Safe air below EU air quality limit ? Studies of respiratory disease using primary health care data , with Case - Crossover study design

Ambient air pollution has been linked with a number of adverse respiratory health outcomes. Earlier studies have shown that population exposure to ambient air pollution increases visits to emergency rooms and hospital admissions due to respiratory complaints. Exposure in vulnerable populations has also been shown to increase mortality risks. However, there is a need to better evaluate exposure-response to more mild and moderate respiratory diseases. The aim of this thesis was to explore the acute and long-term effects of air pollution on mild, moderate and severe respiratory diseases in an area where criteria pollutant levels are generally well below or close to current air quality limits. Air pollution levels throughout the study period from 2005 till 2010 remained well within WHO and EU guidelines All four studies are of case-crossover design. Papers I, II and IV have the total number of primary health care (PHC) visits due to asthma whereas in Paper III all visits regarding respiratory ailments to PHCs, inpatient admissions, and emergency visits were analysed. In Paper II, first visit due to asthma during the study period were analysed. In all four papers, urban background air pollution monitor data was used from the year 2005 till 2010. In Paper II, a geographic information system (GIS) based dispersion model together with an emission database was used to model long-term concentrations of NO2 at the PHC clinic. Air pollution levels throughout the study period from 2005 till 2010 remained well within WHO and EU guidelines. Correlation between different air pollution monitoring stations within the same municipality was moderate to strong. In all our studies, we found an increase in the risk of PHC asthma visits with an increase in NO2 levels. We did not found any statistically significant increases for inpatient admissions or emergency room visits due to respiratory illnesses. There was weak evidence for short-term associations between air pollution and asthma may to depend on background air pollution levels. In conclusion, the air does not seem to be entirely safe below the EU air quality limit