Transport of PAN and NOy from different source regions to the Swiss high alpine site Jungfraujoch

The effect of intercontinental transport on measurements of nitrogen oxides (NOx), peroxyacetyl nitrate (PAN) and reactive nitrogen species (NOy) at the high altitude site Jungfraujoch (3580 m asl), Switzerland, was evaluated using a combination of backward trajectories and chemical filters (NOy to carbon monoxide (CO) ratio). Mixing ratios associated with air masses transported from the planetary boundary layers (PBL) of the three continental source regions Europe, North America, and Asia, and of free tropospheric origin were characterized. The analysis was applied to PAN, NOx and NOy measurements of the period 1997-1998, and to a period more than 10 years later covering several months in 2008 and 2009-2010. The results show that the mixing ratios of PAN, NOx and NOy are largest in air advected from the European PBL. In contrast to previous studies, our results indicate that the springtime maximum in PAN and NOy mixing ratios is largely attributable to air originating from the European PBL whereas air of free tropospheric origin and intercontinental transport contribute less significantly. PAN and NOy mixing ratios in air masses classified as free tropospheric are also highest in spring but substantially lower than those influenced by European PBL air. Air masses last influenced by the North American source region show considerably lower mixing ratios of nitrogen species than European air masses suggesting that a large fraction of NOy is removed during intercontinental transport probably due to washout of soluble species such as HNO3. The seasonal contributions from different source regions to PAN mixing ratios at Jungfraujoch were evaluated. The average European contribution is highest during the warm seasons with 47-57% in 1997-1998 and 61-69% in 2009-2010. The maximum contribution of North American air masses is also observed in the warm season and was about 5-7% in 1997-1998 and 6-10% in 2009-2010. Air from Asian source regions did not make a significant contribution due to the limited number of cases of direct transport from Asia, but when they occurred the air masses contained significant pollutant levels. (C) 2012 Elsevier Ltd. All rights reserved.