The EPA’s new standard limits PM2.5, the smallest regulated particles, to 9 micrograms per cubic meter of air. This is the midpoint of a recommended range from the agency’s Clean Air Scientific Advisory Committee and a 25% cut from the prior cap. This new cap is among the toughest in the world.
Although federal standards lump all fine particles together as a single pollutant, they’re more like a stew of ingredients. Some, like sea salt, dust and black carbon, are emitted to the air directly as particles. Others, like sulfate, nitrate and ammonium, start out mainly as gases that interact in the atmosphere to form particles downwind. Organic carbon, the leading type of PM in many regions, originates as both gases and particles that react in complex ways.
Countless natural sources such as trees and soils, and human-made ones such as vehicles, factories and fertilizers, add various mixes of these ingredients to the stew.
The EPA’s new standard limits PM2.5, the smallest regulated particles, to 9 micrograms per cubic meter of air. This is the midpoint of a recommended range from the agency’s Clean Air Scientific Advisory Committee and a 25% cut from the prior cap. This new cap is among the toughest in the world.
Although federal standards lump all fine particles together as a single pollutant, they’re more like a stew of ingredients. Some, like sea salt, dust and black carbon, are emitted to the air directly as particles. Others, like sulfate, nitrate and ammonium, start out mainly as gases that interact in the atmosphere to form particles downwind. Organic carbon, the leading type of PM in many regions, originates as both gases and particles that react in complex ways.
Countless natural sources such as trees and soils, and human-made ones such as vehicles, factories and fertilizers, add various mixes of these ingredients to the stew.
Fine particulates (red dots) are 2.5 microns in diameter – far smaller than the width of a human hair.USEPA
States operate more than 1,000 monitors that measure the total amount of PM in the air. Unfortunately, only about 150 of those monitors are sophisticated versions called speciation monitors that measure what the PM is made of – information that’s critical for developing effective controls. Thousands of counties don’t even have a total PM monitor, despite satellite evidence showing that many would exceed the new standard.
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