Heterogeneous Chemistry

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Heterogeneous Chemistry

As particles are transported through the atmosphere their chemical composition and size change as they become mixed with other particles, undergo cloud or fog processing, and react with trace gaseous pollutants. This last process, the reaction of gases with a particle's surface, is a heterogeneous reaction. Such reactions alter the chemical composition of the atmosphere by shifting soluble species such as acids and ammonia from the gas to particulate-phase (gas-to-particle conversion). This changes both the chemical balance of the atmosphere and the chemical composition of the particles, thus altering their physical and chemical properties, and how the particles behave in the atmosphere.

The temporal changes in the chemical composition of single particles can be observed by ATOFMS and provides unique and important insights into the heterogeneous chemistry that particles undergo during atmospheric transport. An example is shown below from the ACE-Asia campaign when a major Asian dust storm subsided to sea level, passing through the polluted boundary layer, before being analysed by the ATOFMS. Large temporal changes in the relative amounts of sulfate, nitrate, and chloride in the dust particles, caused by these heterogeneous reactions, are evident.

We also use ATOFMS to prove the kinetics and mechanisms of heterogeneous reactions in controlled laboratory studies to understand these ambient observations. A schematic of the aerosol kinetics flow tube that we have built to study this chemistry is shown below. We are currently focused on the heterogeneous chemistry of mineral dust and sea salt particles in a polluted marine boundary layer, and how these two particle types compete for reaction with various gases such as SO2, HNO3, and HCl.

Figure 2. Temporal evolution of secondary species in Asian mineral dust sampled aboard the R/V

Ronald Brown. Hourly averaged single-particle peak area ratios (lines) from all filtered dust

particles for four major secondary species: NH₄⁺ (m/z = 18/m/z = 27), Cl⁻ (m/z = −35/ m/z = 27),

NO₃⁻ (m/z = −62/m/z = 27), and HSO₄⁻ (m/z = −97/m/z = 27). Total hourly ATOFMS dust particle

counts (bars) are also displayed. Time periods corresponding to different air mass source

regions as described by Bates et al. (2004) are indicated. All times are in UTC.

Flow Tube Diagram

Related references:

Guazzotti, S.A., R.C. Sullivan, D.A. Sodeman, Y.H. Tang, G.R. Carmichael, and K.A. Prather, Mineral dust is a sink for chlorine in the marine boundary layer, Proceedings of the National Academy of Sciences of the United States of America (Submitted), 2006.

Sullivan, R.C., S.A. Guazzotti, D.A. Sodeman, and K.A. Prather, Direct observations of the atmospheric processing of Asian mineral dust, Atmospheric Chemistry and Physics Discussions, 6, 4109-4170, 2006.

Arimoto, R., Y.J. Kim, Y.P. Kim, P.K. Quinn, T.S. Bates, T.L. Anderson, S. Gong, I. Uno, M. Chin, B.J. Huebert, A.D. Clarke, Y. Shinozuka, R.J. Weber, J.R. Anderson, S.A. Guazzotti, R.C. Sullivan, D.A. Sodeman, K.A. Prather, and I.N. Sokolik, Characterization of Asian Dust during ACE-Asia, Global and Planetary Change, 52, 23-56, 2006.

Whiteaker, J.R., and K.A. Prather, Hydroxymethanesulfonate as a tracer for fog processing of individual aerosol particles, Atmospheric Environment, 37 (8), 1033-1043, 2003.

Whiteaker, J.R., D.T. Suess, and K.A. Prather, Effects of meteorological conditions on aerosol composition and mixing state in Bakersfield, CA, Environmental Science & Technology, 36 (11), 2345-2353, 2002.

Angelino, S., D.T. Suess, and K.A. Prather, Formation of aerosol particles from reactions of secondary and tertiary alkylamines: Characterization by aerosol time-of-flight mass spectrometry, Environmental Science & Technology, 35 (15), 3130-3138, 2001.

Hughes, L.S., J.O. Allen, P. Bhave, M.J. Kleeman, G.R. Cass, D.Y. Liu, D.F. Fergenson, B.D. Morrical, and K.A. Prather, Evolution of atmospheric particles along trajectories crossing the Los Angeles basin, Environmental Science & Technology, 34 (15), 3058-3068, 2000.

Liu, D.Y., K.A. Prather, and S.V. Hering, Variations in the size and chemical composition of nitrate-containing particles in Riverside, CA, Aerosol Science And Technology, 33 (1-2), 71-86, 2000.

Gard, E.E., M.J. Kleeman, D.S. Gross, L.S. Hughes, J.O. Allen, B.D. Morrical, D.P. Fergenson, T. Dienes, M.E. Galli, R.J. Johnson, G.R. Cass, and K.A. Prather, Direct observation of heterogeneous chemistry in the atmosphere, Science, 279 (5354), 1184-1187, 1998.

Page developed by Ryan Sullivan and Andy Ault

Last Updated 7/5/2006