Long-term trends of primary and secondary pollutant concentrations in Switzerland and their response to emission controls and economic changes

A detrending technique is developed for short-term and yearly variations in order to identify long-term trends in primary and secondary pollutants. In this approach, seasonal and weekly variations are removed by using a mean year, the residual meteorological short-term variation is removed by using a multiple linear regression model. This methodology is employed to detrend ozone (O-3), NOx, VOC and CO concentrations in Switzerland. We show that p rimary pollutants (NOx,VOC and CO) at urban and sub-urban stations show a d ownward trend over the last decade which correlates well with the reduction s in the estimated Swiss emissions. In spite of these large decreases achie ved in precursor emissions, summer peak ozone concentrations do not show an y statistically significant trend over the last decade. Application of this method to ozone concentrations measured at the Jungfraujoch (3580 m a.s.l. ) also shows no trend over the last 10 years. Detrended summer ozone correl ates well with European Union gross national product and industrial product ion growth rates. These results suggest that if substantial reductions in s ummer peak ozone in Switzerland are desired, emissions reduction strategies must be part of control program involving a much larger region. (C) 2001 E lsevier Science Ltd. All rights reserved.