2001: Mapping Urban Aerosols and Emissions to Study Climate and the Environment

Anthropogenic impacts on air quality and the atmosphere are projected to have serious health consequences (such as pollution and thinning of the ozone layer) as well as climate impacts ( such as global warming). In the long run, these human-induced changes will diminish the capacity of the Earth to sustain life, and will therefore have serious detrimental impacts on sustained development. Forecasting air quality and atmospheric impacts requires development of models based on sound scientific theory and robust and relevant observations.

One of the important anthropogenic factors is the production of aerosols. Aerosols are suspended solid and liquid particles in the atmosphere. There are both natural and man-made sources of aerosols. Aerosols are recognized as being one of the greatest sources of uncertainty in understanding long-term climate change due to their direct effect on the radiation budget which is predominantly caused by scattering, or absorption, of short wavelength solar radiation before it reaches the surface of the Earth. Aerosols also have an indirect impact on the Earth's radiation budget by modifying cloud properties through changes in the size and concentration of cloud droplets. These changes occur because aerosols provide central cores onto which water vapor can condense. Aerosols also play an important role in atmospheric chemistry by providing surfaces where chemical reactions can take place.

Besides the obvious need for accurate aerosol measurements for climatological modeling, surface aerosols represent a serious health concerns because of their impact on air quality (e.g. as possible causes of respiratory problems) and are considered one of the most serious air pollutants.

Finally, aerosols also play a confounding role in the remote sensing of the surface of the Earth from airborne and satellite instruments. Unlike cloud cover which generally obscures land features, the effect of aerosols on remote sensing is more invidious, because they reduce the contrast between bright and dark surfaces and can potentially mix, or blur, the signals from pixels that are near one another. Moreover, these effect are highly variable because they are dependent on the microstructure and amount of aerosols present. The CCNY ICP team will be studying aerosol loading in our region using data from Multi-Filter Rotating Shadowband Radiometers and CIMEL sunphotometers at CCNY, GISS, Medgar Evers College, Stevens Institute of Technology, Lamont Earth Observatory. Measurements from these instruments can be processed to obtain the total optical depth at several wavelengths. The total optical depth can then be analyzed to obtain aerosol optical depth and its spectral variation providing an indication of the column loading and size of the aerosols.

The goal of this research study is to map the aerosol optical depth over an urban area (New York City) using observations from several sites. Besides the sites mentioned above, measurements will be made in the Bronx, and Long Island as well.

The particular questions that will guide our research include:

1. Is the aerosol optical depth uniform or irregular over New York area?
2. If not, can the variations be understood in the light of local geography?
3. Are variations correlated with local aerosol sources (power plants, incinerators)? Can the variations be explained by local, or large-scale, meteorological patterns?
4. Does the pattern of aerosol optical depth remain consistent from day to day? Is the gradient in optical depths between areas constant day-to-day?

As part of this work, we will develop an understanding of the reliability and robustness of data quality from the instruments, as well as an understanding of the regression methods used for estimation of optical depth including techniques to eliminate outliers in the data. Lidar data from CCNY will be used to provide information on the vertical variation of aerosol concentration. This information can be used to provide a quantitative link between aerosol optical depth measurements and the visibility measurements that are made by meteorologists.