Ion and particle number concentrations and size distributions along the Trans-Siberian railroad

Aerosol concentrations and properties in Russia are not well known. There are only few studies published on aerosols in Russia. However, these aerosols can have a major effect on global climate. We measured aerosol particle and air ion number size distributions tooether with relevant information on meteorolo ical conditions and atmospheric trace gas 9 concentrations in Russia. Our purpose was to get new insight on number concentrations of aerosol particle and air ions in different parts of Russia, and to examine which sources and sinks affected the observed concentrations. During a two-week TROICA-9 expedition between 4 and 18 October 2005, we travelled on the Trans-Siberian railroad from Moscow to Vladivostok and back, conducting measurements constantly along the route. The lowest aerosol particle number concentrations, around 500 cm(-1), were observed at remote sites and the highest concentrations of around 40 000 cm(-1) were observed near large industrial towns. The particle number concentration correlated best with nitrogen oxide and carbon monoxide concentrations. Pollutant levels were at their highest in the vicinity of towns, even though important pollution sources such as wood burning and forest fires also existed in rural areas. Concentrations of positive and negative intermediate and large ions were of the same order of magnitude as has been observed in previous studies made in boreal forests. Concentrations of intermediate ions were often low of the order of a few ions cm-', but their concentration increased during nucleation, rain and snowfall events. Concentrations of positive and negative cluster ions were sometimes very high, reaching values of about 5000 cm(-1) in case of negative ions. We also detected exceptionally high ion production rates of up to 30 s(-1) cm(-1) due to 222-radon decay. Concentrations of cluster ions correlated quite well with the ion production rate but less so with the ion sink. Two particle formation events were observed, during which the particle growth rates varied between 2.4 and 11.4 urn h(-1). Smaller particles grew slower than the bigger ones.