Benzene concentrations continue to be above the ambient air guideline during the winter.
Benzene is a carcinogen which is present in liquid fuels such as gasoline, diesel and aviation fuels and is emitted through evaporation as well as released by the combustion of carbonaceous materials, including fossil fuels and biomass. Tobacco smoke contains benzene and accounts for nearly half the national exposure to benzene. The bottom chart below illustrates data, from the US EPA 2011 National Emissions Inventory database, that states approximately 95% of benzene emissions are generated from mobile or non-point sources - see EPA's definitions below. The ambient air guideline is the recommended chemical concentration in ambient air below which there is minimal risk of a deleterious health effect resulting from long-term inhalation exposure to benzene. Note that concentrations are frequently above the ambient air guideline during the winter.
Description of U.S. EPA 2011 National Emissions Inventory Data Categories
The NEI Point data category contains emissions estimates for sources that are individually inventoried and usually located at a fixed, stationary location, although portable sources such as some asphalt or rock crushing operations are also included. Point sources include large industrial facilities and electric power plants, but also increasingly include many smaller industrial and commercial facilities, such as dry cleaners and gas stations, which had traditionally been included in Nonpoint sources. The choice of whether these smaller sources are estimated individually and included as point sources or inventoried as a Nonpoint source County or Tribal area aggregate is determined by the separate State, Local, or Tribal air agency.
The NEI Nonpoint data category contains emissions estimates for sources which individually are too small in magnitude or too numerous to inventory as individual point sources, and which can often be estimated more accurately as a single aggregate source for a County or Tribal area. Examples are residential heating and consumer solvent use.
The NEI Onroad and Nonroad data categories contain mobile sources which are estimated for the 2011 NEI v1 via the MOVES2010b and NONROAD models, respectively. NONROAD was run within the National Mobile Inventory Model (NMIM). Note that emissions data for aircraft, locomotives, and commercial marine vessels are not included in the Nonroad data category starting with the 2008 NEI. Aircraft engine emissions occurring during Landing and Takeoff operations and the Ground Support Equipment and Auxiliary Power Units associated with the aircraft are included in the point data category at individual airports. Emissions from locomotives that occur at rail yards are also included in the point data category. In-flight aircraft emissions, locomotive emissions outside of the rail yards, and commercial marine vessel emissions (both underway and port emissions) are included in the NonPoint data category.
Nonroad mobile sources:
Mobile sources not found on roads and highways (e.g., airplanes, trains, lawn mowers, construction vehicles, farm machinery).
Onroad mobile sources:
Vehicles found on roads and highways (e.g., cars, trucks, buses).
The Events data category includes wildfires, wild land fire use and prescribed burns. Wild land fire use is controlling a wildfire to use as a prescribed burn. This web page provides emissions for this data category as county totals. Day-specific and fire-specific emissions are available on the Emissions Modeling Clearinghouse with the 2011 emissions platform data.
Contact: Rich Greves 207-287-7030