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Project title

Evaluation of background concentrations of air pollutants in Ireland, their health significance, and development of guidelines for local assessment

Primary Funding Agency

Environmental Protection Agency

Co-Funding Organisation(s)

n/a

Lead Organisation

University of Dublin, Trinity College (TCD)

Lead Applicant

Bruce Misstear

Project Abstract

The major aim of this research was to produce a set of guidelines for the determination of background concentration and inclusion in local air quality dispersion modelling studies. In order to achieve this objective an in-depth review of background air quality in Ireland was completed focusing on NO2 and PM10. Current methods for the prediction of background concentration in Ireland and worldwide were reviewed and commonly applied methods were compared to a baseline method in terms of accuracy. All were found to produce widely varying and inaccurate results even assuming an accurate mathematical model. This research has shown that there is a significant degree of spatial and temporal variation in background NO2 and PM10 concentrations and significant diurnal and seasonal variations in NO2 and PM10 concentrations were observed at all sites. Rural background sites tend to show a delayed evening peak in NO2 and PM10 concentrations indicative of regional transport of emissions while urban and near city background sites show bi-modal variations. Much of the diurnal and long term variation in NO2 concentrations (at urban and rural sites) could be explained by traffic emissions and a regression model was developed to explain spatial variation in long term annual mean NO2 concentrations in terms traffic flow parameters. While PM10 concentrations did not display the same strength of relationship long term concentrations of both species could be related to emissions data from the region reported to the European Body of the Co-Operative Programme for Monitoring and Evaluation of the long-range Transmissions of Air Pollutants in Europe (EMEP). Detailed analysis of the relationships between various meteorological factors highlighted wind speed and wind direction as controlling factors for background NO2 and PM10 concentrations. To quantify the variation with wind speed and direction a multiple non-parametric circular kernel regression method was applied to the data. The method was found to present significant improvements over commonly applied data binning and is particularly useful for describing the variation in background concentration levels with wind speed and direction in cases where monitoring data are limited being capable of separating true and spurious peaks and estimating values for missing data points. Furthermore a default set of normalised wind speed/direction NO2 and PM10 background concentration variations representative of regional variations was developed. Analysis of air mass history using back trajectory modelling showed that while background concentrations are subject to local emissions such as road sources they are also influenced by transboundary effects. European air masses have a tendency to create higher background levels of NO2 and PM10 than Atlantic air masses and while this is not solely due to emissions (air masses from Europe are often slow moving and stagnated) effects were strong across all background sites. The frequency with which Ireland is affected by such air masses also contributed to the seasonal variation observed in background concentration levels. Thus meteorological conditions must be considered for the full duration of any background monitoring programme. Although regional air quality models predict the regional transport of emissions and are often used to provide air pollution forecasts or for the prediction of plume dispersion in emergency response they were found to be of insufficient precision and resolution to be useful for local dispersion modelling studies due to the large fluctuations in background levels of NO2 and PM10 over relatively small scales.

Grant Approved

�72,650.00

Research Hub

Healthy Environment

Research Theme

Environment and Human Health

Start Date

01/10/2007

Initial Projected Completion Date

14/09/2011