HAP benefits 

Due to data, resource, and methodology limitations, we were unable to estimate the 

benefits associated with the 1,014 tons of hazardous air pollutants that would be reduced as a 

result of this rule. Available emissions data show that several different HAPs are emitted from 

stationary engines, either contained within the fuel burned or formed during the combustion 

process. The HAPs measured in emission tests conducted on diesel fired stationary RICE 

include 1,3-butadiene, acetaldehyde, acrolein, benzene, ethylbenzene, formaldehyde, n-hexane, 

naphthalene, polycyclic aromatic hydrocarbons (PAHs), polycyclic organic matter, styrene, 

toluene, and xylene. Metallic HAPs from diesel fired stationary RICE that have been measured 

include cadmium, chromium, lead, manganese, mercury, nickel, and selenium. 

Although numerous HAPs may be emitted from RICE, a few HAPs account for 80% of 

the total mass of HAPs emissions from diesel stationary RICE. These HAPs are formaldehyde 

(25%), acetaldehyde (19%), PAH (18%), naphthalene (9%), and acrolein (9%). 

• Formaldehyde is the HAP emitted in the largest quantities from stationary RICE. 

Acute and chronic exposures to formaldehyde may irritate the eyes, nose, and 

throat, and may cause coughing, chest pains, and bronchitis. Reproductive 

effects, such as menstrual disorders and pregnancy problems, have been reported 

in female workers exposed to formaldehyde. Limited human studies have 

reported associations between formaldehyde exposure and lung cancer, 

nasopharyngeal cancer, and possibly leukemia. Animal inhalation studies have 

reported an increased incidence of nasal squamous cell cancer. EPA classifies 

formaldehyde a probable human carcinogen.1

 

• Acute exposure to acetaldehyde may result in irritation of the eyes, skin, and 

respiratory tract. In humans, symptoms of chronic exposure to acetaldehyde 

resemble those of alcoholism. Long-term inhalation exposure studies in animals 

have reported damage to the nasal epithelium and mucous membranes, growth 

retardation, and increased kidney weight. EPA has classified acetaldehyde as a 

probable human carcinogen based on nasal tumors in rats and laryngeal tumors in 

hamsters.2

 

 

1

 Summarized from EPA’s Health Effects Notebook. Available on the Internet at 

http://www.epa.gov/ttn/atw/hlthef/formalde.html 2

 Summarized from EPA’s Health Effects Notebook. Available on the Internet at 

http://www.epa.gov/ttn/atw/hlthef/acetalde.html 
• Polycyclic aromatic hydrocarbons (PAHs) are a broad class of compounds whose 

molecules are composed of fused aromatic carbon rings, and whose toxicity varies 

widely depending on molecular structure. Dermal exposures to environmental 

mixtures of PAHs cause skin disorders in humans and animals. An increase in 

lung cancer has been reported in humans exposed to PAH-bearing mixtures 

including coke oven emissions, roofing tar emissions, and cigarette smoke. 

Animal studies have reported respiratory tract tumors from inhalation exposure to 

one PAH compound, benzo[a]pyrene. The EPA has classified seven PAH 

compounds as probable human carcinogens.3 

• Acute exposure to naphthalene can cause hemolytic anemia (with symptoms of 

fatigue, lack of appetite, restlessness, and pale skin) as well as nausea, vomiting, 

diarrhea, blood in the urine, and a yellow color to the skin. Chronic exposure to 

naphthalene has been reported to cause cataracts and damage to the retina. EPA 

has classified naphthalene as a Group C, possible human carcinogen.4

• Acute inhalation exposure to acrolein may result in upper respiratory tract 

irritation and congestion. The major effects from chronic (long term) inhalation 

exposure to acrolein in humans consist of general respiratory congestion and eye, 

nose, and throat irritation. Acrolein is a strong dermal irritant, causing skin burns 

in humans. Data are not adequate for an assessment of the human carcinogenic 

potential of acrolein.5 

The distance that these HAPs travel away from the emission source depends on several 

factors. HAPs such as formaldehyde, acetaldehyde, PAHs, and acrolein are emitted as gases. 

Regional photochemical model simulations have shown that gaseous HAPs like formaldehyde 

and acetaldehyde can be transported hundreds of kilometers from their emissions source in 

distinct plumes (U.S. EPA, 2010b). Further, these emissions can contribute to regional airmasses 

with elevated concentrations of gaseous HAPs. These polluted airmasses can be transported 

thousands of kilometers and affect locations well distant from the original emissions source. 

Some gaseous HAPs transform into particles in the atmosphere. For HAPs emitted as particles, 

such as metals, the travel distance primarily depends on the size of the particle and 

meteorological conditions, such as wind speed and precipitation. Fine particles can have an 

 

3

 Summarized from EPA’s Health Effects Notebook. Available on the Internet at 

http://www.epa.gov/ttn/atw/hlthef/polycycl.html 4

 Summarized from EPA’s Health Effects Notebook. Available on the Internet at 

http://www.epa.gov/ttn/atw/hlthef/naphthal.html 5

 Summarized from EPA’s Health Effects Notebook. Available on the Internet at 

http://www.epa.gov/ttn/atw/hlthef/acrolein.html 
atmospheric half-life of days to weeks and travel hundreds to thousands of kilometers, whereas 

ultrafine and coarse particles travel less than ten kilometers (U.S. EPA, 2009c).