Dr. Aslam Khalil

Professor, Department of Physics
Portland State University

Science Building II, Room 410
(503) 725-8396 (office)
(503) 725-8550 (fax)

E-mail: aslamk@odin.pdx.edu

B.Phys., Physics, B.A., Mathematics, B.A., Psychology, University of Minnesota, Minneapolis 1970; M.S., Physics, Virginia Polytechnic Institute, 1972; Ph.D., Physics, Center for Particle Theory, University of Texas, Austin, 1976; M.S., Environ. Sci., Oregon Graduate Center, 1979; Ph.D., Environmental Science, Oregon Graduate Center, 1979.

Undergraduate Assistant, Department of Mathematics and Department of Physics, Univ. Of Minnesota, 1968-1970; Teaching Assistant. VPI, 1970-1971; Graduate Assistant, Department of Mathematics and Department of Physics, University of Texas, 1971-1972; Teaching Assistant, Univ. of Texas, 1972-1973, 1976; Research Scientist Assistant, Center for Particle Theory, Univ. of Texas, 1972-1976; Instructor, Department of Physics, Pacific University, 1978; Research Assistant, OGC, 1977-1979; Senior Research Associate, OGC, 1979-1980; Assistant Professor, Department of Environmental Science, OGC, 1980-1982; Associate Professor 1982-1984; Professor, Department of Environmental Science and Engineering, OGI, 1984 - 1995; Director, Center for Global Change, OGI, 1991 - 1995; Professor, Department of Physics, PSU, 1995 - present.

Editor, Chemosphere:Global Change Science (Elsevier Press, Oxford, England); Editorial Board member, Handbook of Environmental Chemistry, Environmental Science and Pollution Research International, Atmospheric Environment.

Research Interests

DR. ASLAM KHALIL is a theoretician with diverse research interests. He directs the Global Change Research Program at Portland State, a group of scientists conducting research on areas ranging from the sources and characteristics of urban air pollution to the long-term global effects of man-made pollutants. During the last decade, Dr. Khalil has published more than 180 papers dealing with a wide spectrum of subjects related to global change science. The work has laid the foundations for understanding how and why the atmosphere is changing and what global climatic changes may occur if these trends continue. The following are some highlights of the work.

A program was begun around 1979 to systematically study the trace gas composition of the earth's atmosphere. Based on the global atmospheric circulation patterns, six sites were chosen to sample the atmosphere. These sites, representing polar, middle and tropical latitudes of both hemispheres, are still in operation and constitute a unique source of information on the trends and distributions of man-made and natural trace gases. The analysis and interpretation of this data has included the application of modern statistical methods and the development of 1-, 2-, and low resolution 3-dimensional global chemical tracer models.

Data from this network established for the first time the world-wide increasing trends of methane, carbon monoxide, molecular hydrogen and several exotic man-made chlorofluorocarbons and bromine-containing gases.

Data on methylchloroform (CH3CCl3) was used to estimate the global concentration of tropospheric OH radicals, the most significant oxidant in the global atmosphere. These methods are now being used to evaluate possible trends of OH based on the decade of methylchloroform measurements and to test the idea that the oxidizing capacity of earth's atmosphere is being reduced by human activities.

Dr. Khalil, in collaboration with Dr. Reinhold Rasmussen, maintains a very active research program on the methane cycle, and first showed that methane was increasing in the atmosphere. The main results of this work are:

  1. A robust global budget of methane was constructed that has stood the test of time for over a decade. It was the first budget based on theoretical constraints on the global sources derived from experimental data, specifically on the average OH concentrations deduced from CH3CCI3 measurements.
  2. Based on ice core data, further theoretical constraints were developed on the role of human activities in changing the atmospheric concentrations of methane (and nitrous oxide).
  3. Based on agricultural and other records, the emissions of methane were estimated over the years of the last century. The results show a dramatic increase in emissions controlled by human activities (cattle, rice agriculture, natural gas use, landfills). The trends of anthropogenic emissions are slowing down in this decade (M.A.K. Khalil and M.Shearer).
  4. Over the last 10 years, the trends published by various groups have varied from 2%/yr to less than 0.8%/yr. Drs. Khalil and Rasmussen found that the trends of methane have varied considerably over the last decade. When this variation is taken into account, all the studies agree. The trend was higher in the early 1980s and is lower now. This result is explained by the declining trends of emissions, which are related to the "limits of growth" already affecting agricultural sources.
  5. Drs. Khalil and Rasmussen are active in estimating the fluxes of methane from emissions from various sources, including termite mounds in Australia and rice fields in China.

On a regional scale, Drs. Khalil and Rasmussen were the first to use gases as signatures of the origins and the nature of Arctic haze. These studies supported most of the results that had been obtained from the chemical analysis of the Arctic aerosol and have established gas phase atmospheric chemistry as a valuable tool for understanding sources of regional scale pollution.

Finally, on even smaller scales, CH3Cl was used as a unique tracer of wood smoke. Using a chemical mass balance model, they were able to quantitatively estimate the contribution of wood burning to air pollution. In later studies, the approach was extended to estimating the contributions of various sources to urban carbon monoxide concentrations. These studies have extended the applicability of chemical mass balance models, which previously relied entirely on the chemical composition of the pollution aerosol.

In addition to these sustaining areas of research, Dr. Khalil and his group embarked on an holistic program to study global change. The main components of this program are:

  1. Analysis of global patterns of gases from "campaign experiments". Such experiments are highly focused on specific ecosystems and their role in atmospheric chemistry. The design and analysis of these experiments is especially complicated. The group has pioneered the application of cluster analysis and non-parametric statistical methods to obtain robust results from these experiments, particularly when only sparse data are obtained. Such experiments have been carried out in Brazil, China, Antarctica, Australia, the Arctic, various parts of the United States and from long transacts on ships and aircraft.
  2. A detailed photochemical model of tropospheric OH has been developed. This model is used to study the spatial and seasonal variations of the losses of CH4 and CO, which react with OH.
  3. The OH model and results from analysis of polar ice cores have been used to study photochemistry in the pre-industrial atmospheres, inter-glacial periods, ice ages and modern times. A remarkable result that has emerged is that concentrations of OH are stabilized during widely varying climatic conditions by compensation between processes that reduce OH and those that increase OH (M.A.K. Khalil and J.P. Pinto).
  4. A 1-dimensional radiative-convective time-dependent climate model has been developed. The model has been expanded to 2-dimensions and tied to the 2-D tracer circulation model to study feedbacks between climate and the global methane cycle (R.M. MacKay and M.A.K. Khalil).

Selected Publications

Non-CO2 greenhouse gases in the atmosphere.
M.A.K. Khalil. Annual Review of Energy/Environment, Annual Reviews, 1999, Vol. 24: 245-261, 1999.

Earth’s atmosphere.
M.A.K. Khalil. Encyclopedia of Geochemistry, Encyclopedia of Earth Sciences Series, C.P. Marshall and R.W. Fairbridge, Editors, Kluwer Academic Publishers, p. 143-145, 1999.

Measurements of methane emissions from rice fields in China. 
M.A.K. Khalil, R.A. Rasmussen, M.J. Shearer, R.W. Dalluge, L.X. Ren, and C.-L. Duan, J. Geophys. Res., 103(D19): 25,181-25,210, 1998.

Emissions of methane, nitrous oxide, and other trace gases from rice fields in China. 
M.A.K. Khalil, R.A. Rasmussen, M.J. Shearer, Z.-L. Chen, H. Yao, and Y. Jun, J. Geophys. Res., 103(D19): 25,241-25,250, 1998.

Atmospheric methane over the last century.
M.A.K. Khalil, M.J. Shearer, and R.A.Rasmussen, World Resource Review, 8(4): 481-492, 1996.

The distribution of solar radiation in the Earth’s atmosphere: The effects of ozone, aerosols, and clouds.
Y. Lu and M.A.K. Khalil. Chemosphere, 32(4): 739-758, 1996.

Greenhouse gases in the earth’s atmosphere.
M.A.K. Khalil. Encyclopedia of Environmental Biology, Volume 2, W.A. Nirenberg, Editor, Academic Press, Florida, p. 251-265, 1995.

The global sources of nitrous oxide.
M.A.K. Khalil and R.A. Rasmussen; J. Geophys. Res., 97(D13):14651-14660, 1992.

Theory and development of a one-dimensional time-dependent radiative convective climate model.
R.M. MacKay and M.A.K. Khalil, Chemosphere, 22(3-4):383-417, 1991.

Linear least squares method for time series analysis with an application to a methane time series.
M. A. K. Khalil and F. P. Moraes. Journal of the Air and Waste Management Association, 45, Jan 1995.

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