The ABC’s of air pollution
PRIMARY AIR POLLUTANTS
These pollutants are emitted directly into the air from various sources. They include:
Nitrogen Oxides (NOx)
When oxygen and nitrogen react at high temperatures, they form nitrogen oxides.
In the northern midlatitudes, fossil fuel combustion dominates the emission of nitrogen oxides, and in the tropics, biomass burning produces the majority of the nitrogen oxides.
In the atmosphere, these nitrogen oxides can react with other chemicals to form ground-level ozone, and nitric acid can contribute to aerosol formation.
Carbon Monoxide (CO)
Incomplete combustion of the carbon in fuel produces this colorless and odorless gas. Even low exposures can aggravate cardiac ailments—high exposures can cause nervous system problems.
Volatile Organic Compounds (VOCs)
Fossil fuel combustion, industrial activities, fires and even plants can emit these compounds.
Long-lived VOCs can contribute to
aerosols, and short-lived VOCs can react with other chemicals to produce ground-level ozone.
Aerosols
The atmosphere contains gases and solid and liquid particles suspended in the air. These particles—typically only a fraction of the width of a human hair—are known as aerosols or particulate matter.
Aerosols are both primary and secondary air pollutants. Winds blowing sea salt, dust and other debris into the atmosphere contribute to the larger aerosols—which are primary air pollutants.
High concentrations of aerosols can cause cardiovascular disease, and the finer particles can be absorbed into the lungs and even sometimes into the bloodstream. Aerosols also contribute to the haze that impairs visibility.
SECONDARY AIR POLLUTANTS
These chemicals are formed through reactions in the atmosphere. They include:
Ground-Level Ozone
When the sun shines on the mix of VOCs and nitrogen oxides, a photochemical cycle forms ozone—a
pernicious air pollutant, toxic to both humans and plants.
Organic Aerosols
Inefficient combustion in cars, wood stoves, agricultural fires and wildfires causes organic aerosols to spew into the air. These organic particles account for one-third of the aerosol mass in the atmosphere.
Location, Location
While ozone at ground level is a pernicious air pollutant, ozone higher up in the atmosphere—in the stratosphere—helps make life on Earth possible for humans. Stratospheric ozone absorbs 99 percent of the sun’s ultraviolet (UV) radiation before it reaches the planet. The remaining UV radiation that reaches the Earth’s surface can damage cells and cause skin cancer and immune-system suppression.
