Characteristics of the Interactions Pattern of Surface Ozone
with its Precursors in the Fraser Valley, British Columbia
Paper Number: 441
Mizanur Rahman1,3, Berry, Joffre2, Nagaya, Yuichi1, Hashimoto, Atsushi.1, Kameoka,
Takaharu1
1
Dept. of Sustainable Resource Sciences, Mie University, 1515 Kamihama, Tsu, Mie, Japan
BC Institute of Technology, 3700 Burnaby, BC, V5G 3H2, Canada
3
Correspondence:+8159 231 9548, mizan@bife.bio.mie-u.ac.jp, mizan_rahman60@hotmail.com
2
ABSTRACT
Hourly raw ambient data on air criteria pollutants of Greater Vancouver Regional District
(GVRD), British Columbia were analyzed to investigate the relationships of ozone with its
precursors (NO, NO2, NOx, CO and Total Volatile Organic Compounds (TVOC)) and their
interactions patterns. Four monitoring sites of different land habitats namely coastal Downtown
Vancouver, low undulated Industrial-commercial-residential mix (Burnaby), inland industrialcommercial-residential mix (Surrey) and Mountain based urban (Chilliwack) sites were selected
for analysis.
Trend and status (both seasonal and diurnal) of ozone and its precursors were done. Despite
relatively higher concentrations of NOx and TVOC, coastal site (Downtown) experience
relatively lower level of ozone than the other urban sites indicating possible meteorological
effects on the precursor movements and variations in ozone deposition/destruction rates in
different land habitats. It was found that both NO and NO2 influences with similar pattern on
ozone process in all sites while the influence of TVOC on ozone formation were found in the
inland sites only. Ozone production and destruction rates are highest in Chilliwack (1.97 ppb/hr
and 2.0 ppb/hr) and lowest in the downtown Vancouver site (1.11 ppb/hr and 1.15 ppb/hr).
Regression analysis shows that NO2/NO ratio plays significant influence on ozone level of all the
sites but varies with different land habitats (R2: 0.25 to 0.65) and with different season. However,
the influence of TVOC/NOx was insignificant in all sites (R2<0.1). Distinct interaction pattern
between ozone with the ratio of NO2/NO were observed in different land habitats. Seasonal
variations in interaction patterns show stronger relationships between the parameters in the
winter and weaker relationships in the summer indicating the possible topographical and
meteorological effects.
Key word: Surface ozone, Ozone precursors, Interaction Patterns, NO2/NO and TVOC/NOx
INTRODUCTION
Surface level ozone formation is a complex process that are contributed, under favorable
photochemical conditions, by the nitrogen oxide (NOx) and volatile organic compounds (VOC)
emitted from traffic vehicle, industrial activities, and household combustions ( Health Canada,
2002; Lu and Wang, 2003). Studies show that intensity of ozone production depends on the
availability of NO2 and the favorable photochemical conditions. Availability of NO2 again
depends on the rate of transformation of NOx , CO, and volatile organic compounds (VOC’s)
(Cooper and Alley, 2002；Sillman，1999). Ratio of NO2 and NO plays a vital role in stabilizing
the ozone level through production as well as destruction process (Health Canada, 2002; Lu and
Wang, 2003; Saito et al., 2002). Saito et al. (2002) found that ozone production level could be
related to the ratio of NOx and TVOC as TVOC could contribute in converting NO into NO2
without consuming O3. The ratio of NO2/NO at a certain location can be considered as an
indicator of the potential of ozone production. Higher ratio of NO2/NO indicates higher level of
ozone production and low ratio indicates the higher potential for ozone destruction by NO. On
the other hand, ratio of TVOC and NOx can influence the interaction patterns of ozone
production process and could be used as photochemical indicator to control peak ozone level at a
certain location (Cooper and Alley, 2002).
This study aims to investigate the interaction patterns of ozone with its precursors through
analyzing the pattern of NO2/NO, TVOC/NOx level, and correlations of ozone with these
photochemical indicators and precursors.
2.0
STUDY METHODS
2.1
Description of the areas under study
Since the emissions of ozone precursors like NOx (i.e. NO + NO2) and VOC’s (Methane and
non-methane) depends on the industrial activities and traffic volume, we have chosen one city
from each of the mentioned land habitat categories for investigation. Downtown Vancouver is
connected with Burnaby, Surrey, and Chilliwack through inter provincial Highway-1 and with
Richmond through Highway-99. These highways are extensively used by the daily commuters to
the Downtown Vancouver.
The Fraser Valley (FV) air shed contains the majority of the population of British Columbia
(more than 4 million) and continues to have a high population growth. Unique geographic
features and the growing large population, the interaction of urban, suburban, marine, and
agricultural emissions of pollutants cause air pollution that are frequented in the FV. As such,
surface ozone is on the air quality agendas of the public, planners and policy makers at all levels
of government.
Fraser Valley is bounded by the Coast Mountains in the north, the cascades mountains in the
Washington state of the USA in the south, and the Pacific Ocean in the west. Presence of
cascades of mountains causes the air masses trapped into the Fraser basin when wind travels
towards the mountains. Fraser valley region has a relatively mild climate with low to moderate
winds. The prevailing wind directions are dominated by airflow towards the north and north
easterly directions. Besides, the wind directions are associated with the see breezes which occur
during the middle of the day.
2
Figure 1: Maps showing Fraser Valley and the Approximate Locations of the Selected
Monitoring Sites
2.2
Physical and Chemical Transformation Between Ozone and Precursors
Interaction between ozone and precursors is mainly dominated by the production of secondary
pollutant called NO2 which subsequently undergoes photolytic reaction to produce ozone.
However the production of NO2 in the atmosphere can be made by NO at the expense of
available ozone or by reactive volatile organic compounds without destructing available ozone.
However, chemistry of ground level ozone goes through a complex process of production and
destruction cycle. Anthropogenic (traffic, industrial process etc.) and biogenic sources emits
nitric oxide and VOCs that are believed to undergo following major chemical reactions (Health
Canada, 2000; Lu and Wang, 2003; Cooper and Alley, 2002) to produce NO2:
(i)
(ii)
(iii)
NO + O3 ---- NO2 + O· …………………………………………R1
NO2 + Sunlight absorption (hυ) (λ< 4300 Å) -- NO + O· …………R2
O2 (+M) + O· ---------- O3 (+M) …………………………………..R3
Volatile Organic Compound (VOC) contributes in the recycle of NO2 required for ozone.
(iv)
(v)
(vi)
(vii)
(viii)
RH + OH· ---- R· + H2O ………………………………………. R4
R· + O2 (+M) -- ROO· + M …………… ………………………R5
ROO· + NO ---------- RO· + NO2 ………………………………..R6
RO· + O2 (+M) ---------- RCHO + HO2· ………………………...R7
HO2· + NO ---------- NO2 + HO· ………………………………...R8
Amount of ozone in a certain time and location, as shown in the cycle of reactions (R1 to R3),
depends on the ratio of NO2 and NO in the air and also on the availability of these two
compounds. As shown in the above reactions (R4 to R8), one VOC molecule could contribute
two molecules of NO2 upon availability of hydroxyl ions which may be found in the polluted
atmosphere. While variations in the ratio of NO2 and NO effects the stability in ozone level,
variations in the ratio of VOC and NOx could influence the quantity of ozone level.
3
2.3
Data Gathering and Analysis
GVRD provided the ambient air quality data of the selected monitoring stations and all the data
were received as hourly mean concentration. We received ambient data on all the criteria air
pollutants including NO2, NOx, O3, and Total VOC. However, TVOC data are collected by
GVRD on irregular basis and total number of TVOC data was also small compared to other
pollutants. We have chosen data between the periods of 1988-2002 for this study. The raw data
has been further analyzed statistically to derive aggregated diurnal, monthly, seasonal and annual
values. Regression analysis of the aggregated values was done for interactive characteristics
analysis between Ozone and NOx and VOC’s.
3.0
RESULTS AND DISCUSSION
3.1
Temporal Pattern of Ozone and its Precursors
Annual mean values of ozone and precursors pollutants have been plotted for the period of 19932002 to examine the pollution trend as shown in the Figure 2. Results show that amongst the
selected sites, highest level of ozone and lowest level of NO, NO2, NOx, and TVOC existed in
the mountain based city of Chilliwack. While lower level of ozone but higher level of precursor
pollutants was found at the Downtown Vancouver where emissions of precursor pollutants from
traffic, commercial heating systems contributes to the added level of precursors. Ozone and its
precursor levels at the Surrey and Burnaby follows the levels found at Chilliwack. In the inland
urban city of Burnaby level lies between the levels found at Chilliwack and Downtown
Vancouver. Net changes in the ozone and precursors levels over the mentioned period are shown
in the Table 1. As shown in the Table 1, despite the decreasing trend in all the precursors like
NO, NO2, NOx and TVOC, ozone level has been found in increasing trend in all the sites. In the
case of TVOC, Burnaby site experiences increase in the TVOC level perhaps due to
contributions from the petroleum refinery site located in the area.
Table 1: Net percentile changes (%) in the trend in ozone and its precursors levels
Land Habitat Types / Site
NO
NO2
NOx
TVOC
Downtown Vancouver (DTN)
-44.09
-13.35
-33.83
-14.69
Burnaby S. (BBY)
-25.20
-17.84
-19.50
12.69
Surrey E. (SRY)
-35.45
-18.61
-27.99
-15.46
Chilliwack (CWK)
-21.09
-5.22
-12.69
-25.46
Ox
42.17
18.02
34.35
16.83
As regards to the trend in the ozone and its precursors in the selected sites, there is a contrasting
difference between the downtown site and Chilliwack. For example net percentile reduction in
NO, NO2, & NOx is highest in Downtown while the lowest net percentile reductions were
observed in Chilliwack for the same pollutants and vice versa is the trend in the case of ozone
pollution.
4
35
70
30
160
25
140
120
20
100
15
80
60
10
40
5
20
TVOC
NO
NOx
NO2
O3
0
0
1993
1994
1995
1996
1997
1998
1999
2000
2001
Fig. 2b. Annual Trend of Ozone and Precursors at Surrey
Mean Level of NO, NO 2 , NOx, O3 (ppb) and TVOC (ug/m3)
Fig. 2a. Annual Trend of Ozone and Precursors at Downtown Vancouver
180
Mean Level of NO2 and O3 (ppb)
Mean Level of NO, NOx(ppb) and TVOC
(ug/m3)
200
60
50
40
30
20
10
NO
1993
1994
1995
(a). Downtown Vancouver
Fig. 2c. Annual Trend of Ozone and Precursors at Burnaby
Mean Level of NO, NO 2 , NOx, O3 (ppb) and TVOC (ug/m3 )
Mean Level of NO, NO2, NOx, O3 (ppb) and TVOC (ug/m3)
70
60
50
40
30
20
10
NO2
NOx
O3
T VOC
0
1993
1994
1995
1996
1997
1998
1999
2000
1996
1997
NOx
O3
1998
1999
T VOC
2000
2001
2002
2001
2002
(b) Surrey
70
NO
NO2
0
2002
2001
2002
Fig. 2d. Annual T rend of Ozone and Precursors at Chilliwack
60
50
40
30
20
10
NO
NO2
NOx
O3
T VOC
0
1993
1994
1995
1996
1997
1998
1999
2000
(c) Burnaby
(d) Chilliwack
Figure 2: Trend of Annual Mean Level of Ozone and Its Precursors at (a) Downtown Vancouver,
(b) Surrey, (c) Burnaby, and (d) Chilliwack
3.2
Interaction Patterns of ozone and its Precursors
3.2.1
Diurnal Variations in Ozone and Precursors
Figure 3 shows the typical pattern of diurnal variations of ozone and precursors at the different
land habitat sites. As regards to ozone level, an increase in day time and decrease in night were
observed in all the sites of different land habitat types. Peak level of ozone also appeared almost
at the same time of the day (15.00 hr) in all sites implying that ozone peak level reached due to
local photochemical processes and ozone lean levels are reached in the late morning. Peak level
of NO, NO2, NOx and TVOC were found both in the morning contributed mainly by the traffic
rush hours. Distinct afternoon lean and late afternoon peak level for precursors were found at
about 14:00 hr and 22:00 hrs respectively in all the sites except downtown Vancouver while such
distinct afternoon lean and peak period were not occurred at coastal sites of Downtown
Vancouver rather several small lean and peak levels occurred perhaps contributed by the
relatively higher volume of traffic all day long. Peak level of NO, NO2 and NOx were occurred
almost simultaneously. However, morning peaks of precursors level generally follows a time
progression starting at about 6:00 hrs at Chilliwack, and finishing at 08:00 hrs at the downtown
Vancouver as huge volume of traffic commutes to the downtown areas using the Trans Canada
Highway-1 and passes sequentially through the cities of Langley, Surrey, Burnaby respectively.
Diurnal variations in the ratio of NO2 and NO follow a distinct pattern during the whole day and
also show a relationship with the ozone variations. NO2/NO ratio reaches at the minimum level
5
during the morning traffic rush when maximum level of NO emitted from the traffic and
photochemical process begins. However, the value of the ratio starts increasing along with the
consumption of NO2 due to its photochemical conversion into oxidants (Ox) as well as
simultaneously lesser amount of emission of NO from the traffic lean period (11:00 to 17:00 hr).
As the ozone production level starts decreasing after the late afternoon, NO2 level starts building
up and the ratio reaches to the peak level at the late night (21:00 hr) and continue at that level till
to 06:00 hr considered to be due to two reasons: (a) emission of NO from the evening traffic
rush and other industrial and commercial sources; (b) emitted NO undergoes through the
catalytic reaction process (in the polluted atmosphere) with the already produced ozone to
convert it again into NO2 and O2 (M).
Fig.3b. Diurnal Interaction Pattern Between Ozone and Precursors at Surrey
Fig. 3a. Diurnal Pattern Between Ozone and Precursors at Downtown Vancouver
72
30
1.00
NO
NO2
2.00
NO2/NO
1.80
0.90
52
0.70
0.60
42
0.50
32
0.40
0.30
22
0.20
Mean Value of O3, NO, NO2 (ppb)
25
0.80
Ratio of NO2 and NO
Mean Value of Ozone (O3), ppb
62
1.60
1.40
20
1.20
15
1.00
0.80
10
Ratio of NO2 to NO
O3
0.60
0.40
12
5
0.10
2
O3
0.00
0
1
2
3
4
5
6
7
8
NO
NO2/NO
0
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
T ime of the Day (0-23h)
0.20
0.00
0
1
2
3
4
5
6
7
8
(a) Downtown Vancouver
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
T ime of the Day (0-23h)
(b) Surrey
Fig 3c. Diurnal Interaction Pattern Between Ozone and Precursors at Chilliwack
30
NO2
1.80
Fig 3d. Diurnal Distribution of ozone and Precursors at Burnaby
30
1.80
1.60
1.20
1.00
15
0.80
10
0.60
0.40
5
O3
NO
NO2
NO2/NO
0
0.20
25
1.40
1.20
20
1.00
0.80
15
0.60
0.40
10
NO
0.00
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
T ime of the Day (0-23h)
Ratio of NO 2 and NO
20
Mean Level of NO, NO 2 , and O3 (ppb)
1.60
1.40
Ratio of NO 2 to NO
Mean Value of O3 , NO, NO2 (ppb)
25
NO2
O3
NO2/NO
5
0.20
0.00
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23
(
(d) Burnaby
Figure 3: Diurnal Pattern of Annual Mean Diurnal Level of Ozone and its Precursors (NO, NO2,
and NO2/NO). (a) Downtown Vancouver, (b) Surrey, (c) Chilliwack, and (d) Burnaby
(c) Chilliwack
T ime of the day (0-23h)
Peak value of NO2/NO ratio reaches first in the furthest site at Chilliwack at about 14:00 hrs and
gradually progresses to the sites closer to the Downtown Vancouver such as at Surrey at 13:00
hrs, Burnaby at 15:00 hrs and Downtown at 18:00 hrs. This phenomena indicates that the sites
closer to the downtown contributes significantly in precursors emission from industrial /
commercial sources in addition to the traffic emissions. Diurnal pattern of TVOC/NOx was not
analyzed due to inadequate data but daily mean level of these pollutants showed that Coastal
sites particularly in Downtown Vancouver observed higher level of both TVOC and NOx (mean:
141.56 ug/m3 and 80.79 ppb respectively) compare to the inland urban sites of Burnaby (62.27
ug/m3 and 36.04 ppb respectively) and Surrey (51.0 ug/m3 and 33.82 ppb respectively). On the
other hand, Chilliwack shows the lowest level of NOx (30.21 ppb) and TVOC (49.52 ug/m3)
perhaps due to less contribution from the traffic.
6
As regards to daily production and destruction of ozone in the selected sites, Highest production
as well as destruction rates occurred at Chilliwack (production: 1.97 ppb/hr and destruction: 2.0
ppb/hr) and lowest rate occurred in the downtown Vancouver site (1.11 ppb/hr and 1.15 ppb/hr
respectively). It reveals that more urbanized sites daily ozone production and destruction rates
are lower (i.e. Burnaby: 1.57 ppb/hr and 1.54 ppb/hr) than the less urbanized sites (Surrey: 1.82
ppb/hr and 1.74 ppb/hr). Besides, relatively more plants and mountainous topography of
Chilliwack also enhance the ozone deposition rate.
3.2.2 Seasonal Variations of Ozone and Precursors
There are distinct seasonal variations in the interaction pattern between ozone and precursors as
well as between the precursors themselves. In general, stronger correlations exist between the
parameters in the winter compared to the summer in all the sites although the degree of such
relationships differs between the sites. Higher NO2/NO ratio were observed in all the sites during
the spring season and lower in the winter considered due to higher level of NO emissions from
traffic and heating system. Table 2 shows the median values of the daily mean levels of ozone,
TVOC/NOx, and NO2/NO of different sites during different seasons. Maximum ozone level was
observed during the spring seasons irrespective of the sites and maximum median level of ozone
was observed in the Surrey and Chilliwack despites higher level of NO emission in the
downtown Vancouver indicating the transport of precursors to the distanced sites before being
converted into ozone. Higher ratio of TVOC/NOx during the summer and spring indicates higher
contribution of TVOC from biogenic and anthropogenic sources in ozone production process.
Significant correlations between TVOC and temperature indicate that higher temperature in
summer may cause higher level of TVOC.
Table 2: Median Values of the Daily Mean Levels of O3, TVOC/NOx, and NO2/NO
Sites
Parameters
Winter
Spring
Summer
Autumn
Downtown
Ox (ppb)
3.83
11.27
7.88
3.67
Vancouver
TVOC/NOx
2.40
2.68
2.78
2.75
(DTN)
NO2/NO
0.74
1.28
0.85
0.60
Burnaby
O3 (ppb)
11.96
20.13
15.0
8.71
(BBY)
TVOC/NOx
3.65
3.45
3.10
3.30
NO2/NO
1.96
2.74
2.14
1.28
Surrey
O3 (ppb)
15.25
23.92
18.75
11.27
(SRY)
TVOC/NOx
2.37
3.14
3.57
2.91
NO2/NO
2.34
3.41
2.92
1.54
Chilliwack
O3 (ppb)
12.60
20.75
16.46
9.33
(CWK)
TVOC/NOx
2.54
3.10
4.33
2.87
NO2/NO
1.63
2.75
2.0
0.86
3.2.3 Analysis of the Interaction Patterns
Interaction pattern between ozone and precursors as well as between the precursors has been
analyzed through linear regression analysis. Following sections presents coefficient of
determinations (R2) of the regression analysis of the aggregate daily mean level of ozone and its
precursors and its seasonal variations:
7
3.2.3.1 Interaction between Ozone and its Precursors
As regards to the correlations between ozone and its precursors, it was found that both NO and
NO2 and their ratio (NO2/NO) strongly influence the ozone production and destruction process
but the strength of such correlations varies with the land habitats. Coastal site of Downtown
Vancouver showed relatively higher correlations (R2=0.63) followed by the urban sites of
Burnaby (R2=0.56) and Surrey (R2=0.45) while mountain base urban city of Chilliwack showed
the lower correlations (R2=0.34). Except for the Downtown Vancouver, all other sites showed
non-linear relationships. Figure 4 shows the interaction pattern and relationship between ozone
and NO2/NO.
35
45
Fig 4a: Correlations betw een Ozone and NO2/NO at Dow ntow n Vancouver
Fig. 4c: Correlations betw een Ozone and NO2/NO at Chilliw ack
40
30
y = 8.31x - 0.22
R2 = 0.63
y = 5.14Ln(x) + 12.93
R2 = 0.34
35
25
O3 (ppb)
O3(ppb)
30
20
15
25
20
15
10
10
5
5
0
0
0.5
1
1.5
2
NO2/NO
2.5
3
3.5
0
4
0
5
10
(a) Downtown Vancouver
40
15
20
25
NO2/NO
(c) Chilliwack
Fig. 4b: Correlations betw een Ozone and NO2/NO at Burnaby
45
Fig. 4d: Correlations betw een Ozone and NO2/NO at Surrey
35
40
y = 6.73 Ln(x) + 9.96
R2 = 0.56
35
25
30
20
25
O3 (ppb)
O3:ppb
30
15
y = 5.85Ln(x) + 11.85
R2 = 0.45
20
15
10
10
5
5
0
0
5
10
15
20
25
30
35
40
45
50
NO2/NO
0
0
10
20
30
40
50
60
70
NO2/NO
(b) Burnaby
(d) Surrey
Figure 4: Regression Results between Ozone and NO2/NO. (a) Downtown Vancouver, (b)
Burnaby, (c) Chilliwack, and (d) Surrey
3.2.3.2 Interaction Pattern amongst Precursors
Strong correlations were found in all the sites between NOx and NO (R2 > 0.90). Correlations
between NOx and NO2 shows weaker relations at Downtown VN, and Chilliwack (R2 < 0.45)
and moderate correlations at Burnaby (R2=0.61) and Surrey (R2=0.71) indicating
disproportionate influence of NO and NO2 on ozone production or destruction cycle (Ref.
equation R1 to R3) or accumulations of precursors. Significant correlations also exists between
NOx and TVOC with relatively stronger coefficient of determinations in downtown and inland
urban sites (DTN: R2=0.50, BBY: R2 =0.65, and SRY: R2=0.27) compared to mountain-based
site of Chilliwack where no significant correlations (R2=0.04) exists. This reveals that
contribution of TVOC on the ozone production is higher in the more urbanized cities with higher
8
traffic density (Downtown, Burnaby etc.) and higher number of gasoline stations compared to
the less urbanized sites with characteristics of relatively less traffic (Chilliwack). Figure 5
presents the regression results between Nitrogen Oxide (NOx) and TVOC for different land
habitats.
200
160
Fig. 5a: Regression Result betw een NOx and TVOC at Dow ntow n Vancouver
180
Fig. 5c: Regression Result betw een NOx and TVOC at Surrey
y = 0.68x - 3.20
R2 = 0.37
140
y = 0.27x + 32.19
R2 = 0.42
160
120
140
NOx(ppb)
NOx(ppb)
100
120
100
80
80
60
60
40
40
20
20
0
0
0
0
50
100
150
200
TVOC (ug/m3)
250
300
350
20
40
80
TVOC (ug/m3)
100
120
140
160
(c) Surrey
(a) Downtown Vancouver
Fig. 5d: Regression Result betw een NOx and TVOC at Burnaby
100
80
Fig. 5 b: Regression Result between NOx and T VOC at Chilliwack
y = 0.44x - 0.53
R2 = 0.65
90
70
y = 0.18 x + 20.48
R2 = 0.04
80
60
70
NOx:ppb
50
NOx:ppb
60
400
40
60
50
40
30
30
20
20
10
10
0
0
0
0
10
20
30
40
50
T VOC:ug/m 3
60
70
80
90
100
25
50
75
100
125
150
175
200
TVOC: ug/m3
(d) Burnaby
(b) Chilliwack
Figure 5: Regression Results between Nitrogen Oxide (NOx) and Total Volatile Organic
Compounds (TVOC) at (a) Downtown Vancouver, (b) Chilliwack, (c) Surrey, and (d)
Burnaby
3.2.3.3 Seasonal Relationship in Interaction Pattern amongst Precursors
Regression analysis of the daily mean values of nitrogen oxides and hydrocarbon compounds
(TVOC) has been done based on the different seasons and for sites of different land habitat types.
Figure 4 shows the regression results between NO2 and NO with best line-fit for the winter and
summer seasons. Amongst the land habitat types, both inland urban site of downtown Vancouver
(winter: R2=0.66, summer: R2=0.54) and mountain-base urban site of Chilliwack show
logarithmic coefficient of determinations (winter: R2=0.35, summer: R2=0.21) than the inland
site of Surrey (winter: R2=0.43; summer: R2=0.00) and Burnaby (winter: R2=0.52; summer:
R2=0.00) sites.
Regression coefficients between NOx and NO show significantly strong relationships in the all
sites with slight variations in different seasons (R2 >0.60) indicating that dominant sources of
NO remains same all over the year. Significant relationship also exists in other two inland urban
sites of Burnaby and Surrey but there is a distinct variation in such relationship between different
9
seasons: higher coefficient of determination (R2 >0.60) in winter implying relative increase or
decrease of both NO2 and NO levels and lower coefficients in the summer (R2 < 0.30) indicates
disproportionate variations in the NOx components perhaps due to TVOC contributions (Eqn. R4
to R8) as supported by relatively high correlations between NOx and TVOC in the inland sites.
3.2.3.4 Seasonal Interaction Pattern between Ozone and Precursors
Regression results show strong seasonal effect on the interaction pattern between ozone and
NO2/NO in the inland urban sites of Burnaby and Surrey. Stronger correlations (winter: R2>0.50
and summer: R2 <0.15) between O3 and NO2/NO were observed in the inland urban sites that
indicates proportional contribution of both NO2 and NO in ozone production as well as
destruction process. On the other hand, despite significant correlations (0.36<R2<0.58), small
seasonal effects were observed in the Downtown Vancouver which supports that the site is
mainly precursor originator and contributes less in direct production and destruction of ozone.
However, insignificant correlations between O3 and NO2/NO in Chilliwack (R2<0.05) in all the
seasons indicate the effects of meteorological factors in the variations in ozone level in addition
to the precursors. Table 3 presents the coefficient of determinations (R2) for different seasons
and different land habitats.
Table 3: Correlations Relationship between Ozone and NO2/NO
Seasons
Downtown
Burnaby (BBY)
Surrey (SRY)
Vancouver (DTN)
Winter
R2=0.58
R2=0.67
R2=0.49
Spring
R2=0.54
R2=0.32
R2=0.27
2
2
Summer
R =0.45
R =0.15
R2=0.04
Autumn
R2=0.36
R2=0.68
R2=0.35
4.0
Chilliwack (CWK)
R2=0.28
R2=0.17
R2=0.05
R2=0.25
CONCLUSION
Characteristics of interaction pattern of ozone (O3) and precursors (NO, NO2, NOx, and TVOC)
in four different land habitat sites of Fraser Valley of BC has been discussed in this paper. The
results showed some interesting pattern in the distribution of ozone and its precursors in terms of
the trend, variations in concentration levels in different sites and in different seasons that
influences the interactions between ozone with its precursors. Ozone production/destruction
process is greatly influenced by the interactions between the precursors (e.g. NO-NO2, TVOCNOx) and strength of such interactions is dominant in the coastal site (Downtown Vancouver) as
well as Mountain-based city of Chilliwack. In all the sites, ozone interaction behavior is
significantly influenced by the variations in NO2/NO ratio but strength of such interactions varies
with seasons and with respect to land habitats. Small range in the ratios of NO2/NO in all the
sites (median range 2.45 to 5.0) indicates the similar dominant sources of precursors (e.g. traffic
emissions).
ACKNOWLEDGEMENTS
Authors acknowledge and thank JSPS for providing funds and Bioresources faculty of Mie
University for logistic supports in carrying out this study. We also thank Greater Vancouver
Regional Authority for providing atmospheric and meteorological data for the region.
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