Our research on atmospheric chemistry problems aims at exploring the fundamental processes that govern the concentrations and distributions of trace gases. The findings will help unravel some aspects of the complicated relations between the changing environment and human activities. Traditionally, atmospheric chemistry research includes three categories, laboratory, field experiment, and modeling. Our colleagues at Tech are among the leading experts in these areas. Our work generally falls into the third category. Modeling is merely a way of analyzing field observations and testing scientific hypotheses. Our research could be divided into two areas depending on the complexity of the models used.

Data analysis and 0-1 D modeling

Data analysis is fundamentally a reduction process. Field observations are complex. However, the tenet of science holds that the underlying principals that generated the complex phenomena are "simple". In data analysis, we look for these "simplicities".

Modeling can be described as a method of data analysis. The models can be either constructed from scientific principals or of empirical nature. Factor analysis is the latter type. We have applied positive matrix factorization (PMF) and principal component analysis (PCA) methods to analyze the major air masses that contribute to the observed variability and seasonal trends of O₃ during the TOPSE experiment. The chemical characteristics of the air masses reflect emission sources they encountered and can be evaluated with backtrajectory analysis. Please follow this link to a  more detailed description.

Point (0-D) model is built with our current understanding of photochemical reactions. It captures the complexity of  photochemical interactions. The models are generally constrained by the observed concentrations of some (long-lived) species. The model predictions of the other (generally shorter-lived) species can be compared to the observations. Disagreement between simulated and observed concentrations may signal problems in our current understanding of photochemistry and points to the need for laboratory studies. Key factors influencing the concentrations of O₃, HO_x, NO_x, and other important species are diagnosed. Please follow this link to a more detailed description of our analysis of the TOPSE data.

The 1-D model captures the transport processes in addition to photochemical reactions in the 0-D model. Photochemistry changes more rapidly with altitude in part to the the rapid change of photon availability, temperature, and water vapor. The vertical advection in the atmosphere is much slower than horizontal advection Convective and turbulent processes are critical in vertical transport. The tropical troposphere exemplifies the importance of convective transport on chemical distributions. We used CH₃Cl as a tracer for the amount of tropical convective transport during PEM-Tropics A and B. Please follow this link to a more detailed description of our analyses.

Regional and global 3-D models

The 3-D models attempt to simulate the interaction between photochemistry and dynamic transport. The processes include emissions, transport, photochemistry, and deposition. As a result, they are computationally expensive.

The regional 3-D modeling system includes two models, the NCAR/Penn State MM5 and a regional chemistry and transport model. For high latitude simulations, the polar version of MM5 is used. We are applying this modeling system to three analyses, (1)  TOPSE observations at mid and high latitudes, (2) the effects of frontal lifting and cumulus convection on export of pollutant from the US in April, 2000, and (3) modeling and forecast support for the ANTCI experiment (a more comprehensive experiment following ISCAT) over Antarctic. Please follow this link to a more detailed description. In summer 2003, we plan to conduct 48-hour forecasts of O₃ and its precursors over the U.S. You can find our forecasts here.

The global model is described in great detail in the GEOS-CHEM web site. It is an "off-line" chemistry and transport model. The assimilated meteorological fields are provided by the Goddard Earth Observing System (GEOS) of the NASA Global Modeling Assimilation Office. We are applying the GEOS-CHEM model to simulate the global distribution of CH₃Cl and CH₂O. In the latter work, GOME observations of CH2O are provided by Dr. Kelly Chance at the Harvard Smithsonian Astrophysical Observatory. We also collaborate in this work with Drs. Randall Martin (Dalhousie University), Paul Palmer (Harvard University), and Daniel Jacob (Harvard University). Please follow this link to a more detailed description. Some early global 3-D modeling work can be found here.