Comparison between summertime and wintertime Arctic Ocean primary marine aerosol properties
Primary marine aerosols (PMA) are an important source of cloud condensation nuclei, and one of the key elements of the remote marine radiative budget. Changes occurring in the rapidly warming Arctic, most importantly the decreasing sea ice ex- 5 tent will alter PMA production and hence the Arctic climate through a set of feedback processes. In light of this, laboratory experiments with Arctic Ocean water during both Arctic winter and summer were conducted and focused on PMA emissions as a function of season and water properties. Total particle number concentrations and particle number size distributions were used to characterize the PMA population. A compre10 hensive data set from the Arctic summer and winter showed a decrease in PMA concentrations for the covered water temperature (Tw) range between −1 C and 15 C. A sharp decrease in PMA emissions for a Tw increase from −1C to 4 C was followed by a lower rate of change in PMA emissions for Tw up to about 6 C. Near constant number concentrations for water temperatures between 6 C to 10 C and higher were 15 recorded. Even though the total particle number concentrations changes for overlapping Tw ranges were consistent between the summer and winter measurements, the distribution of particle number concentrations among the different sizes varied between the seasons. Median particle number concentrations for Dp < 0.125μm measured during winter conditions were similar (deviation of up to 3 %), or lower (up to 70 %) than the 20 ones measured during summer conditions (for the same water temperature range). For Dp > 0.125μm, the particle number concentrations during winter were mostly higher than in summer (up to 50 %). The normalized particle number size distribution as a function of water temperature was examined for both winter and summer measurements. An increase in Tw from −1C to 10 C during winter measurements showed a 25 decrease in the peak of relative particle number concentration at about Dp of 0.180 μm, while an increase was observed for particles with Dp > 1μm. Summer measurements exhibited a relative shift to smaller particle sizes for an increase of Tw in the range 7– 11 C. The differences in the shape of the number size distributions between winter and 31154 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | summer may be caused by different production of organic material in water, different local processes modifying the water masses within the fjord (like sea ice production in winter and increased glacial melt water inflow during summer) and different origin of the dominant sea water mass. Further research is needed regarding the contribution 5 of these factors to the PMA production.