Irritant Gases & Fine Particulate Pollution

Exponent's multidisciplinary team has training and experience to assist with the investigation of the potential toxicity of suspected sources of irritant gas and/or fine particulate exposures. Our Certified Industrial Hygienists sample bulk materials, surfaces, water, or air for evidence of problematic agents. Our process engineers and air dispersion modelers evaluate the pathways and potential magnitude of chemical or dust exposures. Exponent’s toxicologists, epidemiologists, and physicians that interpret the findings with respect to human health hazards and evaluate evidence of disease causation from chemical or dust exposures.

What are Irritant Gases and Why are They Important?

Irritant gases are chemicals capable of causing inflammation of the mucous membranes of the eyes, nose, throat, and lungs at relatively low concentrations, and in some cases, may also cause possible effects on nerves (i.e., sensory irritants). Examples of common irritant gases are ammonia, chlorine, formaldehyde, hydrogen sulfide (and other reduced sulfides), oxides of sulfur or nitrogen, and acid gases. Handling of concentrated forms of chemicals used in food flavorings or fragrance manufacturing can also create exposures to irritant gases, such as concentrated diacetyl, a chemical used to impart a butter-like flavor, or glacial acetic acid, which in dilute form is vinegar. Irritant gases like formaldehyde are often found at higher concentrations indoors due to off-gassing from furniture, flooring, foam insulation, cigarette smoke, and wood-burning fireplaces.

Due to the presence of many different irritant gases in the indoor and outdoor environments from background manmade and natural sources, it can be difficult to discern which agents and/or emission sources might be most important in contributing to annoying odors, reversible irritation or allergic responses, or more serious and/or permanent health outcomes. Moreover, health assessments for each of these constituents must distinguish exposures along this dose-response continuum that might result in negligible to serious health effects.

Fine Particulate Pollution

‘Fine particulate pollution’ is terminology most commonly used to describe airborne combustion products smaller than 2.5 microns (PM2.5) in diameter that are largely comprised of soot or carbon particles with attached polycyclic aromatic hydrocarbons, metals, and other unburnt residues. Examples include vehicle exhaust, fire smoke, and emissions from incinerators and power plants. Fine particulate pollution is a key component of visible smog that occurs in densely populated metropolitan and industrial zones like Los Angeles and Beijing.

Irritant gases and fine particulate pollution together make up the complex mixture of outdoor air pollution that has been associated with short-term irritation of the eyes, nose, throat and lungs in addition to exacerbation of asthma, other lung diseases, and possible neurological and cardiovascular effects. The capability of irritant gases or fine particulate pollution to cause permanent injury to the respiratory tract derives from the specific physical and chemical properties of the material (e.g., water solubility, reactivity, chemical structure) as well as from environmental factors (e.g., humidity, air exchange, temperature) and individual factors (e.g., allergic sensitivity, asthma or other lung disease). Due to the presence of many candidate chemicals and particulate compounds that are commonly involved in potential health effects from occupational or environmental exposures, rigorous scientific analysis is often required to sort out the most likely contributors in the disease causation analysis.

Exponent Publications Related to Irritant Gases

The following are example publications by Exponent staff relating to investigation of irritant gases, fine particulates, and associated diseases:

Boffetta P, La Vecchia C, Moolgavkar S. Chronic effects of air pollution are probably overestimated. Risk Anal 2015; 35:766-769.


Crump, KS, Van Landingham C, Moolgavkar, SH, McClellan, R. Reanalysis of the DEMS nested case-control study of lung cancer and diesel exhaust: suitability for quantitative risk assessment. Risk Anal 2015; 35:676-700.

Fedoruk, MJ and Kerger, BD. Ammonia exposure and hazard assessment for selected household cleaning product uses. J. Expos. Anal. Environ. Epidemiol. 2005; 15:534-544.

Fedoruk, MJ, and Kerger, BD. Measurement of volatile organic compounds inside automobiles. J. Expos. Anal. Environ. Epidemiol. 2003; 13:31-41.

Kerger, BD and Fedoruk, MJ. Pathology, toxicology and latency of irritant gases known to cause bronchiolitis obliterans disease: does diacetyl fit the pattern? Toxicology Reports 2015; (in press).

Kerger BD, Bernal AJ, Scott P. Tissue dose modeling and bronchiolar fibrosis risk for inhalation of highly water soluble irritant gases: Comparison of acetaldehyde, acrolein, and diacetyl. Toxicological Sciences 2015; 142:158. 

Kerger, BD, Thuett, KA, and Finley, BL. 2014. Evaluation of four alpha-diketones for Toll-like receptor 4 (TLR-4) activation in a human transfected cell line. Food Chem. Toxicol. 74: 117-119.

Moolgavkar SH, Chang ET, Luebeck G, Lau EC, Watson HN, Crump KS, Boffetta P, McClellan R. Diesel engine exhaust and lung cancer mortality: time-related factors in exposure and risk. Risk Anal 2015; 35:663-675.

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