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Ambient oxidant measurements at Toronto, Canada
TECHNICAL AMBIENT
OXIDANT (First
NOTE
MEASUREMENTS
received
16 Noaenlber
AT TORONTO,
1973 and in,jnalform
26 April
CANADA
1974)
Abstract-Ambient oxidant concentrations have been monitored at Toronto. Canada since 1970. During the first 2 years of the survey, more than 100 hourly concentrations in excess of IO pphm were observed. In the summer months, high oxidant concentration levels appeared to result from photochemical reactions since they were accompanied by the daily fluctuations of primary and secondary pollutants characteristic of photochemical activity. Simultaneous analysis of the oxidant monitoring data and continuous records of meteorological parameters showed that high oxidant concentrations occurred on days of high temperatures, long solar irradiation periods and sourtherly winds. The analysis indicated that the oxidant precursors may have originated from sources to the south of Toronto.
INTRODUCTION
Photochemically-produced oxidant, originally identified in Los Angeles. has since been observed in other U.S. cities (Wanta et al., 1961; Leone et al., 1968; Tebbens, 1968). More recently, areas previously considered unlikely locations for photochemical activity because of their low levels of solar irradiation and primary pollutant concentrations, have been found to exhibit similar if weaker signs. Wisse and Velds (1970) reported oxidant concentrations in excess of 10 pphm at Vlaardingen, The Netherlands, during summer and autumn days. Similarly high oxidant concentrations have been measured at Frankfurt/Main (Jost, 1970), at Aspendale, Victoria (Galbally, 1970) and in southern England (Atkins rt al., 1972). In the Toronto metropolitan area, ambient oxidant concentrations have been monitored since 1970 as part of the Ontario Government’s Air Management Branch monitoring program. Results of the 1970 and 1971 surveys have been made available and are analysed here to determine the extent of the photochemical activity and the influence of several meteorological parameters. LOCATION
AND
SOURCE
OF
DATA
The metropolitan Toronto area, located on the north shore of Lake Ontario, has a total population of about 2.5 million. The lake is large and deep and hence has a strong influence on the mesoscale climatology of the area. Lake breezes occur during spring and summer (Hirt and Shaw, 1973). The flow of warm air from land towards the cold lake leads to stable layering during the day, as pointed out by Brewer (1968). Oxidant measurements by the potassium iodide method are made at three locations in Toronto. The method is sensitive to oxone but other oxidants such as nitrogen dioxide, aldehydes and peroxyacyl nitrates have a positive interference. The strong negative interference of sulphur dioxide is reduced by utilizing a chromium trioxide scrubber (see Katz, 1968 for a review of the method). Hydrocarbons are measured as total hydrocarbons, methane equivalent, using a Beckman 400 continuous flame ionization detector, and nitrogen oxides are measured by the Saltzman method using a Beckman Acralyzer (Katz, 1968). Wind speed and direction at the 10 m level are monitored at several locations in Toronto. Data from two such stations were used as appropriate for each oxidant monitoring station. Hours of sunshine and daily mean temperatures were available from a mid-town station. Locations are shown in Fig. 1. RESULTS
Euidrncv
of photochrmical
oxidant
AND
DISCUSSION
formation
Table I presents a summary of the number of hours the measured oxidant concentrations have exceeded the Provincial standard of 10pphm. The variability from station to station and from year to year is obvious and is m part due to instrument downtime. For instance, in July 1971, station 34002 reported no casts of oxidant concentrations in excess of 1Opphm while station 35003 reported 35 such cases. The amount of data available for that month, however, was only 13 per cent for the first station compared with 80 per cent for the second. Ground level concentrations in excess of 10 pphm are generally considered evidence of photochemical activity (U.S. Department of Education, Health and Welfare, 1970). Figure 2 shows the daily concentration history of primary (nitrogen oxides and hydrocarbons) and secondary (oxidant) photochemical pollutants averaged for the month of August, 1970 at station 34002. The pattern resembles those observed in Los Angeles and other U.S. cities (Tebbens, 1968; Lynn and McMullen, 1966) and is characterized by a nitrogen oxides peak during the ,\I XI,
I
1195
Technical
.3
Fig. 1. Details of the Toronto
area showing
note
Lake
Ontorto
the location of sampling call stations, A.
stations.
0. and metcorologi-
morning rush hour and an oxidant peak in the afternoon. During the early winter (November 1970) the oxidant peak is much less pronounced as shown in Fig. 3. The frequency of occurrence of high oxidant concentrations in the Toronto area and the daily pattern of concentrations of primary and secondary pollutants is interpreted as evidence of photochemical activity.
t F’FFCTOF MtTI’OKOl_OGlt%I. w&d
\ \KlhBI.I‘S
.spwd urrd ~j~~~~r;~~7
Pollutant wind roses (Munn, 1969) were constructed by averaging all pollutant coil~eiltr~~ti~~l~sassocratcd with winds from each of the eight sectors and speed sub-classes 0, l- 5. (F IO. etc. Seasonal and diurnal cycles were reduced (but certainly not eliminated) by including observations made during the months of April September
Table
I. Hourly
oxidant data in Toronto ._____ ____I__~__~~__
(a) Nulnber of cases in chills the IOpphl~~ ~~o~ir~~oxid‘mt ~~~~~~~~ltr~~t~~~~~ was exceeded in 1970 and 1971 at the Toronto sampling stations Number of cases I’)71 I970 Station
--l_______-._-..----. 0 itr i 30 .- l-ll. --- ---~-
C) IO0 Y -___~-
31001 34002 35003 (h) Percentage
Month April May June July August September
ofoxidant data 34002 84 82 51 X8 71 55
valid for the Toronto sampling Percentage of data valtd lY71 1970 35003 iJot! 20 I4 0 0 71 Y
IX 45 73 13 4x 0 __
__._
- 1...-. -stations
3 5003 43 20 36 80 XI: 60
Technical note
Tome
1197
of day
Fig. 2. Hourly average pollutant concentrations at station 34002. August 1970. and from 07:OO to 19:00 h, local standard time, in both 1970 and 1971. Wind data from the two airports (Fig. 1)were compared and found to correlate well with each other. Nevertheless, for the construction of the pollutant wind roses, it was decided to use the data from the measuring station nearest the oxidant sampling station in question. Figure 4 shows the oxidant wind rose for station 34002 with winds measured at the Toronto Island Airport. Figure 5 shows similar results for station 35003 and winds measured at the Toronto International Airport. The wind roses for the two oxidant monitoring stations are similar and show some interesting features. The highest oxidant concentrations are associated with winds from the south sector (S.EPSS.W) while the lowest oxidant concentrations are associated with winds from the north. These results agree with work by Munn (1973) who found that particulate concentrations at two Toronto locations were well correlated and that the highest concentrations occurred during days of S-S.S.W winds while N--N.N.E winds led to the best air quality. Lake breeze winds led to intermediate concentrations. Likewise a study by Mukammal (1964) into the damage to tobacco on the north shores of Lake Erie revealed that the worst damage was associated with large scale air masses which had travelled over polluted areas in the south. Wind speed, lake breezes,
temperature
and solar irradiation
Although the oxidant wind rose analysis of the previous section identified the importance of wind direction, it failed to di~erentiate between large scale southerly air mass movements and localized lake-breeze circulations
‘UP 04.00
C8CO
12cO
16:CO 20.00
Fig. 3. Hourly average pollutant concentrations at station 34002, November 1970.
Technical
note
N
NE
NY! _~2 4’ ‘/ ,3;
,,.
-2
4
s OX
Fig. 4. Oxidant
whm
wmd rose for observations at station 34002 and Toronto (Wind speed. miles h- ‘.)
and led to the apparent contradiction that better ventilation (higher wind dant concentrations. These questions, as well as the effect of temperature dered. The wind data from the two airport stations and the temperature and Street station were used to separate all days into three classes. The north which the winds were from the N&N-N.W W sectors. the south winds
Island Airport
speeds) is associated and solar irradiation
wind data
with higher oxiare now consi-
solar irradiation data from the Bloor winds class included all days during class all days during which the winds
w-
S
Fig. 5. Oxidant
OX
whm
wind rose for observations at statlon 35003 and Toronto wind data. (Wind speed. miles h- I.)
International
Airpol-t
1199
Technical note Table 2. Effect of mean temperature and hours of bright sunshine on the mean oxidant concentration three classes of wind direction (station 34002) t* $ 2 Number of cases Oxidant North winds Tt < 50 T > 50 South winds Tc 50 T 2 50 Lake breeze T> 50 * t Hours of sunshine. * T Mean daily temperature,
i
for the
(28 Number of cases Oxidant
31 22
2.7 2.1
23 19
3.2 3.5
22 31
3.8 4.3
15 13
2.3 3.2
17 13
3.5 4.4
6 37
5.0 6.7
3
2.2
9
* 3.7
42
4.3
F.
blew from the E-SE-S-SW sectors and the lake-breeze class days with high temperature, large number of sunshine hours, light winds and a shift in wind direction from calm or offshore in the morning to onshore in the afternoon. In connection with this classification, daily mean oxidant concentrations were calculated for all days with valid data at stations 34002 and 35003. To do this, the hour at which the oxidant peak occurred was observed and then a 9 h average centered about the peak hour was evaluated. This 9 h period corresponded roughly to the length of time between morning buildup and late afternoon fall of oxidant concentration. Tables 2 and 3 show the effect of temperature and hours of solar irradiation on the mean oxidant concentrations for the three wind direction classes. Again the highest oxidant concentrations are associated with south winds. while north winds lead to the lowest oxidant concentrations. Lake breeze days, during which primary pollutants are emitted in Toronto, transported over the lake and back to Toronto in the afternoon, lead to intermediate concentrations. Oxidant concentrations at Toronto show a strong dependence on temperature and hours of solar irradiation. For each wind direction subclass an increase in the number of hours of sunshine leads to an increase in the daily mean oxidant condensation. Qualitatively this agrees with the results of laboratory irradiation of Los Angeles atmosphere samples (Kopczynski et al., 1972). High temperatures are associated with high oxidant concentrations in the case of south and north winds. It is not possible to infer whether this is a direct influence as suggested by Leighton (1961) or an indirect effect through some other meteorological parameter. Schuck et al. (1966) in Los Angeles and Leone et al. (1968) in New Jersey found that oxidant concentration was inversely related to wind speed. The apparent contradiction observed here in the oxidant wind roses was investigated by calculating the average oxidant and wind speed as a function of time of day for each of the three wind direction classes. The results for station 34002 are shown in Fig. 6. It is obvious that the two quantities Table 3. Effect of mean temperature and hours of bright sunshine on the mean oxidant concentration three classes of wind direction (station 35003)
t* < 2 Number of cases Oxidant North winds Tt< 50 T> 50 South winds T i 50 T2 50 Lake breeze T > 50 * r Hours of bright sunshine. ‘l T Mean daily temperature.
F.
3
for the
f>8 Number of cases Oxidant
20 19
1.9 2.6
14 11
2.9 4.0
8 22
2.9 4.5
33 17
2.2 3.9
17 19
2.3 4.7
11 35
2.5 6.7
3
2.9
6
4.9
39
6.1
12(H)
Technical
13
, - ,South
12
-_ >
/
IO
1
winds
\
\,’
11
note
:
North winds’
9 8 71 6 5 4 ;
a
0”““”
04 00 0800
I ’ ”
I ”
12 00
”
”
”
0”““““““““““”
”
16 00 20-00
Time of day
b
04-00
08.00
1200
16:co
2000
Time of day
Fig. h. Daily pattern of wind speed and oxidant concentration for days of more than 8 h of bright sunshine. Oxidants measured at station 34002 and wind speed at Toronto Island Airport.
art‘ highlq correlated. each reaching a peak in mid-afternoon, concentration increasing with wind speed.
and that. therefore,
the wind roses will show oxidant
There is evidence of photochemical oxidant formation in the Toronto area as shown by the number of hours the concentration has exceeded the IO pphm level and by the plots of the daily patterns of primary and secondary pollutants involved in these reactions. The highest oxidant concentrations occur with southerly winds (from the sector SE-SW). This suggests that the primary pollutants leading to oxidant formation are emitted either in communities to the south of Toronto or in Toronto itself followed by transport to and from the lake with reaction in between. A differentiation between these two possibilities was attempted with the result that, since days of lake breeze are associated with intermediate oxidant concentrations. emissions of primary pollutants in communities to the south of Toronto appear to explain part of the oxidant pollution measured in Toronto. Temperature and duration of bright sunshine are other important meteorological parameters. For a subdivlGon of all days into three wind direction classes an increase in these variables results in an increase in the observed daily oxidant concentration l~.h,lo,l,ktlyc,ft~~~~r.\ Financial support through a National Research Council of Canada scholarship to 0. Melo and from the Atkinson Charitable Foundation and the Dept. of the Environment, Ontario is acknowledged with gratitude. Dr. M. Lusis and Mr. Y. Nguyen contributed immensely by means of discussion to the work presented here. The cooperation of the Ontario Air Management Branch and Mr. D. Ogner especially is appreciated. The meteorological data were supplied by the Atmospheric Environment Service. Environment Canada. 0 CAV,O I-. Mt~o C‘OLIS R. PHILLIPS
Atkins D. H F.. Cox R. A. and Eggleton A. E. J. (1972) PhotochemIcal ozone and sulphuric acid aerosol formation in the atmosphere over southern England. Naf~rc 235, 372-376. Brcwcr 4. W. (lY6X) Discussion: The manne layer and its relation to il smog epsldc III Riverside. California 4 t/tro,s$f~~ric Efrc~im~m~r 2. 623. Galbally I. E. ( 1971 ) Surface o/one observations at Aspendale, Victoria. 1964 1970. .4 twosphrricEm~womm~~~/ 5. 15 75. Hit-t M. S. and Shaw R. W. ( 1973) Passage of a lake breeze through ToI-onto. Atn~osphr~rrc C‘nr~r~~!n(~!~t7. 63 73.
Technical
note
1201
Jost D. (1970) Survey of the distribution of trace substances in pure and polluted atmospheres. J. Purr Appl. Chrm. S&643-654. Katz M. (1968) Analysis of inorganic gaseous pollutants. In Air Pollution (Edited by Stern A. C.). Vol. 2. 2nd Edn., 684 pp. Academic Press, New York. Kopczynski S. L., Lonneman W. A., Sutterfield F. D. and Darley P. E. (1972) Photochemistry of atmospheric samples in Los Angeles. Environ. Sci. Technol. 6, 3422347. Leighton P. A. (1961) Photochemistry of Air Pollution, 300 pp. Academic Press, New York. Leone J. A., Brennan E. and Daines R. H. (1968) The relationship of wind parameters in determining oxidant concentrations in two New Jersey Communities. Atmospheric Environment 2, 25533. Lynn D. A. and McMullen T. B. (1966) Air pollution in six major U.S. cities as measured by the continuous air monitoring program. J. Air. Pollur. Conrrol Ass. 16, 186190. Mukammal E. I. (1964) Ozone as a cause of tobacco injury. Agr. Mrteorol. 2, 145165. Munn R. E. (1973) A study of suspended particulate air pollution at two locations in Toronto. Canada. Atmospheric Enuironmrnt 7, 31 l-318. Munn R. E. (1969) Pollution wind-rose analysis. Atmosphere 7, 97-105. Schuck E. A., Pitts J. N., Jr. and Wan J. K. S. (1966) Relationships between certain meteorological factors and photochemical smog. Int. J. Air Wut. Pollut. IO, 689-71 I. Tebbens B. D. (1968) Gaseous pollutants in the air. In Air Pollution (Edited by Stern A. C.), Vol. I, 2nd Edn.. 6Y4 pp. Academic Press, New York. U.S. Department of Education, Health and Welfare, Washington (1970) Air Quality Criteria for Photochemical Oxidants, Chap. 3. Wanta R. C., Moreland W. B. and Heggestad H. E. (1961) Trophospheric ozone, an air pollution problem arising in the Washington, D.C. metropolitan area. Mon. Weather Rru. 89, 289-296. Wisse J. A. and Velds C. A. (I 970) Preliminary discussion on ozone oxidant measurements at Vlaardingen, The Netherlands. Atmospheric Environment 4, 79-85.
OXIDANT (First
NOTE
MEASUREMENTS
received
16 Noaenlber
AT TORONTO,
1973 and in,jnalform
26 April
CANADA
1974)
Abstract-Ambient oxidant concentrations have been monitored at Toronto. Canada since 1970. During the first 2 years of the survey, more than 100 hourly concentrations in excess of IO pphm were observed. In the summer months, high oxidant concentration levels appeared to result from photochemical reactions since they were accompanied by the daily fluctuations of primary and secondary pollutants characteristic of photochemical activity. Simultaneous analysis of the oxidant monitoring data and continuous records of meteorological parameters showed that high oxidant concentrations occurred on days of high temperatures, long solar irradiation periods and sourtherly winds. The analysis indicated that the oxidant precursors may have originated from sources to the south of Toronto.
INTRODUCTION
Photochemically-produced oxidant, originally identified in Los Angeles. has since been observed in other U.S. cities (Wanta et al., 1961; Leone et al., 1968; Tebbens, 1968). More recently, areas previously considered unlikely locations for photochemical activity because of their low levels of solar irradiation and primary pollutant concentrations, have been found to exhibit similar if weaker signs. Wisse and Velds (1970) reported oxidant concentrations in excess of 10 pphm at Vlaardingen, The Netherlands, during summer and autumn days. Similarly high oxidant concentrations have been measured at Frankfurt/Main (Jost, 1970), at Aspendale, Victoria (Galbally, 1970) and in southern England (Atkins rt al., 1972). In the Toronto metropolitan area, ambient oxidant concentrations have been monitored since 1970 as part of the Ontario Government’s Air Management Branch monitoring program. Results of the 1970 and 1971 surveys have been made available and are analysed here to determine the extent of the photochemical activity and the influence of several meteorological parameters. LOCATION
AND
SOURCE
OF
DATA
The metropolitan Toronto area, located on the north shore of Lake Ontario, has a total population of about 2.5 million. The lake is large and deep and hence has a strong influence on the mesoscale climatology of the area. Lake breezes occur during spring and summer (Hirt and Shaw, 1973). The flow of warm air from land towards the cold lake leads to stable layering during the day, as pointed out by Brewer (1968). Oxidant measurements by the potassium iodide method are made at three locations in Toronto. The method is sensitive to oxone but other oxidants such as nitrogen dioxide, aldehydes and peroxyacyl nitrates have a positive interference. The strong negative interference of sulphur dioxide is reduced by utilizing a chromium trioxide scrubber (see Katz, 1968 for a review of the method). Hydrocarbons are measured as total hydrocarbons, methane equivalent, using a Beckman 400 continuous flame ionization detector, and nitrogen oxides are measured by the Saltzman method using a Beckman Acralyzer (Katz, 1968). Wind speed and direction at the 10 m level are monitored at several locations in Toronto. Data from two such stations were used as appropriate for each oxidant monitoring station. Hours of sunshine and daily mean temperatures were available from a mid-town station. Locations are shown in Fig. 1. RESULTS
Euidrncv
of photochrmical
oxidant
AND
DISCUSSION
formation
Table I presents a summary of the number of hours the measured oxidant concentrations have exceeded the Provincial standard of 10pphm. The variability from station to station and from year to year is obvious and is m part due to instrument downtime. For instance, in July 1971, station 34002 reported no casts of oxidant concentrations in excess of 1Opphm while station 35003 reported 35 such cases. The amount of data available for that month, however, was only 13 per cent for the first station compared with 80 per cent for the second. Ground level concentrations in excess of 10 pphm are generally considered evidence of photochemical activity (U.S. Department of Education, Health and Welfare, 1970). Figure 2 shows the daily concentration history of primary (nitrogen oxides and hydrocarbons) and secondary (oxidant) photochemical pollutants averaged for the month of August, 1970 at station 34002. The pattern resembles those observed in Los Angeles and other U.S. cities (Tebbens, 1968; Lynn and McMullen, 1966) and is characterized by a nitrogen oxides peak during the ,\I XI,
I
1195
Technical
.3
Fig. 1. Details of the Toronto
area showing
note
Lake
Ontorto
the location of sampling call stations, A.
stations.
0. and metcorologi-
morning rush hour and an oxidant peak in the afternoon. During the early winter (November 1970) the oxidant peak is much less pronounced as shown in Fig. 3. The frequency of occurrence of high oxidant concentrations in the Toronto area and the daily pattern of concentrations of primary and secondary pollutants is interpreted as evidence of photochemical activity.
t F’FFCTOF MtTI’OKOl_OGlt%I. w&d
\ \KlhBI.I‘S
.spwd urrd ~j~~~~r;~~7
Pollutant wind roses (Munn, 1969) were constructed by averaging all pollutant coil~eiltr~~ti~~l~sassocratcd with winds from each of the eight sectors and speed sub-classes 0, l- 5. (F IO. etc. Seasonal and diurnal cycles were reduced (but certainly not eliminated) by including observations made during the months of April September
Table
I. Hourly
oxidant data in Toronto ._____ ____I__~__~~__
(a) Nulnber of cases in chills the IOpphl~~ ~~o~ir~~oxid‘mt ~~~~~~~~ltr~~t~~~~~ was exceeded in 1970 and 1971 at the Toronto sampling stations Number of cases I’)71 I970 Station
--l_______-._-..----. 0 itr i 30 .- l-ll. --- ---~-
C) IO0 Y -___~-
31001 34002 35003 (h) Percentage
Month April May June July August September
ofoxidant data 34002 84 82 51 X8 71 55
valid for the Toronto sampling Percentage of data valtd lY71 1970 35003 iJot! 20 I4 0 0 71 Y
IX 45 73 13 4x 0 __
__._
- 1...-. -stations
3 5003 43 20 36 80 XI: 60
Technical note
Tome
1197
of day
Fig. 2. Hourly average pollutant concentrations at station 34002. August 1970. and from 07:OO to 19:00 h, local standard time, in both 1970 and 1971. Wind data from the two airports (Fig. 1)were compared and found to correlate well with each other. Nevertheless, for the construction of the pollutant wind roses, it was decided to use the data from the measuring station nearest the oxidant sampling station in question. Figure 4 shows the oxidant wind rose for station 34002 with winds measured at the Toronto Island Airport. Figure 5 shows similar results for station 35003 and winds measured at the Toronto International Airport. The wind roses for the two oxidant monitoring stations are similar and show some interesting features. The highest oxidant concentrations are associated with winds from the south sector (S.EPSS.W) while the lowest oxidant concentrations are associated with winds from the north. These results agree with work by Munn (1973) who found that particulate concentrations at two Toronto locations were well correlated and that the highest concentrations occurred during days of S-S.S.W winds while N--N.N.E winds led to the best air quality. Lake breeze winds led to intermediate concentrations. Likewise a study by Mukammal (1964) into the damage to tobacco on the north shores of Lake Erie revealed that the worst damage was associated with large scale air masses which had travelled over polluted areas in the south. Wind speed, lake breezes,
temperature
and solar irradiation
Although the oxidant wind rose analysis of the previous section identified the importance of wind direction, it failed to di~erentiate between large scale southerly air mass movements and localized lake-breeze circulations
‘UP 04.00
C8CO
12cO
16:CO 20.00
Fig. 3. Hourly average pollutant concentrations at station 34002, November 1970.
Technical
note
N
NE
NY! _~2 4’ ‘/ ,3;
,,.
-2
4
s OX
Fig. 4. Oxidant
whm
wmd rose for observations at station 34002 and Toronto (Wind speed. miles h- ‘.)
and led to the apparent contradiction that better ventilation (higher wind dant concentrations. These questions, as well as the effect of temperature dered. The wind data from the two airport stations and the temperature and Street station were used to separate all days into three classes. The north which the winds were from the N&N-N.W W sectors. the south winds
Island Airport
speeds) is associated and solar irradiation
wind data
with higher oxiare now consi-
solar irradiation data from the Bloor winds class included all days during class all days during which the winds
w-
S
Fig. 5. Oxidant
OX
whm
wind rose for observations at statlon 35003 and Toronto wind data. (Wind speed. miles h- I.)
International
Airpol-t
1199
Technical note Table 2. Effect of mean temperature and hours of bright sunshine on the mean oxidant concentration three classes of wind direction (station 34002) t* $ 2 Number of cases Oxidant North winds Tt < 50 T > 50 South winds Tc 50 T 2 50 Lake breeze T> 50 * t Hours of sunshine. * T Mean daily temperature,
i
for the
(28 Number of cases Oxidant
31 22
2.7 2.1
23 19
3.2 3.5
22 31
3.8 4.3
15 13
2.3 3.2
17 13
3.5 4.4
6 37
5.0 6.7
3
2.2
9
* 3.7
42
4.3
F.
blew from the E-SE-S-SW sectors and the lake-breeze class days with high temperature, large number of sunshine hours, light winds and a shift in wind direction from calm or offshore in the morning to onshore in the afternoon. In connection with this classification, daily mean oxidant concentrations were calculated for all days with valid data at stations 34002 and 35003. To do this, the hour at which the oxidant peak occurred was observed and then a 9 h average centered about the peak hour was evaluated. This 9 h period corresponded roughly to the length of time between morning buildup and late afternoon fall of oxidant concentration. Tables 2 and 3 show the effect of temperature and hours of solar irradiation on the mean oxidant concentrations for the three wind direction classes. Again the highest oxidant concentrations are associated with south winds. while north winds lead to the lowest oxidant concentrations. Lake breeze days, during which primary pollutants are emitted in Toronto, transported over the lake and back to Toronto in the afternoon, lead to intermediate concentrations. Oxidant concentrations at Toronto show a strong dependence on temperature and hours of solar irradiation. For each wind direction subclass an increase in the number of hours of sunshine leads to an increase in the daily mean oxidant condensation. Qualitatively this agrees with the results of laboratory irradiation of Los Angeles atmosphere samples (Kopczynski et al., 1972). High temperatures are associated with high oxidant concentrations in the case of south and north winds. It is not possible to infer whether this is a direct influence as suggested by Leighton (1961) or an indirect effect through some other meteorological parameter. Schuck et al. (1966) in Los Angeles and Leone et al. (1968) in New Jersey found that oxidant concentration was inversely related to wind speed. The apparent contradiction observed here in the oxidant wind roses was investigated by calculating the average oxidant and wind speed as a function of time of day for each of the three wind direction classes. The results for station 34002 are shown in Fig. 6. It is obvious that the two quantities Table 3. Effect of mean temperature and hours of bright sunshine on the mean oxidant concentration three classes of wind direction (station 35003)
t* < 2 Number of cases Oxidant North winds Tt< 50 T> 50 South winds T i 50 T2 50 Lake breeze T > 50 * r Hours of bright sunshine. ‘l T Mean daily temperature.
F.
3
for the
f>8 Number of cases Oxidant
20 19
1.9 2.6
14 11
2.9 4.0
8 22
2.9 4.5
33 17
2.2 3.9
17 19
2.3 4.7
11 35
2.5 6.7
3
2.9
6
4.9
39
6.1
12(H)
Technical
13
, - ,South
12
-_ >
/
IO
1
winds
\
\,’
11
note
:
North winds’
9 8 71 6 5 4 ;
a
0”““”
04 00 0800
I ’ ”
I ”
12 00
”
”
”
0”““““““““““”
”
16 00 20-00
Time of day
b
04-00
08.00
1200
16:co
2000
Time of day
Fig. h. Daily pattern of wind speed and oxidant concentration for days of more than 8 h of bright sunshine. Oxidants measured at station 34002 and wind speed at Toronto Island Airport.
art‘ highlq correlated. each reaching a peak in mid-afternoon, concentration increasing with wind speed.
and that. therefore,
the wind roses will show oxidant
There is evidence of photochemical oxidant formation in the Toronto area as shown by the number of hours the concentration has exceeded the IO pphm level and by the plots of the daily patterns of primary and secondary pollutants involved in these reactions. The highest oxidant concentrations occur with southerly winds (from the sector SE-SW). This suggests that the primary pollutants leading to oxidant formation are emitted either in communities to the south of Toronto or in Toronto itself followed by transport to and from the lake with reaction in between. A differentiation between these two possibilities was attempted with the result that, since days of lake breeze are associated with intermediate oxidant concentrations. emissions of primary pollutants in communities to the south of Toronto appear to explain part of the oxidant pollution measured in Toronto. Temperature and duration of bright sunshine are other important meteorological parameters. For a subdivlGon of all days into three wind direction classes an increase in these variables results in an increase in the observed daily oxidant concentration l~.h,lo,l,ktlyc,ft~~~~r.\ Financial support through a National Research Council of Canada scholarship to 0. Melo and from the Atkinson Charitable Foundation and the Dept. of the Environment, Ontario is acknowledged with gratitude. Dr. M. Lusis and Mr. Y. Nguyen contributed immensely by means of discussion to the work presented here. The cooperation of the Ontario Air Management Branch and Mr. D. Ogner especially is appreciated. The meteorological data were supplied by the Atmospheric Environment Service. Environment Canada. 0 CAV,O I-. Mt~o C‘OLIS R. PHILLIPS
Atkins D. H F.. Cox R. A. and Eggleton A. E. J. (1972) PhotochemIcal ozone and sulphuric acid aerosol formation in the atmosphere over southern England. Naf~rc 235, 372-376. Brcwcr 4. W. (lY6X) Discussion: The manne layer and its relation to il smog epsldc III Riverside. California 4 t/tro,s$f~~ric Efrc~im~m~r 2. 623. Galbally I. E. ( 1971 ) Surface o/one observations at Aspendale, Victoria. 1964 1970. .4 twosphrricEm~womm~~~/ 5. 15 75. Hit-t M. S. and Shaw R. W. ( 1973) Passage of a lake breeze through ToI-onto. Atn~osphr~rrc C‘nr~r~~!n(~!~t7. 63 73.
Technical
note
1201
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