Environmental Quality Branch
AIR
QUALITY
Air
Quality Report for British Columbia: Ground-Level Ozone
Concentrations (1986-1997)
Last
Updated: July 1998
Executive
Summary
Ground-level
ozone is an important component of urban smog that is
formed from reactions involving nitrogen oxides (NOx)
and volatile organic compounds (VOCs) in the presence
of sunlight. The motor vehicle is a major source of
both NOx and VOCs.
Ozone
is a respiratory irritant, and has been associated with
a decline in lung function and increased hospitalizations
for those with pre-existing respiratory problems. Recent
studies indicate that ozone may be causing health effects,
even at low concentrations. Ozone is also harmful to
plants and to various materials.
Ozone
is currently being monitored at more than 25 sites in
the province. The monitoring network is most dense in
the Lower Fraser Valley (LFV), reflecting both the large
population and the high historical ozone concentrations
found in this region. Data are forwarded to a central
electronic database for storage.
This
report provides an overview of provincial ozone levels
based on data collected between 1986-1997. Data from
19 sites were evaluated. Site selection was based in
part on data availability and on obtaining as broad
a geographical cross section of the province as possible.
Hence, sites with the worst or the best air quality
in the province in any particular year may not have
been considered here. Data from each site were summarized
in a set of summary plots, an example of which is provided
here.
Note: The (larger) graphs below come from page 35 of the full report — Air Quality Report for British Columbia: Ground-Level Ozone Concentrations (1986-1997).
Unless
noted otherwise, analyses were based on hourly ozone
concentrations. The following observations were drawn
from these analyses.
- There
is great temporal and spatial variability in ozone
concentrations measured throughout the province.
- The
highest hourly concentrations were observed during
the summer months, when conditions are most conducive
to ozone formation.
- During
much of the late 1980s, the highest hourly concentrations
were observed at sites immediately downwind of the
most densely populated areas of the LFV, at sites
in Port Coquitlam and Port Moody. Ozone concentrations
were particularly high during the summer of 1988,
when much of North America was under the influence
of a strong high-pressure system that resulted in
extended periods of poor air quality. During this
period, the Port Coquitlam monitoring site recorded
a maximum hourly concentration of 425 µg/m3.
- More
recently, the highest hourly concentrations were recorded
in Hope in 1993 (176 µg/m3), Port
Coquitlam in 1994 (213 µg/m3), Hope
in 1995 and 1996 (188-206 µg/m3),
and Kelowna in 1997 (168 µg/m3).
- On
an annual basis, mean hourly concentrations ranged
from less than 10 µg/m3 to 45 µg/m3.
Over the last five years, the highest mean concentrations
were typically monitored at sites further downwind
of the more densely populated areas of the LFV (e.g.
Surrey, Langley and Hope) and sites outside the LFV
(e.g. Victoria, Kamloops, Kelowna, Williams Lake and
Prince George).
- The
lowest mean concentrations were consistently observed
in Downtown Vancouver (Robson Square), where NOx emissions
from vehicle exhaust are likely responsible for the
destruction of local ozone.
- On
a monthly basis, the highest hourly mean concentrations
were typically observed during the spring months,
particularly during April and May. This finding is
partly attributed to the increased contributions of
stratospheric ozone which occur during the spring,
when the stratosphere is closest to the earth's surface.
The highest concentrations reported during this period
were 60-61 µg/m3 in Kamloops.
- In
contrast, the lowest monthly mean concentrations were
typically observed between November and January. Ozone
concentrations at Vancouver (Robson Square) averaged
less than 10 µg/m3 during this period.
- The
95th percentile concentration, which represents the
level below which 95% of the concentrations fall,
is a useful indicator of long-term trends. Although
very high hourly concentrations were observed in the
late 1980s, a number of sites reported their highest
or second highest 95th percentile and mean concentrations
in 1996. These sites included Vancouver (Robson Square),
Richmond, North Delta, Burnaby (Kensington Park) and
Hope. Data from the Hope site indicates that the annual
mean concentration consistently increased each year
between 1993-96.
- The
national air quality objectives for ozone are currently
under review. The current one-hour maximum acceptable
level is 160 µg/m3. In the late 1980s,
the majority of exceedances of this level occurred
in the Port Coquitlam/North Vancouver/Pitt Meadows
area. More recently, exceedances have also been observed
in Surrey, Langley, Abbotsford, Chilliwack, Hope and
Kelowna.
- In
contrast, no exceedances of the air quality objective
were recorded in Victoria, Squamish, Vancouver (Robson
Square), Kamloops and Prince George between 1986-1997.
However, three of the sites (Victoria, Squamish and
Kamloops) reported hourly concentrations in excess
of 150 µg/m3.
- A
cumulative ozone exposure index, SUM06, was also calculated.
SUM06 values are used to assess the exposure of vegetation
to ozone during the growing season. A value of 11.6
mg/m3-h over a three-month period is expected
to provide protection to 95% of crops. Exceedances
of this level were generally limited to the period
prior to 1989, with the exception of the Hope site,
where exceedances were recorded in 1995 and 1996.
- Hourly
mean, 95th percentile and maximum concentrations observed
at various sites in the province in 1997 were compared.
Based on this combination of parameters, the highest
concentrations were reported for sites in Kelowna
and Kamloops. This finding indicates that these sites
experience both a high background concentration of
ozone throughout the year, and periods of elevated
ozone concentrations during the warm, sunny summer
months. This finding also suggests that ozone may
be an emerging issue in these rapidly growing areas.
- Eight-hour
average concentrations were also calculated. Standards
or objectives based on an 8-hour average are believed
to provide better protection against longer exposure
periods. There are currently no national objectives
based on an 8-hour averaging period. However, for
comparison purposes, 8-hour average concentrations
were evaluated against the U.K. standard of 50 ppb
(approximately 100 µg/m3). This level
was exceeded at most sites at least once per year,
and a maximum of 253 times in Kelowna in 1987.
For More Information:
Environmental Quality Branch
Ministry of Environment
Government of British Columbia
PO Box 9341, Stn Prov Govt
Victoria, British Columbia
Canada V8W 9M1
http://www.env.gov.bc.ca/air
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