2.1.2
The Common Pollutant Trends
The maximum 1-hour averages varied from about 60
between 1991-2000
ppb to over 540 ppb.  The highest hourly averages were
measured at the Windsor West site (College St.).  The
only exceedances of  the 1-hour objective of  250 ppb
Sulphur Dioxide (SO )
2
were observed at this site, with 12 exceedances in 1997.
Again in 1997, the same site experienced one exceedance
Over the last two decades, the ground level concentra-
of  the 24-hour objective (100 ppb).
tions of  sulphur dioxide in Windsor have for the most
part been well below the OMOE’s air quality objectives.
During the 1990-2001 period, mean annual concentra-
Nitrogen Dioxide (NO )
2
tions at the three SO  monitoring sites ranged from
2
about four ppb to over 12 ppb, all within the annual
The annual average NO  concentration at the downtown
2
Province’s AAQC of  20 ppb.  Data are provided for the
Windsor monitoring site has begun to show a slight
monitoring station in downtown Windsor.
decrease over the past few years, from 1997-2000 (Table
14).  This downward trend is consistent with the com-
concentrations were below the
Annual means of  SO
posite provincial trend during the 1990s.  It is attributed
2
Ministry of  the Environment’s Ambient Air Quality
to emission reductions from the industrial and transpor-
Criteria (AAQC)(Table 13) of  20 ppb;  the annual mean
tation sectors.
peaked between the years 1996-1997.  In 1997, 12
exceedances of  the 1-hour objective (250 ppb) were
The maximum 1-hour averages, except in 1993, were all
measured at the Windsor West site (College St).  That
within the provincial AAQC of  200 ppb.  That year, this
same year, the 24-hour objective (100 ppb) was exceeded
objective was exceeded during six hours.  The 24-hour
once.
objective (100 ppb) was also exceeded in 1993.  With the
exception of  the period 1993 to 1995, the trend in the
TABLE 13
Trend for Annual Mean SO (ppb)
annual maximum 1-hour averages was rather constant,
2
(Annual AAQC - 20 ppb)
with values near 100 ppb. .
Year
Station*
Windsor-Downtown
TABLE 14
Trend for NO Annual Mean (ppb)
2
No Annual Mean AAQC
1991
7.0
1992
6.0
1993
6.0
Year
Station
1994
6.0
Windsor-Downtown
1995
5.0
1996
10.0
1991
25.0
1997
6.7
1992
25.0
1998
7.4
1993
26.0
1999
6.7
1994
28.0
2000
6.2
1995
25.0
1996
26.0
* Data only available for Windsor-Downtown
1997
23.8
(OMOE-Air Quality Report-2000)
1998
23.8
1999
22.9
The lowest annual means were observed at the Windsor
2000
21.6
Downtown site (University Ave.)(Table 13), whereas the
(OMOE - Air Quality Report - 2000)
highest means were observed at the Windsor West site
(College St.); this trend continues from 1997 to present.
Peak annual means were observed in 1996 and 1997.
These trends are not supported by the emissions inven-
tory of  point sources in Windsor, suggesting that the
sources for these emissions are located outside of  the city.
22