Database Status

AirData reports and maps use data extracted from two EPA databases, identified below. This page gives the date when we last obtained data from those databases, and the approximate schedule of the updates.

Air Monitoring Data

EPA Database	Air Quality System (AQS)
Type of Air Pollutant	Criteria	Hazardous
Data Extraction Schedule	Monthly, usually by the 5-th day	Quarterly, usually by the 5-th day
Last AirData Update	14 January 2009	14 January 2009
Data Years Available	1998 - 2008

The AQS database is updated daily, primarily by the staff of state and local environmental agencies that measure ambient concentrations of criteria air pollutants at several thousand monitoring sites in all states and territories. Each month, we extract a summary of the measurements recorded at each air monitoring station -- the highest value in a year, the average, etc. -- and update AirData.

We extract measurements of hazardous air pollutants quarterly (January, April, July, October) rather than monthly. State and local environmental agencies must send air samples for laboratory analysis to determine the concentration of hazardous air pollutants, so AQS database updates generally are less frequent than for criteria air pollutants.

Emissions Data - Criteria Air Pollutants

EPA Database	National Emission Inventory (NEI)
Data Extraction Schedule	Every 3 years
Last AirData Update	4 November 2008
Data Years Available	Point Sources: 1990, 1996, 1999, 2002 County Totals: 1990, 1996 - 2002

EPA compiles a national inventory of criteria air pollutant emission sources every three years, and uses that information to update the NEI database. We update AirData after each national inventory is completed.

Because of changes in EPA emission inventory procedures, emissions for year 1999 and after may not be directly comparable with prior years, especially with regard to particulate matter emissions. Some facility IDs and names changed in the 1999 data, and it may not be possible to identify unambiguously the corresponding facilities in data for earlier years.

Emissions Data - Hazardous Air Pollutants

EPA Database	National Emission Inventory (NEI)
Data Extraction Schedule	Every 3 years
Last AirData Update	4 November 2008
Data Years Available	1999, 2002

EPA compiles a national inventory of hazardous air pollutant emission sources every three years, and uses that information to update the NEI database. We update AirData after each national inventory is completed.