EcoSysP Filling Station Monitoring for Benzene

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EcoSys-P Filling Station Monitoring for
Benzene     Overview   An EcoSys-P portable mass
spectrometer was used to monitor Benzene levels
close to the pumps of a Gas station adjacent to a
city road. The service station had two islands,
each containing two multi-fuels pumps. Each of
the six pumps was able to dispense 95 Octane
unleaded, 98 octane unleaded and Diesel.   The
station had a canopy at 2.6M above the forecourt
and a small shop and payment window some 4.4M
away from the nearest pump and 9.6M from the
distant pump.   The instrument was set up on the
forecourt adjacent to the payment window with the
probe sampling close to the payment window at
approximately mouth height (1.65M). The
experiment was run over a period of three days.
Wind speed and direction was recorded along with
the concentration data using external devices
attached to the analogue inputs of the ecoSys-P
analyser.  
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Method   The instrument was brought to site,
switched on for a period of three hours. The
system was calibrated with a 100ppb Benzene,
standard gas and a grade 6.0 zero Nitrogen
standard. Gas samples were introduced using a
membrane inlet with a small circulating pump on
the vent side of the inlet line. A gas flow of
50mL/Min was established and used throughout the
test. Zero and Span gases were connected directly
to the sample line at the mouth height sample
point adjacent to the forecourt payment window.
    The instrument was configured to run a zero
gas acquisition under the Nitrogen 6.0 standard
using the file benzero. The system was
calibrated under the 100ppb Benzene, standard
using the file bencal1 and then set to run a
simple five-channel measurement of benzene in air
using the measurement file benrun1. The
measurements were configured to run with a dwell
time of 5 seconds per mass giving a cumulative
update time of 25 seconds. To avoid creating
large data files, the instrument was set to run
the measurements in timer mode every 2 minutes.
See files attached in appendix 1.   After
calibration, the instrument was set to run for
three days starting at 0001 on a Monday and
ending at 1159 the following Wednesday.
Continuous measurements were logged along with a
manual calibration check every 6 hours. The
results are shown after processing in Microsoft
Excel in Appendix 1A.
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Results Summary and Conclusions   Day 1 Wind
conditions were very light with no recorded
speeds for most of this monitoring period.
Accordingly, dispersion around the forecourt area
was unlikely as a result of wind speed or
direction. Average wind speed was just 3.3mph and
no predominant direction could be recorded. Data
shows clear peaks around the morning, lunchtime
and evening peak hours with values returning
close to ambient in the quiet hours 0000
through 0400     Day 2 Monitoring shows reduced
maxima but still has clear trends during peak
hours. Wind speed was higher with an average of
7.6 mph and a predominant direction from the
North, which was likely to cause some dispersion
around the forecourt.     Day 3 Wind speeds
were considerably higher with average of 17.5mph.
The increased wind speed would certainly produce
a dispersion effect around the forecourt but more
significantly, the predominant wind was from the
East. This would have the effect of blowing
benzene southwards away from the sample point at
the payment window. The result was very
significantly reduced exposure levels at the
payment window. Whilst this was obviously
beneficial for customers at the window and the
cashiers, the total amount of benzene released
would have been similar to the average for the
previous days. This would have been dispersed
downwind effecting properties to the West of the
service station.
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• Summary
•  
• EcoSys-P was able to provide valuable real-time
  information on exposure to Benzene. The addition
  of wind speed and direction as analogue inputs
  allows powerful modelling of trends in terms of
•  
• Concentration V time
• Concentration V Wind Speed
• Concentration V Wind Direction
•  
• EcoSys-P was able to accurately trend data over
  long periods with regular calibration checks
  showing little drift. Data collected could be
  modelled to give important safety guidance for
  employee, customer

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Layout of Gas station site
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Example of MID zero gas file for Benzene at mass
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Conditions Average Wind Speed
3.3MPH Predominant wind direction NA
 
Results for Monday 14/07/04
  Results follow trends in rush hour traffic
patterns. Concentrations are not diluted by wind
due to overall still conditions on the test
day.          

 
 
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Results for Wednesday 16/07/04  
Conditions
Average Wind speed 17.5MPH Predominant Wind
Direction E   Although there is still
correlation between rush hour traffic patterns
and results at the payment window, the increased
winds and particularly the dilution effect of the
Easterly wind blowing benzene in the opposite
direction has significantly reduced exposure at
the window.
 
 
 
 
 
 
 
 
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Results for Three Days
Wind dilution has some effect on concentrations
at the payment window, which is related to speed.
Wind direction has a much more significant
effect on concentrations at the payment window
with reductions towards background seen when the
wind was coming from the East and acting directly
to reduce concentrations at the window (up-wind).
Whilst this significantly reduces exposure at the
window it does, of course, move the exposure
downwind to the West.
 
 

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Further supporting data                          
 
Real Time measurements of BTX from a 1.2L petrol
vehicle exhaust at idle.
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  Real time data from a Tedlar sample bag used
for BTX from the vehicle exhaust. High BTX levels
can still be seen after washing out the bag with
five full 100 Nitrogen refills.
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  Spectrum taken under vehicle exhaust gas
showing BTX mass groups.