Research
Aerosol Measurements on the Hudson River
Aerosols are tiny, airborne particles that range from millimeters to thousandths of a millimeter in diameter. In the atmosphere, aerosols form visible air pollution or haze and can substantially reduce visibility even on cloudless days.
Aerosols are either emitted directly into the air from a variety of anthropogenic (human) and natural sources or are the end product of chemical reactions in the atmosphere. For example aerosols are released whenever something is burned, whether by humans or as a result of a natural event such as a forest fire sparked by lightening. Sea spray injects salt particles into the atmosphere which can then be transported hundred of miles inland. Trees also emit gases that can form organic particulates in the air when they react under sunlight. Aerosols also affect regional and local climate by reducing the amount of solar energy that reaches the surface of the Earth and by playing a role in cloud formation.
Multi-filter rotating shadowband radiometer at Lamont-Doherty that measures the optical properties of aerosols in the atmosphere over the Hudson River.
Photo by Beate Liepert
In addition to making direct measurements of aerosols by filtering particles out of the air, airborne particles can be analyzed by examining their optical properties. Aerosols scatter and absorb sunlight in specific ways based on their chemical makeup and size and in proportion to their concentration in the atmosphere. Instruments like the one on the roof of the Oceanography Building at the Lamont-Doherty Earth Observatory (see photo) measure the way that aerosols . Because this instrument is similar to ones on satellites, it is also used by NASA to ground truth satellite data.
Lamont-Doherty is an ideal site for measuring anthropogenic aerosols because the atmosphere in both locations is influenced by four major sources: cars and households in the New York City metropolitan area, the coast and other local natural fluxes of sea salt, forests, and pollution from Midwestern power plants and more distant sources. Aerosol concentrations strongly depend on variables such as wind direction, humidity, temperature and cloud cover, so meteorological parameters are also measured on-site.