Aerosol Optical Properties and Biogenic SOA: Effect on Hygroscopic Properties and Light AbsorptionEPA Grant Number: R835411
Title: Aerosol Optical Properties and Biogenic SOA: Effect on Hygroscopic Properties and Light Absorption
Investigators: Khlystov, Andrey , Ramachandran, Subramanian
Institution: Dessert Research Institute , North Carolina State University
Current Institution: Dessert Research Institute , Carnegie Mellon University
EPA Project Officer: Hunt, Sherri
Project Period: April 1, 2013 through March 31, 2016 (Extended to March 31, 2018)
Project Amount: $398,318
RFA: Anthropogenic Influences on Organic Aerosol Formation and Regional Climate Implications (2012) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Climate Change , Air
Secondary organic aerosol (SOA) from biogenic sources is a major contributor to the global aerosol burden. It is estimated to have a profound effect on regional and global climate. There is strong evidence that biogenic SOA can influence optical properties of ambient aerosol by altering its hygroscopicity and contributing to light absorption directly via formation of brown carbon and indirectly by enhancing light absorption by black carbon (“lensing effect”). The magnitude of these effects remains highly uncertain. It was suggested that organo-nitrogen (ON) compounds are the substances responsible for formation of brown carbon in biogenic SOA. No evidence exists yet for such a link in ambient aerosol. The goal of this project is to provide comprehensive characterization of optical properties of anthropogenically-influenced biogenic SOA, its contribution to aerosol hygroscopicity and light absorption via formation of brown carbon and “lensing” effect, and investigate the link between ON and brown carbon.
A set of state-of-the-art instruments will be deployed during two field campaigns, one at the SEARCH site near Centerville, AL during the SOAS campaign in summer 2013, the other at Duke Forest site near Chapel Hill, NC in summer 2014. The two sites are strongly influenced by biogenic sources, but are different in their proximity to anthropogenic sources. Measurements will include aerosol light absorption and scattering at two wavelengths (405 nm and 532 nm); black carbon mass and its mixing state; light absorption spectra by water-soluble aerosol; ON, water soluble organic carbon and the main ionic species in the aerosol. Light absorption and scattering will be measured for both temperature- and humidity-conditioned aerosols, which will help determine absorption enhancement due to the “lensing” effect and the humidity dependence of aerosol light scattering as a function of biogenic SOA, respectively. Measurement of the Ǻngstrom Absorption Exponent over the two wavelengths, evaluation of the relative lensing effect at these two wavelengths, and light absorption properties of water-soluble aerosol will help reduce uncertainty in determining brown carbon. The amount of brown carbon will then be compared to the amount of ON to test the proposed link between the two.
This study will provide a comprehensive characterization of optical properties of biogenic SOA and their sensitivity to anthropogenic influence. Several parameters critical for climate modeling, such as absorption cross-section, single scattering albedo and sensitivity to RH, will be measured. The measurements will also provide an indirect test of brown carbon formation mechanisms proposed in smog chamber studies. One graduate student will be trained during the project. The results of the study will be widely disseminated via publications in peer-reviewed publications and presentations at professional conferences. The results of this project will help improve carbonaceous aerosol representation in air quality models, which in turn will help formulating effective strategies to combat air pollution and global climate change.