Estimation of the long-range transport contribution from secondary inorganic components to urban background PM10 concentrations in south-western Sweden during 1986-2010

The contribution of long-range transported (LRT) to urban background PM10 concentrations was investigated from a long-term view from 1986 to 2010. Regional air concentrations of sulphate (SO42−), nitrate (NO3−), and ammonium (NH4+) were used as a sum (Cion) to investigate the contribution from these ions to the LRT PM10 concentrations at an urban background site in Gothenburg, Sweden. Utilizing backwards trajectory analysis, the LRT contribution from Cion to the urban background PM10 concentrations (LRTCion) was estimated for six unique transport pathways and related source areas. Air masses transported over eastern Europe, UK/North Sea/Denmark and the vicinity of Scandinavia were associated with high Cion concentrations observed in Gothenburg. For each pathway, multiple linear models based on the Cion concentrations were used to estimate LRTCion and PM10 at the urban background site. The performances of the multiple linear models were satisfying with R2 between estimated and observed annual mean PM10 concentrations of 0.81 during the monitoring years 1990-2010. The models were able to describe the main features of the day-to-day average PM10 concentrations, but underestimated high level values. The annual estimated LRTCion contribution decreased from 7 ± 2 μg/m3 for 1986-2000 to 5 ± 1 μg/m3 for 2001-2010. The higher LRTCion contribution was related to the transport cluster from eastern Europe, UK/North Sea/Denmark and the vicinity of South Scandinavia.