Jeffrey S. Gaffney — University of Arkansas, Little Rock
Nancy A Marley — University of Arkansas, Little Rock
Gail Bridges — University of Arkansas, Little Rock
Angie Marchany-Rivera — LHS HARMON - Science Department
Mahuba Begum — University of Arkansas, Little Rock
Category
Aerosol Properties
Description
Rain impacts on AEAs and BC levels (absorption at 880 nm). Note that significant BC remains even during heavy rain events, while AEAs show loss of UV-absorbing compounds during rain events.
Atmospheric aerosols and their links to clouds are one of the main focus areas of the Department of Energy’s Atmospheric System Research, particularly as they affect regional climate. Aerosol lifetimes depend on the aerosol’s ability to uptake water and grow to sufficient size to be either removed by gravitational settling, act as cloud condensation nuclei, or be removed by precipitation scavenging. The investigation of UV-visible absorbing aerosols is underway using a seven-channel aethalometer to evaluate the change in optical absorption during precipitation events. Angstrom absorption exponents (AAEs) are determined before, during, and after rain events to examine the changes in AAEs anticipated by removal of shortwave-absorbing organic species (i.e. carboxylates) that are produced by biogenic emissions (isoprene, monoterpenes, and sesquiterpenes). Black carbon data taken at the University of Arkansas at Little Rock and other sites clearly show that a significant amount of absorbing carbon is not removed during rain events, and that the organic matter removed is likely secondary organics from biogenic sources as indicated by lower AAEs . The determinations of dissolved organic carbon (DOC) and natural radionuclides in precipitation are also used to help examine the carbonaceous aerosol removal during rain events. This work suggests that carbonaceous aerosols will have different lifetimes depending on their aqueous solubilities (non-polar or polar) and their morphologies (i.e., organic coatings on non-polar materials or polar materials or as separate organic aerosol species). The work also indicates that equilibrium may exist between semi-volatile water-soluble organics and aerosol surfaces that act to remove the oxidized organics while “black carbon” is not removed. The data are discussed in terms of the potential impacts of anthropogenic enhancement of secondary organic aerosols that are absorbing radiation and adding to atmospheric heating, and their anticipated lifetimes.
