10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
The Impact of Wet Deposition on Long-Range Aerosol Transport Arriving at the Maldives
JUTTA KESTI, John Backman, Eija Asmi, Ewan O'Connor, Orjan Gustafsson, Krishnakant Budhavant, Finnish Meteorological Institute
Abstract Number: 118 Working Group: Aerosol Transport and Transformation
Abstract Wet deposition is a process where raindrops remove aerosol particles from the atmosphere. Precipitation intensity, aerosol particle size and other microphysical properties are all factors that affect the efficiency of wet deposition. This process is important but still poorly described in atmospheric models (Liu et al. 2012).
Precipitation is an important climate variable in the Maldives. During summer, the Maldives is under the influence of the Indian monsoon, which brings warm and moist marine air consisting mostly of natural aerosols from the Indian Ocean. During winter, which is the dry season, the air masses at the Maldives mainly travel from the Indian subcontinent and thus bring polluted air.
To study the effect of precipitation on long-range transported aerosol particles in the Maldives, we used two different data sets measured at the Maldives Climate Observatory of Hanimaadhoo (MCOH), one of the Atmospheric Brown Cloud (ABC) observatories (Ramana and Ramanathan, 2006). The first measurements were conducted during 2004–2008 using a Scanning Mobility Particle Sizer (SMPS.) The second measurement period was during 2014–2017, using a Differential Mobility Particle Sizer (DMPS). In addition, we collected the meteorological observation data measured at MCOH for these periods and calculated hourly back trajectories and cumulative rainfall along the trajectory for the measurement periods using HYSPLIT 4.9 model (Draxler and Hess, 1998). The meteorological data providing wind fields and precipitation for the back-trajectory model was the GDAS 1o dataset from National Center for Atmospheric Research.
The results reveal different particle size distribution shapes depending on the source region of aerosol particles; the highest concentrations were observed in outflow from India and the Indo-Gangetic plain. The particle size distributions were also affected by the precipitation intensity en route to the measurement site. The median particle number concentration during the dry season in the first measurement period 2004–2008 was 624 1/cm3 and during monsoon season 178 1/cm3. For the second measurement period, during 2014–2017, the numbers were 1647 1/cm3 for dry season and 408 1/cm3 for monsoon season.
We also studied the change in the aerosol particle size distribution shape compared to different amounts of rainfall by using the cumulative rainfall from the model and in-situ measurements with the SMPS and DMPS. The analysis was divided to cover different source regions and seasons. Impact of precipitation on size distribution shape in the tropics for different aerosol types was then elucidated and compared with previous studies made in other locations (eg. Tunved et al., 2013).
We gratefully acknowledge the staff working at the Climate Observatory of Hanimaadhoo for maintenance of the measurements.
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