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Dynamics of carbon dioxide and energy exchange over a small boreal lake were investigated.Flux measurements have been carried out by the eddy covariance technique during two open-water periods (June-October) at Lake Kuivajärvi in Finland. Sensible heat (H) flux peaked in the early morning, and upward sensible heat flux at night results in unstable stratification over the lake. Minimum H was measured in the late afternoon, often resulting in adiabatic conditions or slightly stable stratification over the lake. The latent heat flux (LE) showed a different pattern, peaking in the afternoon and having a minimum at night. High correlation (r 2 = 0.75) between H and water-air temperature difference multiplied by wind speed (U) was found, while LE strongly correlated with the water vapor pressure deficit multiplied by U (r 2 = 0.78). Monthly average values of energy balance closure ranged between 70 and 99%. The lake acted as net source of carbon dioxide, and the measured flux (F CO2 ) averaged over the two open-water periods (0.7 μmol m À2 s À1) was up to 3 times higher than those reported in other studies. Furthermore, it was found that during period of high wind speed (>3 m s À1) shear-induced water turbulence controls the water-air gas transfer efficiency. However, under calm nighttime conditions, F CO2 was poorly correlated with the difference between the water and the equilibrium CO 2 concentrations multiplied by U. Nighttime cooling of surface water enhances the gas transfer efficiency through buoyancy-driven turbulent mixing, and simple wind speed-based transfer velocity models strongly underestimate F CO2 .

Abstract. We have analyzed one year (July 2006-July 2007 of measurement data from a relatively clean background site located in dry savannah in South Africa. The annualmedian trace gas concentrations were equal to 0.7 ppb for SO 2 , 1.4 ppb for NO x , 36 ppb for O 3 and 105 ppb for CO. The corresponding PM 1 , PM 2.5 and PM 10 concentrations were 9.0, 10.5 and 18.8 µg m −3 , and the annual median total particle number concentration in the size range 10-840 nm was 2340 cm −3 . During Easterly winds, influence of industrial sources approximately 150 km away from the measurement site was clearly visible, especially in SO 2 and NO x concentrations. Of gases, NO x and CO had a clear annual, and SO 2 , NO x and O 3 clear diurnal cycle.Atmospheric new-particle formation was observed to take place in more than 90% of the analyzed days. The days with no new particle formation were cloudy or rainy days. The formation rate of 10 nm particles varied in the range of 0.1-28 cm −3 s −1 (median 1.9 cm −3 s −1 ) and nucleation mode particle growth rates were in the range 3-21 nm h −1 (median 8.5 nm h −1 ). Due to high formation and growth rates, observed new particle formation gives a significant contribute to the number of cloud condensation nuclei budget, having a potential to affect the regional climate forcing patterns.

Abstract. This study is based on 18 months (20 July 2006-5 February 2008) of continuous measurements of aerosol particle size distributions, air ion size distributions, trace gas concentrations and basic meteorology in a semi-clean savannah environment in Republic of South Africa. New particle formation and growth was observed on 69% of the days and bursts of non-growing ions/sub-10 nm particles on additional 14% of the days. This new particle formation frequency is the highest reported from boundary layer so far. Also the new particle formation and growth rates were among the highest reported in the literature for continental boundary layer locations; median 10 nm formation rate was 2.2 cm −3 s −1 and median 10-30 nm growth rate 8.9 nm h −1 . The median 2 nm ion formation rate was 0.5 cm −3 s −1 and the median ion growth rates were 6.2, 8.0 and 8.1 nm h −1 for size ranges 1.5-3 nm, 3-7 nm and 7-20 nm, respectively. The growth rates had a clear seasonal dependency with minimum during winter and maxima in spring and late summer. The relative contribution of estimated sulphuric acid to the growth rate was decreasing with increasing particle size and could explain more than 20% of the observed growth rate only for the 1.5-3 nm size range. Also the air mass history analysis indicated the highest formation and growth rates to be associated with the area of highest VOC (Volatile Organic Compounds) emissions following from biological activity rather than the highest estimated sulphuric acid concentrations. The frequency of new particle formation, however, increased nearly monotonously with the estimated sulphuric acid reaching 100% at H 2 SO 4 concentration of 6 · 10 7 cm −3 , which suggests the formation and growth to be independent of each other.