Wood Smoke Emissions

What is Wood Smoke?

Wood smoke air pollution from wood burning is a carcinogen that comprises a mixture of solids, gases and liquids.

Wood smoke includes over 200 chemicals and compounds that are health and environmental hazards including pollutants as follows:

  • Particulate Matter (PM) – a mixture of solid and liquid particles that are categorized as coarse, fine and ultrafine (particles). Microscopic PM that is 2.5 microns in diameter (PM2.5) and 30 times smaller than the human hair is the signature most damaging pollutant in wood smoke emissions and a carcinogen.
  • Carbon Monoxide (CO) – a toxic, odorless, colorless gas.
  • Volatile Organic Compounds (VOCs) i.e. evaporated carbon compounds that usually have no color, taste or smell including benzene, formaldehyde and benzo-a-pyrene (a polycyclic aromatic hydrocarbon (PAH)) which react with NOx in sunlight to form ozone (photochemical smog) Some of these gases are carcinogens, including benzene and formaldehyde.
  • Nitrogen Dioxide (NO2) – a toxic reddish-brown gas, that contributes to particle pollution and combines with VOCs to make ozone and with water vapor to form acid rain or acid fog.
  • Sulfur Dioxide (SO2) – an inorganic compound, heavy, colorless, poisonous gas that has a strong, unpleasant smell that can react with other compounds in the atmosphere to form particulate matter (PM) pollution.
  • Dioxins – a group of highly toxic chemically-related compounds that are persistent organic pollutants (POPs) i.e., any of several persistent toxic heterocyclic hydrocarbons.
  • Lead (Pb) – a heavy metal toxic to humans.
  • Carbon Dioxide (CO2) and Methane (CH4) – two pollutants that contribute to adverse health effects and climate change by increasing the natural concentration of carbon dioxide and methane in the atmosphere, amplifying Earth’s natural greenhouse effect.

Toxic wood smoke and second-hand wood smoke are similar to toxic cigarette smoke and second-hand cigarette smoke in terms of their pollutant components. In communities like Allegheny County where residential wood burning is common, wood smoke can be responsible for as much as 20% of the airborne particulate matter, and a lesser percent of the VOCs and CO in the air. We discuss health effects as to wood smoke on the next page – Wood Smoke Health Effects under the Basics tab.

What Standards Apply to Wood Smoke Pollutants?

The Clean Air Act (see Options page under the Law tab) mandates EPA to identify and maintain the National Ambient Air Quality Standards (NAAQS) for air quality. The NAAQS specifies 1) concentrations for pollutants that are proven to damage property and to harm human health (primary standards) and 2) concentrations for those pollutants that are proven to cause environmental damage (secondary standards). The current NAAQS comprise six key pollutants or “criteria” pollutants – all but one of which are components of wood smoke:

  • Carbon Monoxide
  • Lead
  • Nitrogen Oxides
  • Particulate Matter (PM)
  • PM10 – Any particulate matter with a diameter less than or equal to 10 microns
  • PM2.5 – Any particulate matter with a diameter less than or equal to 2.5 microns. Also called “fine particulate matter.”
  • Ozone
  • Sulfur Dioxide

The standards set forth allowable pollutant concentrations (units of measure for the standards are in parts per million (ppm) by volume, parts per billion (ppb) by volume, and micrograms per cubic meter of air (µg/m3) for each “criteria” pollutant as follows.

Table courtesy of: https://www.epa.gov/criteria-air-pollutants/naaqs-table

How Do You Assess and Measure Wood Smoke?

You can assess or measure wood smoke air pollutant emissions objectively or subjectively in terms of the allowable concentrations as per the above standards; in terms of the legally allowable spread and visibility or visible emissions (smoke); and in terms of the legally allowable odor or malodorous matter emissions. These assessments or measurements along with common law remedies e.g., negligence, nuisance, and trespass are generally the basis for determination of compliance as to wood smoke related issues. A discussion of applicable law as to wood smoke is on the Options page under the Laws tab. The following is a summarization of the physical measurement of the signature pollutant PM2.5, as well as the assessment or measurement of wood smoke visibility or visible emissions and the assessment or measurement of odor or malodorous matter emissions. The associated pages under the Observations tab detail these efforts.

For more detailed information as to smoke chemistry and chemical composition and the properties of wood smoke go to:




How Do You Measure Particulate Emissions from Wood Smoke?

Particulate or Particulate Matter (PM) emissions also known as particle pollution is a mix of solids and liquid droplets suspended in air. This pollution includes components such as acids (nitrates and sulfates), organic chemicals, metals, soil or dust particles, and allergens (e.g., fragments of pollen or mold spores). One may view particulate emissions as either Primary or Secondary. Primary PM emissions are emitted directly into the air, secondary PM emissions are formed in the air by the chemical reactions of gaseous pollutants.

Using particulate sensors/monitors, one can measure wood smoke particulate air pollution emissions in terms of particle size and concentration ((particles/.01 cubic feet) or mass concentration (ug/m3)) as per the above standards. Stricter limits notwithstanding, PM2.5 is reported as in violation of the standards when it exceeds the 24-hour standard of 35 μg/m3 (EPA) or 25 μg/m3 (WHO). However, PM2.5 is reported as a health concern when it reaches just 12.1 μg/m3 as per the Air Quality Index (AQI). The Wood Smoke Health Effects page under the Wood Smoke Basics tab relates in some detail the health effects of PM2.5 at different levels of air quality.

PM2.5 presents the greatest wood smoke health risk, because it can penetrate deeply into the lungs, and thence the bloodstream, the circulatory system and almost all organs. Studies link PM2.5 exposure – short and long term – to an array of serious respiratory, cardiovascular, neurological and other health issues.

The Wood Smoke Health Effects page under the Basics tab sheds light on the adverse health and environmental effects of wood smoke. Specific guidance as to the observation of particulate matter (PM2.5) emissions from wood smoke in terms of monitoring (the actual measurement of emission levels), recording (the readings), and formally reporting (the results) is set forth under the Observations tab.

For more information as to wood smoke particulate emissions and PM2.5 visit:









How Do You Assess or Measure Visible Emissions from Wood Smoke?

One can subjectively assess visible emissions from wood smoke in terms of its offensive and objectionable nature and visible spread (across property boundaries). One can also measure the visible emissions of wood smoke objectively in terms of “opacity”. Opacity is the percentage reduction in the transmission of light or obscureness of the view of an object in the background due to the emission of air contaminants. Generally (barring other criteria or stricter limits), smoke, if any, is reported as excessive under the law when it obscures the view of objects behind it by more than 20%. High opacity is an indication of possible health effects due to pollutant levels e.g., particulate matter (PM2.5) in the air.

The higher the opacity, the worse air quality becomes.

Combustion efficiency, combustion temperature, wood moisture content, airflow, size of the fire, type (age and condition as applicable) of facility, and type of wood all affect the offensive and objectionable nature and spread, and opacity of wood smoke.

Specific guidance as to the observation of the visible emissions of wood smoke as to monitoring, recording, and formally reporting results is set forth under the Observations tab.

To more fully appreciate the importance of visible emissions visit:





How Do Ypou Assess or Measure Odor/Malodorous Matter Emissions from Wood Smoke?

You can subjectively assess odor as to wood smoke in terms of its offensive and objectionable nature i.e., its frequency, duration and perceived strength and dispersion (across property boundaries). You can also measure malodorous matter emissions objectively in terms of its physically detected strength i.e., its D/T “Dilution-to-Threshold” ratio. The “Dilution-to-Threshold” ratio is a measure of the number of dilutions needed to make odorous ambient air “non-detectable” using a field olfactometer such as the Nasal Ranger pictured below. The olfactometer creates a calibrated series of discrete dilutions by mixing the odorous ambient air with odor-free (carbon) filtered air. More stringent limits notwithstanding, strength levels exceeding a D/T of 7 in the ambient air could be considered non-compliant under a community’s prevailing rules and regulations.

Odor or malodorous matter emissions are in general a complex mixture of chemicals, many times they have a very low odor “threshold” i.e. parts per billion (ppb). So odor or malodorous material can be one key indicator of possible health effects – physical and mental – as well as non-specific symptoms and sickness such as headaches, depression, etc. At the Observation tab you can access an excellent dialog as to odor assessment or malodorous emissions’ monitoring, recording and reporting.

Specific guidance as to the observation of wood smoke odor/malodorous matter emissions in terms of monitoring (the actual assessment and/or measurement of emission levels), recording (of observations/readings), and formally reporting (results) is set forth under the Observations tab.

The following expand on the assessment, measurement, nature and consequences of odor or malodorous emissions:



“Odor Basics”, Understanding and Using Odor Testing

Authored by:

Charles M. McGinley, P.E.

St. Croix Sensory, Inc.

Michael A. McGinley, MHS

St. Croix Sensory, Inc.

Donna L. McGinley

St. Croix Sensory, Inc.

Presented at

The 22nd Annual Hawaii Water Environment Association Conference

Honolulu, Hawaii: 6-7 June 2000


“Taking a Look Beyond Odor”

SWANA – Landfill Gas Symposium – New Orleans, Louisiana, March 16-19, 2015 ALS Environmental Air Quality Laboratory, 2655 Park Center Drive, Simi Valley, CA St. Croix Sensory, 1150 Stillwater Blvd N, Stillwater, MN

Principal Contact: Samantha Henningsen, Project Manager, ALS Environmental Air Quality Laboratory, 2655 Park Center Drive, Simi Valley, CA 93065, (805) 526-7161 samantha.henningsen@alsglobal.com

“The “Gray Line” Between Odor Nuisance and Health Effects”

Michael A. McGinley, MHS

St. Croix Sensory, Inc.

Charles M. McGinley, P.E.

McGinley Associates, P.A.