State of California
AIR RESOURCES BOARD
Los Angeles Hilton
Golden State Room
930 Wilshire Boulevard
Los Angeles, CA 90017
April 27, 1977
10:00 a.m.
AGENDA
Page
77-8-1 Minutes of the October 4, 1976 Board Meeting.
77-8-2 Public Hearing to Reconsider the California Air 1
Quality Standard for Sulfur Dioxide.
77-8-3 Other Business
a. Executive Session - Personnel & Litigation
b. Research Proposals
ITEM NO.: 77-8-2
Public Hearing to Reconsider the California Air Quality Standard
for Sulfur Dioxide.
RECOMMENDATION
Based on the staff's analysis of the data presented in the
accompanying report and the conclusions set forth below, we make
the following recommendations:
1. That the Board adopt a 24-hour ambient air quality standard
for SO2 at a level of 0.04 ppm;
2. That the Board adopt an additional ambient air quality
standard for SO2, based on a 4-hour averaging period, at a
level of 0.05 ppm; and
3. That the Board, for the interim, retain the currently
accepted measurement methods for SO2 pending the completion
of research studies currently in progress.
SUMMARY
The staff has reviewed a large volume of information pertaining
to SO2 and its effects, much of it published within the past 5
years. A portion of this has been summarized in the accompanying
staff report. The following conclusions represent the results of
our analysis of this information:
1. The federal 24-hour ambient air quality standard for sulfur
dioxide, 0.14 ppm, does not provide adequate health
protection for the vast majority of Californians. The
federal standard does not take into account the known
consequences of interactions of sulfur dioxide with ozone
and other photochemical oxidants in producing or aggravating
disease. It does not adequately consider interactions of
sulfur dioxide with other pollutants, such as nitrogen
oxides and suspended particulate matter, or the suspected
role of SO2 as a cocarcinogen in producing cancer of the
lung. Finally, the federal standard was apparently set
without incorporating a margin of safety. The staff has
concluded that California requires a separate, more
stringent 24-hour ambient air quality standard for SO2.
2. As summarized in Section II. A. of the report, the results
of recent toxicological and epidemiological studies indicate
that simultaneous exposure to sulfur compounds and ozone and
other photochemical oxidants leads to consequences that are
significantly more serious than exposure to either pollutant
alone. This is supported by at least two studies showing
effects at 0.06 ppm SO2 (24-hour average) in the presence of
oxidant at about 0.15 ppm. Many additional studies show
effects in the range of 0.10 to 0.15 ppm SO2 in the presence
of suspended particulate matter.
Since, in the presence of even moderate amounts of oxidant
and suspended particulate matter, effects upon human health
are observed with 24-hour SO2 levels in the range of 0.06 to
0.10 ppm, and since a margin of safety is desirable, the
staff concludes that a 24-hour SO2 standard of approximately
0.04 ppm will provide adequate protection to the health of
essentially all residents in all areas of California.
The proposed 24-hour standard assumes the presence of
photochemical oxidant at ambient levels in excess of the
State 1-hour standard (0.10 ppm) and includes a margin of
safety to ensure adequate health protection for sensitive
groups within the larger population.
3. There is a substantial body of evidence showing that damage
to vegetation occurs at SO2 levels as low as 0.025 to 0.1
ppm (two to eight-hour averages for single and multiple
exposures) and in the presence of oxidants at levels as low
as 0.05 ppm or possibly lower. Since California's prime
agricultural areas frequently experience ambient ozone
levels above 0.10 ppm, the board should assume the presence
of ozone in considering the need for a standard that will
minimize the impact of SO2 on vegetation.
It is also clear that protection of vegetation requires that
special consideration be given to SO2 levels for averaging
periods shorter than 24 hours. Based on the data discussed
in Section II.B. of the report, it appears that a 4-hour
averaging period would be reasonable.
From the brief analysis presented in Section VI of the
report, it appears that a 24-hour standard alone cannot be
expected to provide adequate protection against expected
short-term fluctuations in SO2 levels above levels that are
clearly harmful to vegetation.
On this basis, the staff has concluded that a separate SO2
standard of 0.05 ppm with an averaging time of 4 hours is
desirable to protect vegetation in the presence of
photochemical oxidant at levels above 0.10 ppm.
Even at the level of the proposed 4-hour standard, some
damage to vegetation is expected to occur when moderate
oxidant levels coincide with SO2 concentrations at 0.05 ppm.
However, achievement of this standard will reduce
economically significant damage to an acceptable level and
prevent widespread irreversible damage to forests and to
sensitive ecosystems.
4. A 24-hour SO2 standard of about 0.04 ppm is consistent with
reducing ambient levels of sulfate aerosol to acceptable
levels. The following points are made in support of this:
a. The 0.04 ppm SO2 standard is expected to yield maximum
24-hour sulfate levels of about 22 ug/m3 in the South
Coast Air Basin, consistent with the Board's interim
24-hour sulfate standard of 25 ug/m3.
b. Reduction of sulfate aerosol to approximately these
levels will be required as a part of the broader effort
to meet the State and federal ambient air quality
standards for total suspended particulate matter.
c. Sulfate aerosol contributes substantially to visibility
degradation. No strategy for approaching the
visibility standard can fail to require substantial
reductions in sulfate aerosol. Even at the levels
consistent with the proposed SO2 standard, i.e.,
sulfate levels of 25 ug/m3, sulfate aerosol alone will
account for more than half the total allowable
visibility degradation consistent with the visibility
standard.
5. Many types of materials are damaged after long-term
exposures to ambient levels of SO2. Studies on the exposure
of steels and cotton fabrics to gaseous SO2 show that damage
is linearly proportional to SO2 concentration. Therefore,
the lower the SO2, the less damage incurred. Clearly, a
zero level is desirable, but as a practical matter
protection of materials must be based on economic
consideration. Accordingly, the staff declines to identify
a specific level, and suggests that the Board would be
justified in relying on the standards needed to protect
health and vegetation to provide an acceptable degree of
protection against damage to materials.
6. The staff concludes that none of the measurement methods
currently in use in California for monitoring ambient levels
of SO2 is entirely satisfactory. The ARB staff and EPA
scientists are currently evaluating a "new generation" of
monitoring instruments that promise improved sensitivity and
will be less subject to interferences from other pollutants.
this work is still in progress and the staff is not yet able
to make a final assessment. For the interim, it seams
appropriate to retain the measurement methods currently in
use. Within the next year, a recommendation for adoption of
a new method or methods will be forthcoming, along with
recommendations to establish equivalency with current
methods.
ATTACHMENTS: Resolution - 77-22
Staff Report 77-8-2
Recommendation from the State of California
Department of Health on the Air Quality Standard
for Sulfur Dioxide
STAFF REPORT
Table of Contents
Page No.
I. Introduction 1
II. Effects of Sulfur Dioxide 4
A. Human Health Effects
B. Vegetation Effects 49
C. Effects on Ecosystems
1. Lichens and Bryophytes 128
2. Acid Precipitation 131
D. Effects on Materials 138
III. Sulfate Aerosol Formation 158
IV. Atmospheric Concentrations 173
V. Air Monitoring Measurements 193
VI. Comparability of Air Quality Standards for Different
Averaging Periods 204
VII. Conclusions 209
VIII. Recommendations 217