The aim of this research is to understand how mid-latitude weather systems ventilate pollutants out of the boundary layer. Specifically, which regions of the boundary layer beneath mid-latitude weather systems can exchange air with the troposphere which physical processes act to transport pollutants, and what controls the amount of ventilation. These questions are investigated by simulating dry baroclinic life cycles in the presence of a boundary-layer parameterisation scheme with a passive tracer included to represent pollutants.

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No description available.

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No description available.

Methane (CH4) is a potent greenhouse gas with a radiative forcing efficiency 21 times greater than that of carbon dioxide (CO2) and an atmospheric lifetime of approximately 12 years. Although the annual global source strength of CH4 is fairly well constrained, the temporal and spatial variability of individual sources and sinks is currently less well quantified. In order to constrain CH4 emission estimates, inversion models require satellite retrievals of XCH4 with an accuracy of < 1-2%. However, satellite retrievals of XCH4 in the shortwave infrared (SWIR) are often hindered by the presence of atmospheric aerosols and/or thin ice (cirrus) clouds which can lead to biases in the resulting trace gas total column of comparable magnitude. This thesis aims to quantify the magnitude of retrieval errors caused by aerosol and cirrus cloud induced scattering for the Full Spectral Initiation Weighting Function Modified Differential Optical Absorption Spectroscopy (FSI WFM-DOAS) retrieval algorithm. A series of sensitivity tests have been performed which reveal that a) for scenes of high optical depth, accurate aerosol a priori data is required to reduce retrieval errors, b) retrieval errors due to aerosol and ice cloud scattering are highly dependent on surface albedo, SZA and the altitude at which scattering occurs and c) errors induced in global retrievals by the presence of ice clouds (up to ~ 35%) are significantly greater than those owing to aerosols (~ 1-2%). Cloud filtering is therefore important even when employing proxy methods. Furthermore, the original FSI WFM-DOAS V2 algorithm (OFSI) has been successfully modified with improved a priori albedo and aerosol, resulting in two new versions of the retrieval: MFSI and GFSI. Initial comparison of OFSI, MFSI and GFSI retrievals of XCH4 over North America show minor improvements in retrieval error, however further comparison over regions of high optical depth are required.

Characterisation of the mechanisms and consequences of global warming is one of the most important topics in modem science. It requires a detailed investigation of the infrared properties of the constituents of the terrestrial atmosphere: gaseous, particulate and liquid. In this 'thesis Fourier-Transform Infra-Red (FTIR) Spectroscopy is Used to pro vi-de data on the absorption and scattering cross sections needed to evaluate the radiative forcing of several substances present in the terrestrial atmosphere. CF 31 is being considered as replacements for some of the highly global warming and ozone depleting gases currently used in industry. High-Resolution FTIR spectra has been recorded for CF 31 over a range of temperatures and pressures and used to calculate approximate values of its global warming potential. Aerosols may affect the terrestrial radiation budget in two ways: i) they may induce global cooling due to scattering and reflection of incident solar radiation and ii) global warming due to absorption of terrestrial infrared radiation. To asses the net contribution of these aerosols one must know the concentration and location of any aerosol and also absorption and scattering coefficients. One method of monitoring the amount of aerosol in the atmosphere is to use satellites such as - the Michelson Interferometer for Passive Atmospheric Sounding (MIP AS) or Meteostat second generation (MSG). Both the satellite retrieval of aerosol concentrations and the calculation of their scattering and absorption coefficients require knowledge of the optical properties of these aerosols. Studying the spectroscopy of aerosols has proven to be a difficult problem since aerosols settle out quickly under the influence of gravity and so have short residence times ID aerosol chambers thus, radiative properties of aerosols provide one of the largest uncertainties in atmospheric modelling. In this thesis an 'acoustic trap' has been developed to counteract gravity allowing us to record spectra of some common atmospheric aerosols: volcanic ash, coal soot and sand. Descriptions of the design of this novel trap and methods for its effective use are presented along with suggestions for further improvements.

Nitrogen Dioxide (N02) is detrimental to human health. It is difficult to map accurately, as concentrations can vary greatly over small distances. Current mapping methods do not fully utilise monitored data, and as such the objective of this project was to apply new techniques based on both modelled and measured data. This was achieved through geostatistical estimation and simulation techniques. Measured N02 from automatic and diffusion tube monitoring was the primary dataset. The secondary dataset consisted of dispersion modelled NOx data at a lkm2 scale for the UK. NOx is useful for informing N02 prediction, given that N02 is a constituent pollutant of NOx• The key geostatistical estimation techniques investigated were simple kriging (SKL ordinary kriging (OK) and simple kriging with a locally varying mean (SKim). The geostatistical simulation analysis applied Sequential Gaussian Simulation (SGSIM). SK and OK can only utilise a single dataset. SKim differs from in that additional data can be inputted to inform prediction, and hence potentially reduce uncertainty. Supplementary secondary data can be highly beneficial, particularly when the primary dataset is not evenly spatially distributed. The secondary data (NOx dispersion modelled data) were used to define the locally varying mean in SKim, for both the geostatistical and simulation analyses, using two regression approaches: (i) global regression (GR) and (ii) geographically weighted regression (GWR). SKim with GWR defined locally varying means was further investigated through examination of various parameters. Throughout, the effects of other variables that may affect prediction were also discussed. The integration of the local model into the geostatistical algorithm produced an increase in estimation accuracy (measured through a reduction in uncertainty), in comparison to other techniques. SKim with GWR defined locally varying means, produced the most accurate predicted and simulated outputs of all approaches tested in this research.

The results from the laboratory experiments of iodine oxide particle (lOP) formation processes and properties are presented. The formation and growth of lOPs, originating from molecular iodine precursor, have been studied at 293 K as a function of water vapour and sulphuric and oxalic acids vapour. Under dry conditions, a linear variation in total lOP mass in particles was observed for a range of iodine concentrations. The observed hygroscopic growth factors of <1 at RH 10 - 90% on addition of H20 vapour to the particles formed under dry conditions are consistent with the particles having a fractal-like, aggregated structure. The uptake of sulphuric acid vapour onto humidified particles lead to condensational growth, with an accommodation coefficient (α) of 0.75 ± 0.05 at RH = 90% and a predicted growth rate of ~ 0.03 - 0.3 nm per hour with respect to marine boundary layer (MBl) conditions. In contrast, growth of particles exposed to oxalic acid vapour was not observed on the experimental timescales employed, indicating an upper limit for ex of 10-3• The deliquescence behaviour of crystalline HI03 and 1205 at 273 - 303 K, and the properties (e.g. water activity, density, viscosity, and efflorescence) of subsaturated and saturated iodate solutions were investigated. The deliquescence of 1205 and HI03 crystals at 293 K occurred at a relative humidity of 80.8 ± 1.0% and 85.0 ± 1.0% respectively. These values are consistent with measured water activity values for saturated 1205 and HI03 solutions at 293 K of 0.80 ± 0.01 and 0.84 ± 0.01 respectively. Optical and Raman microscope studies at low relative humidity indicate that 103- solution droplets do not exhibit efflorescence and may become ultra-viscous or glassy under atmospherically relevant conditions. In the presence of humic acid, 103- photo-chemically transforms to aqueous rand soluble iodinated humic acid and the fixing of iodine within humic structures is likely to occur at aromatic 1,2 diol groups. Transfer of 12 to the gas phase from the reduction of 103- to r, shows the oscillatory behaviour of the 'Bray-Liebhafsky' reaction and is enhanced in the presence of H202 and salinity (CI). The reduction of 103- to r shows first - order loss rate of (1.1 ± 0.1) x 10-5 s-1 which corresponds to a lifetime ~ 2 days for 103- in marine aerosol. This lifetime is consistent with the THAMOD model predictions. The predicted uptake coefficient of 03 (35 ppbv i.e. an atmospherically relevant concentration) on 100 nM I solution at 293 K was determined as (7.0 ± 0.2) x 10-7 with a resulting I2 flux of (2.9 ± 0.1) x 109 cm-2 s-1 which is ~ 5 times larger than the modelled flux at Sao Vicente (Cape Verde Island) in the tropical Atlantic Ocean. v

Current concern over climate change requires that carbon (C) sources and sinks within managed landscapes are quantified so that they can be actively managed to help reduce net greenhouse gas (GHG) emissions. While some data exist for C storage in grassland and forests, potential for C sequestration in orchards is largely unknown. Initial C inventory studies in apple (Malus) orchards determined that C sequestration in soil and trees increased with stand age. This result conflicts with current commercial management which requires trees to be replaced every 30 years to reduce disease risk. The grubbingout process, where complete orchard trees are removed, liberated approximately 0.01 t C ha-I from the soil, which is very small in comparison to the C loss from removal of biomass (up to 25 t C ha-I above-ground, ca. 5 t C ha-I below-ground) and that held in the soil (ca. 80 t C ha-I). The incorporation of biochar produced from the grubbed-up apple trees offers orchards the opportunity to enhance C storage. However long-term impacts of biochar amendments on the environment remain unknown. An experiment was established to monitor Bramley apple trees in varying levels of biochar amendment (0, 5, 25 and 50 t ha-I). The results suggested that biochar had no negative effects on tree productivity and soil quality. Investigations into density, surface area, pore size distribution and water sorption were carried out to characterise the Malus-derived char. Orchard carbon footprints have been carried out to determine orchard GHG emissions and identify potential areas of C savings. Findings suggest that footprints of UK apple production are comparatively low, ranging from 0.037 to 0.182 kg C02e per kg produce. In conclusion, there is potential within UK orchards to sequester C; full C budgets need to be carried out to determine annual C sequestration.