Comparison between summertime and wintertime Arctic Ocean primary marine aerosol properties
Primary marine aerosols (PMAs) are an important source of cloud\ncondensation nuclei, and one of the key elements of the remote marine\nradiative budget. Changes occurring in the rapidly warming Arctic, most\nimportantly the decreasing sea ice extent, will alter PMA production and\nhence the Arctic climate through a set of feedback processes. In light\nof this, laboratory experiments with Arctic Ocean water during both\nArctic winter and summer were conducted and focused on PMA emissions as\na function of season and water properties. Total particle number\nconcentrations and particle number size distributions were used to\ncharacterize the PMA population. A comprehensive data set from the\nArctic summer and winter showed a decrease in PMA concentrations for the\ncovered water temperature (T-w) range between - 1 degrees C and 15\ndegrees C. A sharp decrease in PMA emissions for a T-w increase from -1\ndegrees C to 4 degrees C was followed by a lower rate of change in PMA\nemissions for T-w up to about 6 degrees C. Near constant number\nconcentrations for water temperatures between 6 degrees C to 10 degrees\nC and higher were recorded. Even though the total particle number\nconcentration changes for overlapping T-w ranges were consistent between\nthe summer and winter measurements, the distribution of particle number\nconcentrations among the different sizes varied between the seasons.\nMedian particle number concentrations for a dry diameter (D-p) < 0.125\nmu m measured during winter conditions were similar (deviation of up to\n3 %), or lower (up to 70 %) than the ones measured during summer\nconditions (for the same water temperature range). For D-p > 0.125 mu m,\nthe particle number concentrations during winter were mostly higher than\nin summer (up to 50 %). The normalized particle number size\ndistribution as a function of water temperature was examined for both\nwinter and summer measurements. An increase in T-w from -1 degrees C to\n10 degrees C during winter measurements showed a decrease in the peak of\nrelative particle number concentration at about a D-p of 0.180 mu m,\nwhile an increase was observed for particles with D-p > 1 mu m. Summer\nmeasurements exhibited a relative shift to smaller particle sizes for an\nincrease of T-w in the range 7-11 degrees C. The differences in the\nshape of the number size distributions between winter and summer may be\ncaused by different production of organic material in water, different\nlocal processes modifying the water masses within the fjord (for example\nsea ice production in winter and increased glacial meltwater inflow\nduring summer) and different origin of the dominant sea water mass.\nFurther research is needed regarding the contribution of these factors\nto the PMA production.