摘要：Tropospheric mixing ratios of reactive trace gases (ozone, sulphur dioxide, nitric oxide and nitrogen dioxide) together with meteorological parameters were measured at SMEAR Estonia (Järvselja, Estonia) from August 2013 until May 2015. Seasonal monthly median mixing ratios of the trace gases were determined. Data of incoming wind directions were used to divide the site into four quadrants to compare the median mixing ratios among quadrants. We calculated 48-hour back-trajectories from January to May 2015 for days with different trace gas mixing ratios to determine the influence of pollutant transport and the impact of local processes on ambient mixing ratios. Overall, long-distance transport contributed to 15% of the total concentrations measured. The data demonstrate that distant air masses carrying higher pollutant concentrations, in particular from eastern directions, significantly contributed to local SO2 and NOx mixing ratios. Otherwise, the SMEAR Estonia station is a rural site with pollutant mixing ratios near to the measurement equipment’s detection limit.
