10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Hygroscopicity and Mixing State of Fine Aerosols in the South Eastern Mediterranean Sea and around the Arabian Peninsula during the AQABA Campaign
SPYRIDON BEZANTAKOS, Konstantinos Barmpounis, Michael Pikridas, George Biskos, The Cyprus Institute, Nicosia, Cyprus
Abstract Number: 1534 Working Group: Aerosols in Earth System
Abstract Ultrafine aerosol particles in the atmosphere affect the global climate by absorbing and scattering radiation and by acting as Cloud Condensation Nuclei (CCN). Due to the high variability of their physical and chemical properties, however, quantifying their contribution on climate is a challenging task. Particle properties may change depending on the activity of their sources and the meteorological conditions. In addition their mixing state can vary with time and location. Having information about the variation of the properties and the mixing state is therefore very important for understanding the contribution of atmospheric particles on climate.
Here we report the hygroscopicity and mixing state of fine aerosol particles (i.e., particles having dry mobility diameters from 60 to 160 nm), which were measured using a custom made hygroscopic tandem differential mobility analyzer (HTDMA) during the Air Quality and climate change in the Arabian Basin (AQABA) ship based campaign that was conducted from early July to the end of August 2017. The ship crossed the southeastern Mediterranean Sea (SEMED), the Red Sea (RS) and circulated the Arabian peninsula (AP). All these areas pose an increased climate and health related scientific interest as they are affected by multi-source, multi-regional aerosols, which interact, depending on the meteorology patterns. In addition, measurements reporting the physicochemical properties of aerosol, and more specifically its hygroscopicity, are scarce in the middle east, in contrast to the SEMED region. Except from the hygroscopic growth of the sampled aerosols, which is directly derived from the HTDMA measurements we also report their mixing state and their apparent κ-value, connected with different wind patterns, across the path of the ship. A first analysis of the results shows that the apparent hygroscopic parameter κ of the fine aerosol fraction maxed at approx. 0.4 throughout the campaign, excluding times when the measurements were affected by our ship plumes. Larger (e.g., accumulation mode) particles exhibited values close to this maximum in the proximity of the gulf of Oman, while in the majority being internally mixed, which is indicative of aged/long transported particles, containing a significant amount of sulfates or other highly hygroscopic material. In contrast, the smallest (i.e., 60 nm) aerosols exhibited lower κ values, possibly due to increased soot content, while their highest hygroscopicity was observed in the SEMED region, south of the island of Crete, due to the Etesian outflow. Highest fractions of externally mixed particles in all sampled sizes were observed in the Suez canal due to increased density of local sources (e.g., ship traffic).