2013 Progress Report: Sources and Radiative Properties of Organosulfates in the AtmosphereEPA Grant Number: R835401
Title: Sources and Radiative Properties of Organosulfates in the Atmosphere
Investigators: Stone, Elizabeth A
Institution: University of Iowa
EPA Project Officer: Hunt, Sherri
Project Period: April 1, 2013 through March 31, 2016
Project Period Covered by this Report: April 1, 2013 through March 31,2014
Project Amount: $300,000
RFA: Anthropogenic Influences on Organic Aerosol Formation and Regional Climate Implications (2012) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Global Climate Change , Climate Change , Air
This project focuses on the measurement of organosulfates in the 2013 Southern Oxidant & Aerosol Study (SOAS). The aim is to identify the biogenic and anthropogenic emissions sources which lead to formation of organosulfates and how mixtures of biogenic and anthropogenic emissions lead to secondary organic aerosol formation. Laboratory studies will investigate the impacts of organosulfates on climate, including their radiative properties, light absorption, and their impact on cloud condensation nuclei.
To allow for organosulfate quantification in ambient aerosol, a novel set of biogenic organosulfate molecules is being synthesized. The target molecules include small, isoprene-derived organosulfates that have previously been identified in smog chamber and ambient aerosol studies. To date, four of eight target standards have been synthesized, purified, and characterized. These standards are among the first organosulfate standards developed, which are critical to the development of accurate measurement methods. Furthermore, these standards will allow for the characterization of the physical and climate-relevant properties of organosulfates in the atmosphere.
With the newly developed organosulfate standards, a new analytical method has been developed using ultra-performance liquid chromatography (UPLC) and tandem mass spectrometry (MS/MS) for the separation, identification, and quantification of atmospheric organosulfates. Importantly, the method is demonstrated to be linear across a range of concentrations that encompass levels observed in atmospheric aerosols, has a low limit of detection, and excellent reproducibility for most compounds. The separation method specifically targets the retention and resolution of small, highly-polar and ionic organosulfates which are not retained on conventional reversed-phase UPLC columns. Hence, this new method fills a significant gap in the current methods of organosulfate analysis. In addition, an efficient method of preparing ambient samples for UPLC-MS/MS analysis has been developed, validated, and tested on ambient samples collected in Centreville, Alabama during the Southeastern Oxidant and Aerosol Study (SOAS). The newly developed sample preparation and instrumental analysis methods will next be applied to temporally-resolved sets fine particulate matter (PM2.5) collected during the SOAS field campaign following the day/night and intensive sampling schedules.
Complementary measurements of PM2.5, including organic carbon (OC), elemental carbon (EC), and organic species have also been completed through this research project. We have analyzed 110 samples for elemental and organic carbon (EC and OC), 30 samples for water-soluble organic carbon (WSOC), and 52 samples for organic species using gas chromatography mass spectrometry (GCMS). The quantified organic compounds include 13 n-alkanes which serve as markers of vegetative detritus, 20 n-alkanoic acids some of which are emitted by food cooking and vegetation, six unsaturated fatty acids, seven dicarboxylic acids which are suggested SOA tracers, 11 SOA tracers of biogenic gases, levoglucosan and five sterols that are tracers for biomass burning. These data provide insight to the bulk composition of PM2.5, will be used in source apportionment modeling, and provide opportunities for measurement inter-comparisons with other SOAS researchers to assess sampling and measurement artifacts and the accuracy of emerging methods of aerosol analysis.
- Further development of organosulfate standards, with focus on the target compounds initially proposed and additional compounds with strong analytical signals, suggesting high atmospheric abundance.
- Chemical analysis of organosulfates in PM2.5 samples in Centreville during SOAS following the day/night and intensive periods and analysis of these data to evaluate changes in OS concentrations in response to sulfur gas emissions, aerosol acidity, and meteorological conditions (i.e. temperature, relative humidity, and sunlight).
- Receptor-based source apportionment modeling by two approaches (positive matrix factorization and chemical mass balance) to quantify anthropogenic and biogenic contributions to organic aerosol (particularly SOA).
- Preliminary characterization of the physical and climate-relevant properties of atmospheric organosulfates (i.e., light absorption and cloud condensation nucleation activity)
- Preparation and submission of manuscripts for publication.
- Measurement inter-comparison with other SOAS researchers