Observations on gaseous and aerosols components of the atmosphere and their relationships

Measurements of sulphur dioxide, ozone, ammonia, and soluble inorganic comp onents of the atmospheric aerosol were made at a site in central southern E ngland. Ammonia, ozone, and nitrate aerosol in winter were shown to exhibit significant diurnal variation. Ozone showed a typical diurnal variability, the magnitude of which was dependent upon wind speed. The lower night-time ozone concentrations at lower wind speeds were attributed to depletion ins ide nocturnal boundary layers by dry deposition. Ammonia, in contrast, show ed a different behaviour, whereby the diurnal cycle was more pronounced at higher wind speeds, indicating that the cycle was unlikely to be the result of dry deposition at night. Ammonia concentrations showed a temperature de pendence and the diurnal cycle of ammonia at this site appears to be the re sult of a temperature-driven emission signal. Of the total reduced nitrogen , NHx (NHx = NH3 + NH4+ aerosol), the phase was dominant and it is likely t hat more than 60% of the boundary layer NHx is in this phase. The loss term of ammonia by reaction with acid sulphate aerosol is likely to be greater than that by dry deposition on a UK scale. Nitrate aerosol showed a positiv e correlation with sodium aerosol, once the effect of mutual correlations w ith sulphate and ammonium were removed. This correlation effect, in combina tion with evidence of a marine-oriented directional dependence of nitrate a erosol, and negative non sea-salt chloride aerosol from the same 'marine' s ector, shows the potential importance of the formation of sodium nitrate ae rosol from reaction of dinitrogen pentoxide, or possibly nitric acid or nit rogen dioxide with sodium chloride aerosol. It is likely that this provides the major route of nitrate into rain, not the scavenging of nitric acid va pour. Aerosol sulphate, nitrate, and ammonium have been measured at Harwell since 1954. Sulphate aerosol increased up until 1976 and has declined subs equently. Nitrate aerosol has increased over the whole period, whereas ammo nium aerosol follows a similar pattern to that of sulphate, but with an equ ivocal direction of trend after 1976. Sulphate, nitrate and ammonium aeroso l all show a similar statistically significant seasonality. A historical in ventory of ammonia emissions shows a clear correlation with ammonium aeroso l.