Air Quality Atlas

The Air Quality Atlas is a collection of maps prepared by the Air Quality
Analysis Section in the Region 6 office of the U.S. Environmental Protection
Agency (EPA). The atlas presents a spatial analysis of air quality in EPA
Region 6 for 1996, focusing on the six criteria pollutants for which the EPA
has set primary and secondary standards to protect public health and welfare.
These standards, defined as the National Ambient Air Quality Standards (NAAQS),
have been set for the following six pollutants: lead, nitrogen dioxide, carbon
monoxide, sulfur dioxide, ozone, and small particles less than or equal to 10
microns in aerodynamic diameter (PM-10). The primary standards are set to
protect public health, and the secondary standards are set to protect public
welfare, such as buildings, forests, and agricultural crops. The primary and
secondary standards are currently identical for all of the criteria pollutants
except sulfur dioxide. The sulfur dioxide secondary standard is based on a
three hour averaging time, while the primary standard is based on both 24-hour
and annual averaging times.

The maps show Region 6 air quality levels referenced against the standards set
for the six criteria pollutants. The legend for each map, except for the two
exceedance day maps, was constructed to show the following information: (1) The
blue shade depicts levels less than 10% of the standard; (2) the green shade
depicts levels between 10-50% of the standard; (3) the gray shade depicts
levels between 50-90% of the standard; (4) the yellow shade depicts levels
within 10% of the standard; and (5) the red shade depicts levels over the
standard. Counties not shaded (white) either do not contain monitors, or their
monitors did not achieve a data capture rate of at least 75% (exception - all
ozone site data were reported). The data used to compose each map were obtained
from the EPA's Aerometric Information Retrieval System (AIRS) data base.

Analysis of the maps reveals that all Region 6 monitors recorded concentrations
below the NAAQS set for lead, nitrogen dioxide, and sulfur dioxide. Indeed, a
significant amount of areas in Region 6 recorded maximum concentrations well
below these standards. Additional map analysis shows that one Region 6 county
(El Paso) contained monitors recording measurements above the carbon monoxide
8-hour standard, that two Region 6 counties (El Paso and Dona Ana) contained
monitors recording measurements above the PM-10 standards, and that every state
except Arkansas had at least one monitor with values above the ozone standard.
Following each map displaying the 1996 Region 6 status of particulate and ozone
air quality is a map showing the number of days per county in which a monitor
recorded concentrations above the PM-10 or ozone standards.

[Summary provided by the EPA.]