AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Estimation of Organo-Sulfur in PM$_(2.5) via Isotope Dilution ICPMS and Ion Chromatography
ERIC EDGERTON, Karsten Baumann, Mike Fort, Stephanie Shaw, John Jansen, Atmospheric Research & Analysis
Abstract Number: 400 Working Group: Air Quality and Climate in the Southeast US: Insights from Recent Measurement Campaigns
Abstract Production of secondary organic aerosol (SOA) involves a host of oxidation mechanisms for biogenic and anthropogenic VOCs and SVOCs. Some of these pathways may involve acid catalysis and produce a variety of sulfur-containing organic compounds in the condensed phase, such as isoprene epoxydiol sulfates. Information on total organic sulfur concentrations in PM$_(2.5) is therefore useful for constraining SOA production mechanisms in atmospheric models and for comparison with measurements based on direct analysis of individual organo-sulfur compounds. The purpose of this presentation is to describe an analytical technique for estimating total organo-sulfur in PM$_(2.5), and to present initial results of analyses for samples collected at several sites in the southeastern U.S.
Organo-sulfur is estimated as the difference between total-S and sulfate-S in gravimetrically prepared aqueous extracts of PM$_(2.5) from Teflon filters. Sulfate-S is analyzed via traditional ion chromatography (IC). Total-S is determined by isotope dilution dynamic reaction cell ICPMS. In this technique, sample extracts are spiked with a known mass of $^(33)SO$_4, and the three major isotopes of sulfur are quantified as $^(32)S$^(16)O (48 amu), $^(33)S$^(16)O (49 amu) and $^(34)S$^(16)O (50 amu). Total-S mass in the sample is then calculated as:
where, ($^(32)S$^(16)O) and ($^(33)S$^(16)O) are the ICPMS counts at 48 amu and 49 amu; IE$_(48) and IE$_(49)are the relative ion efficiencies for 48 amu and 49 amu; and Spike$_(33) is the spike of $^(33)SO$_4 corrected for chemical and isotopic purity.
The IC and ICPMS are both calibrated with gravimetrically prepared NIST SRM 3181 (sulfate in water) and the ICPMS is further challenged with methanesulfonic acid and camphorsulfonic acid as model organo-sulfur compounds. Based on recoveries of external standards and model organo-S compounds, the extended uncertainty of total-S is 0.6%, and the extended uncertainty of the difference between total-S and sulfate-S is 0.9%.
Results from the Jefferson Street SEARCH site show mean organo-S of 42.5 +/- 15.6 ng/m$^3 and 14.8 +/- 6.7 ng/m$^3 during August 2012 and November 2012, respectively. These concentrations correspond to 6.4 +/- 3.3% and 4.9 +/- 2.1% of total-S during August and November, respectively. Day/night observations of organo-S during the SOAS campaign at Centreville, AL will also be presented and discussed.