Strategic Assessment of Florida's Environment
(SAFE)
Nitrogen Dioxide Emissions and Exceedances
Explanation of Indicator
The gaseous oxides of nitrogen (NOx) normally found in
the
atmosphere include nitrous oxide, nitric oxide, and
nitrogen
dioxide. Nitric oxide is a precursor to the
formation of
nitrogen dioxide (NO2) and an active compound in ozone
formation.
Globally, emissions of nitrogen oxides from natural sources
are
almost 10 times greater than emissions from man-made
sources.
However, man-made sources are of greater importance in
the
occurrence of nitrogen dioxide and ozone air pollution
because
they are concentrated in populated areas. A major man-
made
source of nitrogen oxide emissions is fuel combustion in
motor
vehicles. The other major source is electric power plants.
In
the atmosphere, nitric oxide is oxidized to nitrogen dioxide
at a
rate dependent on the ambient concentrations of nitric oxide
and
ozone. Although the rate is enhanced by ozone, it only
requires
oxygen. This indicator measures the nitrogen dioxide
emissions
from permitted stationary print sources and mobile sources
based
on vehicle miles traveled data and the average emission
factor
obtained from the USEPA MOBILE5a model. The average
emission
factor varies according to vehicle speeds, local
meteorology, the
type and model year mix of vehicles, and the year of
the
analysis. In 1994, the nitrogen dioxide monitoring
network in
Florida consisted of ten monitoring stations in eight
counties.
The Florida ambient standard is 100 ug/m3, an annual
average
based on the arithmetic mean.
Nitrogen dioxide (NO2) is a pulmonary irritant
affecting
primarily the upper respiratory tract. Of greater
concern is
nitrogen dioxide's contribution to the formation of ozone
which
poses the far greater health hazard. In addition,
nitrogen
dioxide combines with the moisture in the air to form weak
nitric
acid, an important constituent of acid rain. Acid rain has
been
found to increase the susceptibility of aquatic and
terrestrial
ecosystems to various forms of environmental stress.
Source
Ambient monitoring data can be obtained from Bill Davis,
Bureau
of Air Monitoring and Assessment, FDEP, 2600 Blair Stone
Road, MS
5510, Tallahassee, Florida 32399-2400, or at (904) 488-
6140.
Permitted facilities emissions data is from Tom Rogers,
Office of
Policy and Program Management, FDEP, 2600 Blair Stone
Road, MS
5500, Tallahassee, Florida 32399-2400, or at (904) 488-
0114.
Mobile source emissions data is reported in the State
Highway
System Mileage Report, obtained from the
Transportation
Statistics Office, FDOT, 605 Suwannee Street,
Tallahassee,
Florida 32399-0450, (904) 488-4111. Data can also be
obtained
from the Mobile Source Control Section, Bureau of Air
Monitoring
and Mobile Sources, FDEP, 2600 Blair Stone Road, MS
5510,
Tallahassee, Florida 32399-2400, (904) 488-6140.
Data Characteristics
Information is summarized annually statewide, on a county
basis,
since 1980. It is available in hard copy format for
retrieval
and printout costs. Monitoring data is available in
summary
format at no charge.
Overall Assessment
Emissions data generally have good data quantity and
quality.
About half of NOx emissions come from the large utility
power
plants and the remainder from mobile sources. The plants
usually
provide better than average data. These same plants
will be
required to directly measure NOx emissions in the
future,
providing even more accurate data. Emissions are
usually
calculated indirectly using general emission factors and
source
activity data. Thus, the emissions data are limited by
the
accuracy of these factors and activity information.
Most of
these data are minimally quality controlled. Small,
unpermitted
sources are not accounted for, but they represent a very
small
fraction of the total emissions. High emissions of NO2 are
not
always indicative of high concentrations in the area. Nor
are
low emissions indicative of low concentrations. The
emission
characteristics of the source (stack height, gas
exit
temperature, etc.) play an important role in the
dispersion of
the pollutant. Although monitored data is based on
information
from a limited number of sites, this indicator still serves
as a
direct measure of air pollution concentrations at the
monitoring
station locations. This indicator is limited to counties
that
have air quality monitoring programs. In addition, monitors
are
not equally likely to record a number of exceedances due to
the
fact that all monitors are not sited using identical
siting
criteria.
Analysis of Indicator
From 1980 through 1993, there have been no exceedances of
the
ambient standard for nitrogen dioxide. However, since
1985,
nitrogen dioxide emissions from permitted facilities in the
state
have fluctuated. From 1985 to 1988, there was an increase
of 13
percent. There was an 8.2 percent increase in emissions
from
1988 to 1990. The overall increase over the eight year
period of
record was 38.5 percent. The eight year average is 360,671
tons
per year.
While there has never been an exceedance of the nitrogen
dioxide
standard in the state, the levels of NO2 are of interest
because
of their contribution to ozone formation. The graphs below
show
that the NOx emissions from stationary sources have risen
more
than emissions from mobile sources. Stationary source
emissions
are usually emitted from smoke stacks. Mobile sources, on
the
other hand, generate their emissions near the surface and
are not
as readily dispersed.
NOx emissions from vehicles may more readily become trapped
and
convert to ozone. Nitrogen oxides, as a precursor to
ozone, is
receiving increasing attention by regulators and policy
makers in
efforts to curtail the formation of ozone.
Nitrogen Dioxide Emissions From Permitted
Facilities
Nitrogen Dioxide Emissions From Mobile Sources
