The NAQSAT allows input and provides “Effectiveness Results” for the following constituents of potential concern.
Odor: Odors from livestock farms can be made up of hundreds of compounds (odorants). How these odorants interact with one another contributes to the specific character of an odor. Odorous compounds tend to be carried on dust particles, and, therefore, strategies to reduce odors from animal agriculture often include strategies to reduce dust.
Particulate matter (PM): Particulate matter, or dust, varies in size on the basis of source and formation. The primary concerns related to airborne particles are haze/visibility and health effects. Dust emitted from farms is highly complex in size, physical properties and composition. For regulatory purposes, airborne particulates are commonly classified into PM10 (≤10 µm in aerodynamic diameter) and PM2.5 (≤2.5 µm in aerodynamic diameter). Coarse particles (2.5 to10 µm in diameter) tend to be deposited in the upper airways of the respiratory tract; fine particles (PM2.5) can reach and be deposited in the smallest airways (alveoli) in the lungs. Farms can contribute coarse particles directly through animal activity, feed preparation, animal housing ventilation units and vehicular traffic. They can also contribute fine particles as the result of a secondary formation process (gas-to-particle conversion; see section on ammonia).
Ammonia: Ammonia is a colorless, pungent, nitrogenous gas. It volatilizes from a solid or liquid material when the ammonium ion is present and other physical conditions exist. Ammonia gas can react in the atmosphere with gaseous acidic species to form fine particulates (ammonium [NH4+] aerosols), which are a health concern.
Atmospheric NH3 can be deposited during rain events and lead to soil acidification and increased concentrations of nitrogen in surface waters, potentially contributing to eutrophication.
Hydrogen sulfide: Hydrogen sulfide is a colorless, pungent gas best known for its characteristic rotten-egg odor. At high concentrations, hydrogen sulfide can be toxic (silo gas), and even at low concentrations it is a respiratory irritant. Although hydrogen sulfide is not transported great distances, at the farm it can mix with other compounds to contribute to odor.
Methane: Methane is a greenhouse gas. It is a natural product of decomposition of organic materials in the absence of oxygen (anaerobic). Sources of methane include landfills, anaerobic manure storages and the rumens of dairy and beef animals (enteric emissions). Methane can be collected and used as an energy source (biogas for compressed gas fuel or electrical generation through a genset engine).
Volatile organic compounds (VOCs): VOCs are a large group of organic chemicals that include an atom of carbon (excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate) and that participate in atmospheric photochemical reactions. Some of these reactions may lead to increased concentration of tropospheric ozone (a criteria pollutant) at ground level, thereby contributing to levels exceeding the National Ambient Air Quality Standard. VOCs can be odorous or contribute to farm odor.