Fog Induced Aerosol Modification Observed by AERONET, Including Occurrences During Major Air Pollution Events

Friday, 18 December 2015: 11:05
3002 (Moscone West)
Thomas F Eck1,2, Brent N Holben1, Jeffrey S. Reid3, David Matthew Giles4, Miguel Rivas5, Ramesh P Singh6, Sachchida Nand Tripathi7, Carol J Bruegge8, Zhengqiang Li9, Steven E Platnick1, Thomas Arnold1, Richard Anthony Ferrare10, Chris A Hostetler10, Sharon P Burton10, Jhoon Kim11, Young J Kim12, Alexander Sinyuk1,4, Oleg Dubovik13, Antti T Arola14, Joel Schafer1,4, Paulo Artaxo15, Alexander Smirnov1,4, Hongbin Chen16 and Philippe Goloub13, (1)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (2)Universities Space Research Association Greenbelt, Greenbelt, MD, United States, (3)Naval Research Lab Monterey, Monterey, CA, United States, (4)Science Systems and Applications, Inc., Lanham, MD, United States, (5)Universidad de Tarapaca, Arica, Chile, (6)Chapman University, School of Earth and Environmental Sciences, Orange, CA, United States, (7)Indian Institute of Technology Kanpur, Kanpur, India, (8)Jet Propulsion Laboratory, Pasadena, CA, United States, (9)Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing, China, Beijing, China, (10)NASA Langley Research Center, Hampton, VA, United States, (11)Yonsei University, Seoul, South Korea, (12)GIST Gwangju Institute of Science and Technology, Gwangju, South Korea, (13)University of Lille 1, Laboratoire d'Optique Atmosphérique, Villeneuve d'Ascq, France, (14)Finnish Meteorological Institute, Helsinki, Finland, (15)USP University of Sao Paulo, São Paulo, Brazil, (16)Institute of Atmospheric Physics, LAGEO, Beijing, China
The modification of aerosol optical properties due to interaction with fog is examined from measurements made by sun/sky radiometers at several AERONET sites. Retrieved total column volume size distributions for cases identified as aerosol modified by fog often show very a large ‘middle mode’ submicron radius (~0.4 to 0.5 microns), which is typically seen as a component of a bimodal sub-micron distribution. These middle mode sized particles are often called cloud-processed or residual aerosol. This bimodal accumulation mode distribution may be due to one mode (the larger one) from fog-processed aerosol and the other from interstitial aerosol, or possibly from two different aerosol species (differing chemical composition) with differing hygroscopic growth factors. The size of the fine mode particles from AERONET retrieved for these cases exceeds the size of sub-micron sized particles retrieved for nearly all other aerosol types, suggesting significant modification of aerosols within the fog or cloud environment. In-situ measured aerosol size distributions made during other fog events are compared to the AERONET retrievals, and show close agreement in the residual mode particle size. Almucantar retrievals are analyzed from the Kanpur site in the Indo-Gangetic Plain in India (fog in January), Beijing (fog in winter), Fresno, CA in the San Joaquin Valley (fog in winter), South Korea (Yellow Sea fog in spring), Arica on the northern coast of Chile (stratocumulus), and several other sites with aerosol observations made after fog dissipated.

Additionally, several major air pollution events are discussed where extremely high aerosol concentrations were measured at the surface and during which fog also occurred, resulting in the detection very large fine mode aerosols (residual mode) from AERONET retrievals in some of these events. Low wind speeds that occurred during these events were conducive to both pollutant accumulation and also fog formation. The presence of fog then increases the rates of gas-to particle conversion for sulfate, nitrate and organics, in addition to increasing the mass of existing particles due to fog processing and/or hygroscopic growth. All of these major air pollution events resulted in documented very large health impacts and were all covered extensively by the media in many countries.