Two years of continuous aerosol measurements in northern Finland

[1] An investigation of aerosol chemistry was carried out at Sevettijarvi in Finnish Lapland between September 1997 and June 1999. Aerosol particles were collected on a 2-day basis using two-stage virtual impactors and were analyzed with ion chromatography for major inorganic cations and anions and for a suite of organic acids. Aerosols were also sampled in parallel on a 4-day basis for the analysis of organic carbon (OC) and black carbon (BC). The average total mass is about 3 mug m(-3) and does not significantly vary according to the season or the type of air mass. The major chemical components are sulfate, sea salts, and organic carbon, which account together for more than 80% of the total aerosol mass. BC, ammonium, nitrate, methanesulfonic acid, and the estimated crustal fraction each accounts for a few percent at most in any situation. Non-sea-salt (nss) sulfate concentrations are maximum during late winter and spring, related to the Arctic haze, associated with increased concentrations in BC, ammonium, and nss K+. The organic fraction is at its lowest in winter, as are the concentrations of most organic acids. OC and short-chain organic acid concentrations increase during springtime, which may be due to enhanced photochemistry at polar sunrise. The chemical profile is rather different during summer, with a strong decrease of the anthropogenic fraction and a larger occurrence of episodic marine events. However, the main characteristic is the very large increase in OC concentrations, which is the main component of the aerosol at that time and may be linked with local and regional enhanced biogenic activity. The aerosol at Sevettijarvi presents some specificity compared with other Arctic sites, with a much smaller impact of Arctic haze and marine events in winter and a much larger impact of biogenic sources in summer. The low contribution of the crustal fraction indicates low occurrences of transport of desert dust from Eurasia. The time series of concentrations indicate a large variability in the chemical profiles on short timescales, linked with changes in the origin of the air masses. It shows that even purely marine aerosol still comprises about 10% of nss sulfate associated with BC and OC. The profile in the continental case is largely dominated by nss sulfate, with strong increases in the ammonium and BC fractions.