between 0.8 to 1.2 with a maximum of 1.8, indicating a wet deciduous forest. However, the LE/Rn relationship showed a linear increase with increasing D with a low (0.26) slope, indicating a conservative response of forest E to atmospheric demand. This study provides insight into energy partitioning, the water balance and their controls in this Carolinian deciduous forest. A better understanding of evapotranspiration processes and their controls in these forests would help to better quantify water availability at local and regional scales and to evaluate the impacts of future climate change on water resources in the region.</h1></p> / Master of Science (MSc)