OBJECTIVES: This study attempted to develop a simple statistical model for assessing the contribution of aerosols transported regionally and those transported long range to the concentrations of fine particulate matter (PM) in urban air in Helsinki. METHODS: The construction and testing of the linear regression model was based on PM measurement data from two locations in the City of Helsinki (Vallila & Kallio) and on ion concentration data obtained from the three nearest monitoring stations of The Co-operative Programme for Monitoring and Evaluating of the Long-range Transmission of Air Pollutants in Europe (EMEP). The "ion sum" was calculated on the basis of the following daily measured EMEP parameters in 1998-2000: (i) sulfate (SO), (ii) the sum of nitrate (NO) and nitrogen acid (HNO), and (iii) the sum of ammonium (NH) and ammonia (NH). The ion sum was compared with sulfate as the proxy variable for long-range transmission. RESULTS: The correlation of the daily average PM concentration with the ion sum (R = 0.59-0.61) was higher than that with sulfate (R = 0.48-0.50). The regression estimates showed relatively small year-to-year variation. The contribution of long-range transportation to the measured PM concentration in urban air in Helsinki was estimated to be 64-76%. CONCLUSIONS: The results showed a strong association between the ion sum interpolated from the EMEP data and the PM concentration measured at urban sites in Helsinki. This association can be utilized in local dispersion modeling of PM concentrations in urban air.