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Research Projects: Current laboratory studies

Aging of atmospheric organic species

We use our fixed-temperature, fixed-volume 7.5 m3 Teflon chamber to probe how oxidative "aging" affects the amounts and chemical composition of atmospheric organic aerosol. A particular focus of our work is the isolation of a single phase in which multigenerational aging occurs (in the gas phase, in aqueous aerosol, etc.), requiring the development of novel approaches for generating high level of oxidants within a given phase. Funding: NSF

Heterogeneous oxidation of organic aerosol

In collaboration with Kevin Wilson (Lawrence Berkeley National Laboratory) and Doug Worsnop (Aerodyne Research) we carry out flow-tube studies aimed at understanding the oxidation of particle-phase organic compounds by gas-phase OH radicals. A major focus is how chemical structure and degree of oxidation influences whether an organic molecule will undergo functionalization (which generally lowers its vapor pressure) or fragmentation (which generally increases it). Chemistry is primarily monitored with aerosol mass spectrometry, using a range of novel vaporization and ionization approaches. Funding: DOE, NSF

Atmospheric black carbon: Chemistry and optical properties

The direct climate impacts - the absorption and scattering of light - of black carbon (soot) particles are thought to be impacted by atmospheric processing, though this is highly uncertain at present. Using flow-tube and chamber techniques to age black carbon (via heterogeneous oxidation and/or the addition of secondary aerosol coatings), combined with state-of-the-art measurements of the chemical and optical properties of the particles, we hope to better understand how the climate-relevant properties of these particles evolve during their atmospheric lifetimes. This work is done in collaboration with Colette Heald (MIT) and Paul Davidovits (Boston College). Funding: EPA

Photolytic generation of secondary organic aerosol

In this project we study the formation of secondary organic aerosol (SOA) via the direct generation of key radical intermediate species. Alkoxy radicals and alkylperoxy radicals are generated from the photolysis of precursors (alkyl nitrites and alkyl iodides, respectively), and particle-phase products of their reactions are examined using aerosol mass spectrometry. The advantage of this approach is that individual reaction pathways and oxidation generations can be probed, which is not possible in standard hydrocarbon + oxidant studies. Funding: NSF, ACS-PRF

Emissions of low-volatility gas-phase organic species

While organic compounds with high vapor pressures (VOCs) and those with low vapor pressures (organic aerosol) are now routinely measured in lab and field studies, gas-phase organic compounds with vapor pressures between the two extremes (semivolatile organic compunds and intermediate-volatility organic compounds) generally are not. Thus we have developed a new mass spectrometric instrument for quantifying and chemically characterizing such species as an ensemble. This has been deployed to the field (BEACHON and SOAS), and has also been used to characterize emissions from mobile sources (aircraft and diesel engines). Funding: NOAA, EPA

Research Projects: Recent field studies

SOAS 2013
Southeastern Oxidant and Aerosol Study, Centreville, AL, June-July 2013

TCAP 2013
Two-Column Aerosol Project, Cape Cod, MA, Feb 2013 (collaboration with Dan Czizco)

BEACHON-RoMBAS 2011
Manitou Forest, CO, July-August 2011

TREX XI and XII
Traveling Research Environmental eXperience, Hawaii, January 2012, 2013

AAFEX II
Alternative Aircraft Fuel Expt
Palmdale, CA, Mar-Apr 2011

CalNex
California Nexus 2010
Pasadena, CA, summer 2010

Contact: Prof. Jesse Kroll, MIT Departments of Civil and Environmental Engineering and Chemical Engineering, jhkroll @ mit.edu