There are two distinct research foci within this thesis; the role of aerosol particle and trace gases on (i) visibility and (ii) tropospheric chemistry. This work investigates short and long term visibility, by exploring
the combined influence of atmospheric aerosol and meteorology. Observations were fitted to a newly developed light extinction model to generate predictions of historic aerosol and gas scattering and absorbing properties, explaining long term visibility trends and their dependence on meteorological conditions. This model
incorporates parameterizations of aerosol hygroscopicity, gas absorption and particle concentration, scattering,
and absorption. Historical visibility data can therefore be used to assess trends in aerosol particle properties for time periods when observational data are scarce or non-existent.
Short term visibility variations caused by particulate matter from firework and bonfire emissions is presented. It is shown that a reduction in the atmospheric visibility nationwide is -25%; which is a consequence of increased loading of atmospheric PM, and is found to be dependent upon relative humidity. Within tropospheric chemistry, HONO is an important source of OH radicals, and daytime HONO sources are poorly constrained. This work explores the abundance of HONO during a solar eclipse as a natural short-term perturbation to atmospheric photochemistry. A chemical kinetic model is employed to predict the concentrations of HONO using different source scenarios. The study provides insights into the variation of HONO with meteorology, traffic emission and other source.