faculty

Professor. Atmospheric, Oceanic and Space Sciences and Chemistry
Sc.D., Massachusetts Institute of Technology

Atmospheric Chemistry: Instrument Development and Application to Field Measurements of Ozone and Reactive Nitrogen Species

Phone: (734) 763-4066
E-mail: mcarroll@umich.edu  
Fax: 734-764-5137

Nitric oxide (NO) emitted into the atmosphere is rapidly oxidized to nitrogen dioxiede (NO₂). To the extent that the oxidation of NO to NO₂ occurs through reaction with species other than ozone (e.g. peroxy radicals), the NO-NO₂ cycle results in the catalytic production of ozone (O₃). Surface level ozone appears to have increased by ~25 ppbv (or a factor of 5) in the Northern Hemisphere since the 1900s, and increased levels of ozone near the surface are believed to be closely tied to increases in, and the distribution of, anthropogenic NO_x emissions. Furthermore, it is understood that photochemical ozone production and radical chemistry are strongly dependent on NO_x levels in rural and remote environments. Quantification of the physical and chemical processes that affect the availability of NO_x in the atmosphere is thus critical to understanding the production of elevated levels of ozone and the photooxidant chemistry that determines oxidizing capacity and thus atmospheric residence times.

This need for an improved understanding of the chemistry and climatology of oxidant formation led to the development of the Program for Research on Oxidants: PHotochemistry, Emissions and Transport (PROPHET). With an initial focus on the photochemical and transport processes responsible for the formation of ozone at a rural site in the upper Midwest, PROPHET seeks to quantify the impact of Midwestern industrial and biogenic emissions on oxidant production and distribution, and to improve our understanding of the chemistry, partitioning, and fate of atmospheric nitrogen in this temperate forest region. Because of the directional dependence of NO emissions sources, and the variability of the flow regimes between anthropogenic emission impacted and clean northwesterly flow, the PROPHET research site at the University of Michigan Biological Station is an ideal site at which to investigate both the NO_x-dependence of oxidant chemistry, and the impact of biogenic VOCs.

Efforts associated with this initial focus include continuous measurements of O₃, carbon monoxide (CO), ultraviolet radiation, and meteorological parameters, seasonal intensives when simultaneous measurements of reactive oxidized nitrogen species, volatile hydrocarbons, oxidants, and aerosols are added, and measurements of CO₂, H₂O, and isoprene, fluxes. Seasonal Intensives were held in Summer 1997, Fall 1997, Winter 1998, and Summer 1998, 2000, and 2001. Results of the PROPHET Summer 1998 intensive were published in as special section in the 27 October 2001 issue of Volume 106 of the Journal of Geophysical Research Ð Atmospheres.

While the general aims of PROPHET have focused on improving our understanding of gas-phase and heterogeneous oxidant chemistry, we are also interested in studying the exchange of gases and particulate matter between the biosphere and the atmosphere and in better understanding how forest-atmosphere interactions influence the composition of the atmosphere and atmospheric variables influence forest ecosystems. It is well known that nitrogen is a critically important nutrient to plants. However, the relative role of atmospheric deposition as a source of biologically active nitrogen and the importance of individual atmospheric nitrogen compounds are poorly defined. As well, the fate of deposited nitrogen and the extent to which it influences rates of photosynthesis, and thus carbon uptake and storage, and the deleterious effects of deposition of phytotoxic compounds such as O₃ and peroxyacetyl nitrate on nitrogen and carbon uptake are not well understood. This expanded focus on the Biospheric Exchange of Atmospheric Carbon and Odd Nitrogen (BEACON) includes measurements of isoprene, ozone and reactive, oxidized nitrogen species fluxes as well as studies of direct foliar uptake of nitrogen species and effects of ozone deposition.

The Carroll research group is focusing on measurements of ambient levels and fluxes of O₃, NO, NO₂, and total reactive nitrogen, NOy. Measurements are obtained using custom designed and constructed chemiluminescence instruments, and efforts include instrument optimization and characterization, field measurements, as well as data analysis involving trajectory and photochemical modeling.

REPRESENTATIVE PUBLICATIONS

1. Carroll, Mary Anne, and Anne M. Thompson, "NO_x in the Non-Urban Troposphere", invited, in "Progress and Problems in Atmospheric Chemistry", Edited by John R. Barker, Advanced Series in Physical Chemistry - Vol. 3, 198 - 255. World Scientific Publishing Company, Singapore, 1995.
2. Duderstadt, K. A., M. A. Carroll, S. Sillman, T. Wang, G. Albercook, L. Feng, D. D. Parrish, J. S. Holloway, F. C. Fehsenfeld, D. R. Blake, N. J. Blake, and G. Forbes, Photochemical ozone production and loss rates at Sable Island, Nova Scotia, during the North Atlantic Regional Experiment 1993 Summer Intensive, J. Geophys. Res., 103, 13531-13555, 1998.
3. Carroll, M. A. , P. B. Shepson, S. B. Bertman, Overview of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET) Summer 1998 Measurements Intensive, J. Geophys. Res., 106, 24,275-24,288, 2001.
4. Thornberry, T. D., M. A. Carroll, G. J. Keeler, S. Sillman, M. P. Witmer-Rich, M. S. Town, S. B. Bertman, M. R. Pippin, K. Ostling, S. Bird, J. W. Grossenbacher, P. B. Shepson, W. R. Stockwell, O. R. Cooper, and J. L. Moody, Observations of Reactive Nitrogen Oxides and Speciation of Total NOy during the PROPHET 1998 Summer Intensive, J. Geophys. Res., 106, 24,359-24,386, 2001.
5. Pippin, M. R., S. Bertman, T. Thornberry, M. Town, M. A. Carroll, and S. Sillman, Seasonal Variations of PAN, PPN, O3, and CO at the upper Midwest PROPHET Site, J. Geophys. Res., 106, 24,451-24,463, 2001.