By 2010, major air pollution reduction
programs will be implemented and major reductions are anticipated.
As these programs take effect, greater emphasis will be placed
on tracking compliance and progress towards meeting health and
environmental goals. If compliance and progress are not sufficient,
the EPA may propose to take additional emission reduction actions
to meet these goals. However, such "linear" thinking
may not solve the problem of standard compliance.
A large-scale, real-life experiment
has begun. The "piston" effect,
as described elsewhere on the web pages, will make it difficult
to attain the 0.08 ppm 8-hour ozone standard. in many areas in
the United States. With the reduction of the 0.08 ppm 8-hour
standard to 0.075 ppm, even greater difficulty will arise in
attaining the 8-hour form of the standard. The piston effect
says that as ozone control strategies are implemented, the hourly
distribution of ozone concentrations will not decrease uniformly,
with the higher concentrations decreasing faster than the midrange
concentrations. The result of the "piston"
effect is that as new control strategies are implemented, the
states and the U.S. EPA will see some progress in the reduction
of hourly average ozone concentrations at sites that experience
0.10 ppm and above. These reductions will translate into lower
4th highest seasonal 8-hour daily maximum concentrations. As
the states and the EPA continue to strive for further reductions
in the 8-hour average concentrations by attempting to reduce
the hourly average concentrations below 0.09 ppm, because of
the "piston" effect, progress will begin to slow down
at an alarming pace. Soon the EPA and the states will notice
that the implemented control strategies are not working as effectively
as originally predicted and will conclude erroneously that more
stringent local controls will be needed. In some locations, the
8-hour standard will be attained for specific years but in other
years, the 8-hour standard may be violated at the same location.
As the years go by, an oscillation in and out of violation will
occur. Please visit our concerns web
page to follow the progress made in meeting the 8-hour standard.
On that page, please note the decrease of the trending in the
8-hour ozone concentrations nationwide in the shorter trending
period compared to the longer trending period.
Research reported in the literature has
described the problems in reducing hourly concentrations of ozone.
Lefohn et al. (1998) identified those sites that demonstrated
a significant reduction in ozone levels for the period 1980-1995.
Using the data from the sites that experienced reduced ozone
levels over the period of time, the authors investigated whether
the rate of decline of the mid-level hourly average concentrations
was similar to the rate experienced by the high hourly average
concentrations. The analysis indicated that there is a greater
resistance to reducing the hourly average concentrations in the
mid range than the hourly average concentrations above 0.09 ppm.
Figure 1 below is an example that shows that the higher hourly
average concentrations (i.e., above 90 ppb) decreased at a faster
rate (greater negative rate per year) than the hourly average
concentrations in the mid-level range. The numbers of hourly
average concentrations in the low end of the distribution also
decreased. Both the high and low ends of the distribution moved
toward the center of the distribution.
Figure 1
Lefohn et al. (1998) discussed the movement
of the low hourly average ozone concentrations toward the mid-level
values (i.e., the decrease of the frequency of the lower hourly
average concentrations). Figure 2 illustrates the frequency of
occurrence
Figure 2
of hourly average ozone concentrations
at two monitoring sites. The Custer National Forest site in Montana
experiences very low maximum hourly average concentrations. The
distribution of the hourly average concentrations at the site
shows a lack of both high and low hourly average concentrations.
The number of lower hourly average concentrations is reduced
because of a lack of NOx scavenging. As reductions in emissions
occur, the shift from the lower hourly average concentrations
to mid-level values is expected to occur. For 1980, more than
10% of the hourly average and 8-hour daily maximum concentrations
at the site were above 0.05 and 0.059 ppm, respectively. The
hourly and 8-hour daily maximum concentrations above 0.05 ppm
at this site may not be associated with long-range transport
of ozone and its precursors from more polluted locations. The
site experienced its highest hourly average concentrations in
April and May; this is when most sites in the United States do
not experience high hourly average average concentrations. This,
coupled with the observation that the diurnal maximum concentrations
occurred between 1400 and 1500 local time, implies that the ozone
may have been generated locally or meteorological processes are
transporting the ozone down from aloft. The sources for creating
the ozone may have been natural.
The distribution pattern of the hourly
average concentrations for a heavily urban-influenced monitoring
site at Jefferson County, Kentucky is shown in Figure 2. In contrast
to the rural site in Montana, the urban-influenced site in Kentucky
showed frequent high and low hourly average concentrations. This
site appeared to be influenced by NOx scavenging because of the
occurrence of more frequent low hourly average concentrations.
Lefohn et al. (1998) reported in their
trends analyses, that as ozone levels improved for several urban
sites, both the high and the low hourly average concentrations
moved toward the 0.03-0.06 ppm range, which is within the range
of concentrations that most frequently occurred at the rural
site in Montana. Lefohn et al. (1998) hypothesized that as adequate
control strategies were implemented, the distribution pattern
of hourly average concentrations for inland monitoring sites
would approach the pattern observed at the Montana site and other
remote sites in the western United States.
Coyle, Fowler, and Ashmore (2003) have
reported for an analysis of United Kingdom monitoring data that
peak ozone concentrations declined by about 30% over the past
decade, but that there was evidence of an increase in annual
mean concentrations of about 0.1 ppb per year. Using simulation
modeling, the authors reported that the lower concentrations
increased. Although the authors hypothesize that this increase
may reflect the impact of global increases in background concentrations,
such may not be the case. The most current EPA Ozone Criteria
Document (2006) notes that that
there has been an increase in O3 concentrations at the lower
levels throughout the monitoring period, which is consistent
with data obtained in Europe, showing that O3 minima increased
during the 1990s because of reduced titration of O3 by reaction
with NO in response to reductions in NOx emissions.
As noted above, Lefohn et al. (1998) reported
decreases in the frequency of the lowest ozone concentrations
and increases in the mid-level concentrations and believed that
the decreases in frequency at the lower concentrations were due
to reduced NOx scavenging. In addition, as noted elsewhere
on this web page, no changes have been observed in the 4th
highest 8-hour concentration at some remote and relatively remote
clean national park sites in the United States. Published work
by Oltmans et al. (2006) indicates that relatively remote clean
monitoring sites in national parks in the western United States
have not shown indications of ozone trending.
The "piston" effect is real and
it appears that the implementation of politically acceptable
control strategies may never be able to allow many violating
areas to reach attainment on a continuous basis. Some
nonattainment areas will continue to oscillate into and out of
violation. Nature has provided us with the "piston"
effect and the challenge is how best to work with it. Researchers
have begun to better understand the physical processes that are
at work (Reynolds et al., 2003; 2004).
In assessing the efficacy of air pollution
reduction programs, it is important to determine whether 1) expected
emission reductions have occurred, 2) actual emission changes
resulted in changes in ambient concentrations consistent with
the predictions of air quality models, 3) changes in ambient
concentrations have resulted in reductions in human and ecosystem
exposure to the air pollutants in question, and 4) reductions
have led to improved public health and reduced damage to sensitive
ecosystems. If inconsistent observations are found to occur,
then it is quite possible that there were problems with the assumptions
used in the development of the current 8-hour standard. If so,
it will be necessary to assess the physical, biological, and
mathematical methodologies used to develop the ozone standard
prior to reaching the simple conclusion that more emission reductions
are needed. It is important to learn from past mistakes instead
of ignoring them.
As indicated by Lefohn et al. (1998), the
selection of the current form of the 8-hour standard will not
allow us to deal properly with the "piston" effect.
Observe the "piston" effect at work at a Fairfield,
Connecticut ozone monitoring site for the period 1980-2007.
Note that it is harder to decrease the 4th highest value of the
8-hour standard the lower the value. This is an example of the
"piston" effect. The answer may lie not in more
stringent emission controls, but in changing the form of the
8-hour average standard to one that will provide for the same
amount of human health protection and yet be attainable.
A.S.L. & Associates is actively performing research in this
area with several key investigators.
References
Coyle M., Fowler, D. and
Ashmore M. (2003) New Directions: Implications of Increasing
Tropospheric Background Ozone Concentrations for Vegetation.
Atmospheric Environment. 37:153-154.
Lefohn A. S., Shadwick
D. S. and Ziman S. D. (1998) The Difficult Challenge of Attaining
EPA's New Ozone Standard. Environmental Science & Technology.
32(11):276A-282A.
Oltmans S. J., Lefohn A.
S., Harris J. M., Galbally I., Scheel H. E., Bodeker G., Brunke
E., Claude H., Tarasick D., Johnson B.J., Simmonds P., Shadwick
D., Anlauf K., Hayden K., Schmidlin F., Fujimoto T., Akagi K.,
Meyer C., Nichol S., Davies J., Redondas A., and Cuevas E. (2006)
Long-term changes in tropospheric ozone. Atmospheric Environment.
40:3156-3173.
Reynolds, S. D.; Blanchard, C. L.; Ziman,
S. D. (2003) Understanding the effectiveness of precursor reductions
in lowering 8-hr ozone concentrations. J. Air & Waste Manage.
Assoc. 53: 195-205.
Reynolds, S. D.; Blanchard, C. L.; Ziman,
S. D. (2004) Understanding the effectiveness of precursor reductions
in lowering 8-hr ozone concentrations - Part II. The Eastern
United States. J. Air & Waste Manage. Assoc. 54: 1452-1470.
U.S. Environmental
Protection Agency (2006) Air Quality Criteria for Ozone and Related
Photochemical Oxidants. Research Triangle Park, NC: Office of
Research and Development; report no. EPA/600/R-05/004af.
