Evaluation of background concentrations of air pollutants in Ireland and the development of guidelines for local assessment

Abstract

The values adopted for the background air pollutant concentrations in local air quality dispersion modelling studies have a significant effect on the accuracy of the overall result. Current practice regarding the data sources and assumptions on background concentrations, and subsequent addition to modelled concentrations, varies widely amongst modellers within Ireland and worldwide. A review of Environmental impact assessments (EIA) showed that in many instances the background concentration is neglected entirely, or an estimate of the annual mean is made based on representative data or short term monitoring. However, the use of a constant value is rarely appropriate since background concentrations vary widely, temporally and spatially, while also displaying a large influence from meteorological factors. Generally, the aim of a modelling study is to produce total concentration values, often for EIA, and comparison to EL) limit values. Currently in Ireland nitrogen dioxide (NO2) and particulate matter of less than 10 micro grams diameter (PM10) are the two pollutants at most risk of exceeding these values and they are thus the focus of this thesis. Previous research has focused on the validation of air quality models to Irish conditions or on the study of air quality in heavily polluted areas such as kerbside or urban centre locations. However, these studies generally neglect the background concentration or conclude that it is indeed an important area and so attribute much of the observed error to this source. No detailed study specific to background concentrations in Ireland has been carried out previously. This research is based on pre-existing data and the collection of additional hourly NO2 and PM10 concentration data at a unique background site.