Analytical Chemistry Seminar: Barbara Dix and Pedro Campuzano Jost
Analytical & Environmental Chemistry Division and Atmospheric Chemistry Program Seminar
Jointly sponsored by the Department of Chemistry and Biochemistry, CIRES, and the Environmental Program
Parameterization and evaluation of airborne halogen oxide measurements in the tropical transition layer and lower stratosphere
by Barbara Dix - Sr. Research Associate, Group of Prof. Rainer Volkamer, Dept. of Chemistry and Biochemistry, University of Colorado Boulder
Tropospheric halogen oxides catalytically destroy ozone, modify oxidative capacity and oxidize atmospheric mercury. Ozone is an important precursor for OH, which determines the lifetime of methane, an important greenhouse gas. About 75% of the global tropospheric ozone and methane loss occurs at tropical latitudes, where further the ozone radiative forcing is most sensitive to changes in the ozone budget. We have measured bromine and iodine monoxide (BrO and IO) by Airborne Multi-Axis Differential Optical Absorption Spectroscopy (AMAX-DOAS) over the Western, Central and Eastern tropical Pacific Ocean. AMAX-DOAS measures solar scattered light along changing lines of sight to detect trace gases at different altitudes. Light path lengths at instrument altitude can reach up to a few hundred km in thin air, which enables detection limits of about 0.3 pptv for BrO and 0.05 pptv for IO for 60s and 30s integration time respectively. The initial result of a DOAS analysis is the integrated concentration along the line of sight, i.e. a column measurement. To derive volume mixing ratios from MAX-DOAS data typically involves the time consuming process of simulating the light path contributions to each measured spectrum by radiative transfer modeling. Here we present a method to parameterize radiative transfer, which allows for a fast conversion of column measurements into volume mixing ratios along the flight track. We will compare parameterized results with vertical profiles we retrieved by inversion techniques and discuss advantages and limitations of our new method.
SOA derived from isoprene epoxydiols: Insights into formation, aging and distribution over the continental US from two NASA aircraft campaigns
by Pedro Campuzano Jost - Research Scientist, Group of Jose Jimenez, Dept. of Chemistry and Biochemistry, University of Colorado Boulder
Isoprene-derived SOA formation has been studied extensively in the laboratory, but it is still unclear to what extent isoprene contributes to the overall SOA burden over the southeastern US, an area with both strong isoprene emissions as well as large discrepancies between modeled and observed aerosol optical depth. Under low-NO conditions, the key gas-phase intermediate is isoprene epoxide (IEPOX), which can be incorporated into the aerosol phase by sulfate ester formation, direct hydrolysis, or other mechanisms. While recent results from ground studies have established the importance of this pathway in the SE US, the overall mechanism is not well constrained, and there is a lack of data to constrain regional and global models that are starting to incorporate this new SOA pathway.
AMS measurements by our group over the continental US recorded aboard the NASA DC8 during the DC3 and SEAC4RS campaigns were used to derive the first comprehensive survey of IEPOX-SOA over the continental US up to 12 km altitude. Based on this analysis, on average 38% of SOA in the SE US boundary layer during the Summer of 2013 was IEPOX-SOA, while springtime values were considerably lower. These results are placed in the context of multiple ground studies compiled by our group, which also show considerable variability in the contribution of IEPOX-SOA to total OA.