Air Emissions from Chemical Plants

What are some major air pollutants associated with an ethane cracker?

Ozone

Petrochemical industrial processes do not directly create ground-level ozone. It is a secondary pollutant, created by reactions between the volatile organic compounds released by industry and ambient oxygen compounds such as nitrogen oxides. These reactions must occur in the presence of sunlight to create ozone. For this reason, ground level ozone tends to be most prevalent on hot, sunny days. The EPA has named ground-level ozone as one of the six most common pollutants.

Exposure to ozone can result in acute chest pain or sore throat, and even lung inflammation and damage in vulnerable populations such as children and asthmatics.  Though urban environments tend to have higher amounts of ground level ozone, it can be transported by the wind to rural environments as well.

VOCs (Ethylene and Propylene):

Volatile Organic Compounds (VOCs) are highly reactive chemical compounds released from industrial processes, consumer solvents, and motor vehicles. In the presence of sunlight, VOCs react with oxygen and nitrogen oxides, which are commonly created by combustion of fossil fuels to form ozone. Exposure to VOCs and ozone has been associated with increased rates of asthma, lung and respiratory infections, and cardiovascular problems.

In the case of petrochemical production, two common and highly reactive VOCs are ethylene and propylene. A 2010 study found these compounds were two of the largest contributors to ozone production in the Houston, TX area.

Exposure to ethylene via ethylene oxide can result in central nervous system depression and irritation of eyes, nose, and other mucous membranes. The EPA classifies it as a probable human carcinogen. Propylene oxide has similar effects to those of ethylene oxide, and can also cause skin irritation if dermal contact occurs via liquid solution. Though direct exposure to these compounds is deleterious to human health, exposure to high enough levels to cause sickness is rare. 

Hazardous Air Pollutants

HAPs, also known as toxic air pollutants are a class of regulated air pollutants that can cause cancer and other human health problems. They are present in industrial releases of refineries and chemical plants, including ethane crackers, though the amounts of emissions vary by plant type. 

Benzene 

Benzene is an ubiquitous substance in the production of petrochemicals. Both an intermediary and an end-product, benzene is made of six hydrogen molecules and six carbon molecules. It has been recognized as a human carcinogen.  Exposure to benzene may occur through inhalation near industrial facilities, like petrochemicals plants, that use it in their processing. Since it is also a major component of gasoline, inhalation is possible at gas stations, as well as from cigarette smoking.

Some immediate signs of high blood levels of benzene include drowsiness, dizziness, and confusion. Aside from cancer, long term exposure to benzene may result in irregular menses in women, anemia, and immunosuppression.

1,3-Butadiene

1,3-Butadiene is another hydrocarbon used in the petrochemical industry, usually to make synthetic rubber, plastics, and copolymers such as acrylics. Like benzene, 1,3-Butadiene is known as a human carcinogen, however lower level exposures are also associated with mucous membrane irritation, neurological effects, low blood cell count, and lymphatic system effects. Additionally, it is suspected to have negative effects on pregnant mothers and their unborn children.

-Jill Terner contributed to this report.