January-February 1997 Tiny parts have large role in pollution On some clear, cloudless days over the Chesapeake, it is impossible to see from one side to the other because the air is packed with so many microscopic particles that they block the view.
Sulfur dioxide is converted into sulfate particles, and it gets real hazy.
But tiny particles also pose problems to the Chesapeake that are less visible to the naked eye. Deposition from the air is one of the leading sources of nutrient and toxic pollution to the Chesapeake and much of that pollution, particularly toxics, reaches the Bay in the form of particulates. The EPA currently regulates particulate matter in the atmosphere of 10 microns or less to no more than 150 micrograms per cubic meter on a daily basis, and no more than 50 micrograms per cubic meter as an annual average. Based on evidence that smaller particles pose a larger human health risk because they can be inhaled deeper into the lungs, the EPA is now proposing a more strict standard. It would limit smaller particles, of 2.5 microns or less, to concentrations of 50 micrograms per cubic meter daily and an average of 15 micrograms per cubic meter annually.