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Ambient Air Measurements of Benzene in Canada (1989-1998)
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Executive Summary
The Analysis and Air Quality Division of the
Environmental Protection Service, Environment Canada (EC) has operated a field measurement
program for benzene and other volatile organic compounds (VOCs) in ambient air since 1989.
With the cooperation of provincial and municipal environmental agencies, samples have been
collected at over 50 urban and rural monitoring sites across the country. The collected
data from the monitoring program are used to assess population exposure to benzene and
other air toxics as well as to support photochemical oxidant assessment and control
activities. Previous reports and publications on the results of the program have been
prepared and distributed. This paper provides an update on these earlier works and was
prepared additionally as a supporting document for the proposed Canada Wide Standard (CWS)
for benzene. Results from an Ontario Ministry of Environment (OME) benzene monitoring
program (17 additional unique sites) are also included in the data analysis. Sites are
compared based on location (rural, suburban and urban) and in terms of source influences
(transportation and industrial). Seasonal and day of week variations in benzene
concentrations are examined and trends in benzene levels over the period are analyzed for
sites with complete data.
Samples are normally collected over 24-h sampling periods once every six days. At many
sites, more intensive VOC sampling campaigns have been carried out (to support the ground
level ozone science program) with samples collected over three, four or twelve hour
sampling periods. Ambient air samples are collected in stainless steel canisters and
analyzed using a cryogenic pre-concentration technique with a high-resolution gas
chromatograph and quadropole mass-selective detector (GC-MSD).
An extensive database of ambient air benzene observations is available for Canada for
the 1989 to 1998 time period. Mean benzene concentrations (using data for all years)
ranged from 10.3 µg/m³ at an urban site influenced by emissions from a coke oven/iron
and steel mill facility (Sault Ste. Marie-Bonney St.) to 0.3 µg/m³ at a rural remote
site (Kejimkujik National Park in Nova Scotia). For typical (i.e. not adjacent to
roadways) urban site locations with no industrial source influences, mean benzene
concentrations over the period were in the range of 1.8 to 3.6 µg/m³. Mean and median
benzene concentrations are highest at urban-street sites and at sites influenced by
industrial sources and lowest at rural and suburban sites.
For the most recent years of measurements (1995 to 1997), mean concentrations at the
urban/suburban sites ranged from 1.0 to 3.5 µg/m³ with most sites (31 out of 40)
recording mean concentrations of less than 2.5 µg/m³. Ninetieth percentile
concentrations at these sites ranged from 1.5 to 6.6 µg/m³ with most sites (31 out of
40) recording 90th percentile concentrations of less than 4.5 µg/m³. For the
rural sites mean concentrations ranged between 0.3 and 0.8 µg/m³ with 90th
percentile concentrations ranging between 0.6 and 1.7 µg/m³. For sites near roadways or
near industrial sources, mean benzene concentrations ranged from 4.1 to 13.1 µg/m³ and
90th percentile concentrations varied from 8.0 to 36.0 µg/m³.
Most sites recorded decreases in benzene concentrations between 1990 and 1997. Using
the composite results for urban sites with complete data there was a 25% reduction in
annual mean benzene concentrations between 1990 and 1995 followed by a small increase
between 1996 and 1997. Results for individual sites are quite variable with percentage
reductions between 1990 and 1996 ranging from 0 to 50 %. A number of sites with the
highest mean concentrations showed little or no improvement over the period.
A complete emission inventory trend analysis has not yet been completed, but the
decline in ambient benzene levels at most urban sites is a result of improved VOC emission
control technology on new motor vehicles plus the effect of reduced gasoline benzene
levels. The relationship between emissions and ambient levels of benzene will be explored
in a later report. The lack of improvement in benzene levels at some sites with high
concentrations will also be investigated.
For full transcript please contact:
e-mail: Tom Dann
phone: (613) 991-9459.
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