Environ Monit Assess (2009) 151:127–141 DOI 10.1007/s10661-008-0255-0
Surface ozone and meteorological condition in a single year at an urban site in central–eastern China Wenpo Shan & Yongquan Yin & Jianda Zhang & Xia Ji & Xingyan Deng
Received: 20 November 2007 / Accepted: 29 February 2008 / Published online: 9 April 2008 # Springer Science + Business Media B.V. 2008
Abstract Surface ozone and some meteorological parameters were continuously measured from June 2003 to May 2004 at urban Jinan, China. The levels and variations of surface ozone were studied and the influences of meteorological parameters on ozone were analyzed. Annual and diurnal ozone variation patterns in Jinan both show a typical pattern for polluted urban areas. Daytime ozone concentrations in summer were the highest in the four seasons. However, during nighttime from 2100 to 0600 hours ozone concentrations in spring was higher than that in summer. Daily averaged ozone showed negative correlation with pressure and relative humidity and
W. Shan (*) College of Chemistry and Environmental Science, Hebei University, Baoding 071002, People’s Republic of China e-mail:
[email protected] Y. Yin : J. Zhang School of Environmental Science and Engineering, Shandong University, Jinan 250100, People’s Republic of China J. Zhang School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, People’s Republic of China X. Ji : X. Deng Shandong Environment Protection School, Jinan 250001, People’s Republic of China
positive correlation with temperature, total solar radiation, sunshine duration and wind speed during the study period. Further studies show that, solar radiation is a primary influence factor for the daytime variations of ozone concentrations at this site; transport of pollutants by wind could enhance the pollution at this site; precipitation has a significant influence on decreasing surface ozone. A multi-day ozone episode from 16 to 21 June 2003 was observed at this site. Surface meteorological data analysis and backward trajectory computation show that the episode is associated with the influence of typhoon Soudelor, attributing to both local photochemical processes and transport of air pollutants from southeastern coastal region, especially Yangtze River Delta region. Keywords Urban atmosphere . Photochemical pollution . Ozone variation . Meteorological factors . Jinan
Introduction Increasing tropospheric ozone (O3) concentrations have received extensive attention around the world because of its damage to human health and ecosystem (e.g. McLaughlin and Downing 1995; Kim et al. 2004; Karnosky et al. 2006). Among the four factors—meteorology, photochemistry, emis-
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sions, and deposition—that lead to accumulation of ozone in the troposphere, meteorological processes are very important, causing large day-to-night, dayto-day, season-to-season, and year-to-year variations. (Solomon et al. 2000). Surface ozone and related meteorological factors have been extensively monitored in the urban area of the northern hemisphere, especially in North America and Europe (Solomon et al. 2000; Bloomfield et al. 1996; Cox and Chu 1996). These studies have comprehensively analyzed the factors and processes affecting ozone formation and accumulation. Recent studies have shown that, rapid urbanization and developments of industry and transportation facilities in the past three decades have caused a series of severe problems related to air pollution. Particularly, increasing consumption of fossil fuels by vehicles and power plants in urban area resulted in increased emission of ozone precursors (NOx, VOCs, CO, etc.) into urban atmosphere. In addition, with the action of UV light from the sun, some major cities in China, such as Beijing, Shanghai, Jinan, Hong Kong, Guangzhou are faced with photochemical threat, and high ozone concentrations are frequently reported (Wang et al. 2007; Streets et al. 2007; Lu et al. 2002; Shan et al. 2006). There are three grades of air quality standards for surface ozone in Chinese National Ambient Air Quality Standard, all is for hourly averaged concentration. Grade 1 (0.16mg/ m3, about 80ppbv) is mainly set for areas deserving special protection, for example natural reservation zones, Grade 2 (0.20mg/m3, about 100ppbv) is mainly set for the common urban and rural area, and Grade 3 (0.20mg/m3, about 100ppbv, the same value as Grade 2) is set for some special industrial area. Jinan, a medium-sized provincial capital city in central–eastern China, like other rapidly developing cities in China, faces rapid urban expansion and development, as well as air pollution problems. In winter, when a great amount of coal is consumed for heating, the city often suffers from higher concentrations of SO2 and particulate than the permissible values, especially when the weather conditions are unfavorable for the dispersion of air pollutants (Liu et al. 2007; Zhao et al. 2006). In recent years, with the rapid increase in the amount of motor vehicles, higher surface ozone concentrations than permissible value (100ppbv) were often observed in the urban area of Jinan, especially in summer (Du et al. 2007; Yin et al. 2006).
Environ Monit Assess (2009) 151:127–141
Ozone tendency in urban area is greatly impacted by the variations of meteorological condition and precursor concentrations, and the detection of ozone trends is central in evaluating the effect of precursor emission control programs. In this study, we present measurements of surface ozone and meteorological factors (temperature, pressure, total solar radiation, sunshine duration, relative humidity, wind direction, and wind speed) in the urban area of Jinan during a single year from June 2003 to May 2004. Based on the observational data, the levels and variations of ozone were characterized and the influences of meteorological conditions on ozone were analyzed.
Study site and techniques This study was conducted in Jinan, the capital of Shandong Province, with an urban population of 2.7 million and an urban built-up area of 190km2 in 2003. Located in central–eastern China, Jinan has a typical warm-temperate, semihumid, continental monsoon climate and well-defined four seasons. The average annual temperature is 14°C, and average annual rainfall is 650–700mm. There are complex reasons for the air pollution of Jinan, which is in a basin location, surrounded by mountains and the Yellow River embankment. Special terrain in this region makes air pollutants in the urban area of Jinan difficult to disperse. In addition, many major industrial pollutant sources of Jinan are located in the prevalent wind directions of the urban area, which aggravates the pollution of regional atmosphere. Measurements were carried out on the campus of Shandong University (36°42′ N, 117°08′ E, 34.5masl), which is in the eastern area of Jinan, lying in the second ring road (see Fig. 1). Ozone was continuously measured using a UV photometric analyzer (Thermo Environmental Instruments, model 49C), based on the absorption of ultraviolet radiation by ozone at 254nm as the principle. The limit of detection is 2ppbv and the precision is ±2ppbv. The instrument was operated continuously, every day for 24h. The interval of each measurement was 1min and the data presented in this paper are hourly and daily averaged values. Air samples were collected through Teflon inlet tubes, with a particulate filter to prevent the entry of particles into the instrument. The instrument was
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Fig. 1 A map showing locations of Jinan (36°32′–36°51′ N, 116°49′–117°14′ E), the observational site (Shandong University), and major air pollution sources (power plants, petrochemical plants, plastic factories, and steelworks) in Jinan
checked automatically every day by scrubbed ambient air (TEI, model 111) and with a span standard generated in a multi-gas calibrator (TEI, model 146). The height of the air intake was 8.5m above the ground. Several meteorological parameters, including temperature, pressure, total solar radiation, sunshine duration, relative humidity, precipitation, wind direction, and wind speed, were synchronously measured at the site using automatic meteorological instrument by Jinan Meteorological Administration, and we got the meteorological data from China Meteorological Data Sharing Service System (http://cdc.cma.gov.cn/). An Internet-based model of Hybrid Single-particle Lagrangian Integrated Trajectory (HYSPLIT, Version 4.8) was used to calculate backward trajectories in some high ozone days. The model was developed by the National Oceanic and Atmospheric Administration (NOAA) Air Resource Laboratory (http://www. arl.noaa.gov/ready/hysplit4.html). The meteorological input for the trajectory model was the FNL dataset (reprocessed from NCEP Final Analysis data by ARL). Each backward trajectory was calculated for 48-h durations (i.e., 2days) with 100magl vertical levels and 6-h label intervals (0000, 0600, 1200, 1800 hours UTC; i.e. 0800, 1400, 2000, 0200 hours local time).
Results and discussion Statistical characteristics of ozone variations The ozone concentrations in Jinan were statistically analyzed by hourly, daily, monthly and seasonal levels during a single year from June 2003 to May 2004. Table 1 shows some statistical characteristics of the hourly averaged ozone concentrations in each season of the year, as well as the percentages of exceeding the Chinese National Ambient Air Quality Standard Grade 2. The mean concentrations of ozone in different seasons follow the order of summer>spring> autumn>winter. Except winter, other seasons all presented several ozone values exceeding the Chinese National Ambient Air Quality Standard Grade 2. Most exceeded values were observed in summer, which indicates that photochemical pollution in Jinan is serious in summer and spring, especially in summer. In addition, levels of ozone precursors are also very high during summer in Jinan. For example, NOx and CO concentrations are about 20–30 and 1,500– 3,000ppbv respectively. There is a clearly variation tendency of daily averaged ozone concentrations in the study period of a year,
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Table 1 Statistical results of observed ozone concentrations according to seasons at Jinan from summer 2003 to spring 2004 Season
Mean (ppbv)
Median (ppbv)
Maximum (ppbv)
PEC (%)
n
Summer 2003 Autumn 2003 Winter 2003 Spring 2004 Total
43.39 22.13 14.34 38.35 29.55
37.85 13.47 9.32 37.66 22.38
138.65 106.06 62.12 131.42 138.65
5.3 1.5 0 0.5 1.8
2,070 2,032 2,177 1,982 8,261
PEC percentage of hourly averaged ozone concentrations exceeding the Chinese National Ambient Air Quality Standard Grade 2 (hourly average concentration 0.20 mg/m3 , about 100 ppbv)
tration started increasing rapidly coinciding with the increase of solar radiation from early morning to afternoon, reaching the peak value at 1300–1500 hours, and then continuously decreased until 2000 hours. Ozone levels were observed to be relatively steady and low at night, as there was no photooxidation of precursors causing ozone formation. However, from 0300 hours the values continuously decreased at a low rate. The loss of ozone is attributed to in situ destruction of ozone by the well-known reaction between ozone and NO, and the surface deposition. Ozone maintained a relatively low value in nighttime, and the minimum value in the day appeared during early morning hours, near sunrise (0500–0700 hours). Chemical loss of ozone by nitrogen oxides, as well as meteorological factors (zero solar radiation, low temperature, light wind, development of a nocturnal inversion layer, etc.) is one reason for the low levels of ozone in the early morning.
despite some fluctuations (see Fig. 2). Ozone presents a maximum level in summer (June 2003) and a minimum in winter (December 2003). This variation pattern is almost the typical mode that observed at big cities in the Northern Hemisphere. But the summer maximum of ozone in Jinan is just contrary to some cities under the impact of summer monsoon, such as Hong Kong and Thumba, where are dominated by summer minimum (Wu and Chan 2001; Nair et al. 2002). In general, ozone variation over the diurnal scale can provide insight into the interplay of emissions, and chemical as well as physical processes that operate on a diurnal cycle. A clear diurnal cycle of ozone can be seen from Fig. 3, which shows the diurnal statistics including maximum, mean, median, minimum, 1–99%, 5–95%, and 25–75% of the data for each hour. The diurnal variation of ozone in Jinan shows a typical pattern for polluted urban areas. Ozone concenFig. 2 Daily mean, daily maximum, and monthly mean ozone concentrations from June 2003 to May 2004 (local time)
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Persistent high ozone episodes
Daily mean Daily maximum Monthly mean
120
Ozone / ppbv
100 80 60 40 20 0 7/30/2003
9/28/2003 11/27/2003 1/26/2004
Date
3/26/2004
5/25/2004
Environ Monit Assess (2009) 151:127–141 Fig. 3 Diurnal variations of ozone concentrations from June 2003 to May 2004 (local time)
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180
max 99% O mean 1% min box 25~75% whisker 5~95% line median
Ozone / ppbv
150 120 90 60 30 0 0:00
04:00
Average diurnal variations of ozone concentrations for each season from summer 2003 to spring 2004 are presented in Fig. 4. Ozone diurnal variation of each season showed a similar pattern, but the magnitudes of variations were different. Daytime hourly averaged ozone concentrations showed significant seasonal
Fig. 4 Diurnal variations of ozone concentrations according to seasons from summer 2003 to spring 2004 (local time)
70
08:00
12:00 Hour
16:00
20:00
differences with a clear order of summer>spring> autumn>winter. However, ozone concentrations during nighttime from 2100 to 0600 hours in spring were higher than that in summer. Daytime high ozone concentration in summer, due to favorable meteorological conditions has aroused great interest in the
03'Summer 03'Autumn 03'Winter 04'Spring
60
Ozone / ppbv
50 40 30 20 10 0
0:00
04:00
08:00
12:00 Hour
16:00
20:00
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Meteorological effects
study of photochemical pollution at urban areas (e.g. Vautard et al. 2005; Cristofanelli et al. 2006; Syri et al. 2001). Some studies have suggested that the annual variation of stratospheric–tropospheric exchange might be the major factor in contributing to the widely observed ozone spring maximum in mid-latitudes of Northern Hemisphere, although there are still many debates as to the origins of this phenomenon (Monks 2000). It is well known that ozone is maximum in the free troposphere at the hemispheric scale in spring. The observed nighttime high ozone concentration during spring may be due to the influence of stratospheric–tropospheric exchange, which needs further studies to testify. Also, impacts from maritime air masses and higher nighttime ozone loss rate in summer may be important reasons for lower nighttime levels of surface ozone in summer. The frequencies of the hours in which the daily maximum ozone concentrations in each season appeared are shown in Fig. 5. Daily maximum ozone concentrations mostly appeared in 1200–1600 hours during the study period from summer 2003 to spring 2004, accounting for about 70%. The frequencies of the time in which daily maximum ozone concentrations in 24h appeared show a two peaks type, one peak appeared in the daytime, while another appeared in the nighttime. Fig. 5 Frequencies of the hours appeared daily maximum ozone concentrations in the four seasons from summer 2003 to spring 2004 (local time)
Day to day variations of ozone and meteorological parameters Meteorological conditions play an important role in ozone formation, transfer and dispersion. Variations of local meteorological conditions, such as solar radiation, temperature, wind direction, wind speed and relative humidity, can greatly affect the temporal variations of ozone. Therefore, analysis of the influences of meteorological parameters on ozone is very helpful to the better understanding of local and regional occurrence of ozone pollution. Daily summaries, as the basis of most recent statistical assessments of trend, are appropriate in view of the time scales of meteorological impact on ozone, which is on the order of days (Thompson et al. 2001). Time series of daily averaged ozone concentrations and total solar radiation, sunshine duration, relative humidity, temperature and pressure over the study period at Jinan are shown in Fig. 6. Variations of daily averaged temperatures showed a similar pattern to ozone concentrations characterized by high values during summer and low values during winter, while variations of pressure showed a contrary pattern. This relationship among ozone concentration,
20 18
03'Summer 03'Autumn 03'Winter 04'Spring
Frequency / %
16 14 12 10 8 6 4 2 0 0
2
4
6
8
10
12
Hour
14
16
18
20
22
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SR /MJ m
-2
30
.
20 10 0 15
SD/ h
Fig. 6 Time series of daily averaged ozone concentrations and meteorological parameters at Jinan from June 2003 to May 2004 (local time). SR total solar radiation, SD sunshine duration, RH relative humidity, T temperature, P pressure
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10 5
RH/%
0 100 80 60 40 20 0
T /°C
30 15 0 -15
P /Pa
10200 10050 9900
O3 /ppbv
9750 100 50 0 7/30/2003 9/28/2003 11/27/2003 1/26/2004 3/26/2004 5/25/2004
Date temperature, and pressure could be explained on theoretical grounds. Temperature plays an enhancing role in the propagation rate of the radical chains, and has an opposite effect on the termination rate of these chains (Tu et al. 2007). Therefore, high temperature can facilitate the production of ozone. During the study period, daily variations of both daily average and maximum temperature showed significantly positive correlation with ozone average and maximum concentrations, with the correlation coefficient of 0.68 and 0.80 respectively, see Fig. 7a and g. The observed pressure was controlled by large-scale pressure systems (High or Low), and the negative correlation
of temperature and pressure was the co-product of such synoptic-scale features. As many previous studies presented, humidity is also important because it may play a role in the overall reactivity of the atmosphere, by affecting chain termination reactions and the production of wet aerosols which in turn affect the ultraviolet actinic flux (Camalier et al. 2007). In this study, daily variations of relative humidity values show an insignificantly negative correlation with ozone concentrations in the study period of a year, with the linear correlation coefficient just is −0.25, but a significant negative correlation in summer 2003, with a correlation coefficient of −0.84.
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b
a 120
120
[O3] = 10.28 + 1.32 T R = 0.68
80 60 40
60 40 20
0
0
-5
0
5
10
15
20
25
30
R = − 0.66
80
20
-10
[O3] = 1433.96 − 0.14 P
100
Ozone / ppbv
Ozone / ppbv
100
9750 9800 9850 9900 9950 10000 10050 10100 10150
35
Temperature / °C
Pressure / Pa
c 120
d 120 [O3] = 11.28 + 1.65 SR R = 0.63
80 60 40
R = 0.40 80 60 40
20
20
0
0
0
5
10
[O3] = 17.35 − 2.01 SD
100
Ozone / ppbv
Ozone / ppbv
100
.
15
20
25
0
30
2
-2
Solar Radiation / MJ m
e 120
6
8
10
12
14
f 120
[O3] = 42.18 − 0.22 RH
100
100
Ozone / ppbv
R = − 0.25
80 60 40
40
0
0 15
30
45
60
75
90
R = 0.38
60
20
0
[O3] = 11.83 + 5.01 WS
80
20
0
2
Relative Humidity / %
4
140
[DMO3] = 10.89 + 2.24 DMT
120
R = 0.80
100 80 60 40 20 0 -10
6
.
Wind Speed / m s
g Daily Maximum Ozone / ppbv
Ozone / ppbv
4
Sunshine Duration / hour
0
10
20
30
Daily Maximum Temperature / °C
40
8 -2
10
Environ Monit Assess (2009) 151:127–141 Fig. 7 Liner correlation analysis of daily averaged ozone concentrations and meteorological parameters (a–f), as well as daily maximum ozone concentrations and temperatures (g), from June 2003 to May 2004
In order to analyze the relationships between ozone concentration and individual meteorological parameter, we performed a linear correlation analysis. Analysis result for daily averaged ozone concentrations and meteorological parameters are shown in Fig. 7. We can see that, Ozone showed negative correlation with pressure and relative humidity and positive correlation with temperature, total solar radiation, sunshine duration, and wind speed. The significant impact factors for ozone were temperature, pressure, and total solar radiation. Influence of solar radiation Generally, ozone is formed primarily through the action of UV light, hence it would be expected that daily averaged ozone concentration correlated well with solar radiation and the diurnal variation of ozone concentration closely follows solar radiation. Because of the instrument problems, we only got the total solar radiation data for June–October 2003 and February– March 2004, so we present sunshine duration in Fig. 6 as an added parameter of solar radiation. According to the analysis, daily total solar radiation values show significant positive correlation with daily averaged ozone concentrations. The linear correlation coefficient is 0.63.
Hourly variations of ozone concentrations and total solar radiation values during daytime in July 2003 and February 2004 are presented in Fig. 8. It can be seen that, the varying tendency of hourly averaged ozone concentrations was consistent with total solar radiation, though it was delayed for several hours. The delayed time was about 1h during forenoon and 3h during afternoon for July 2003, and about 2h during daytime for February 2004. So we calculated the linear correlation between total solar radiation from 0500 to 1200 hours and ozone concentrations from 0600 to 1300 hours, total solar radiation from 1200 to 1800 hours and ozone concentrations from 1500 to 2100 hours in July 2003, and total solar radiation from 0600 to 1700 hours and ozone concentrations from 0800 to 1900 hours in February 2004. The result shows a significant correlativity between these two parameters. The correlation coefficients are 0.996, 0.995, and 0.981 respectively. This suggests that solar radiation is one of the most significant influences on the daytime variations of ozone concentrations at this site. Influence of wind Wind is one of the most important processes for the transfer and dispersion of air pollutants. Rising in wind speed often implies the rising in transport of primary pollutants, and which may results in lower pollutant concentrations. However, the function of this process is much more complex for secondary pollutants. From Fig. 7 we can see that, ozone shows
4
50
3
40
2
30
1
20 6:00
8:00 10:00 12:00 14:00 16:00 18:00 20:00
.
Total solar radiation / MJ m
-2
5
February 2004 1.5
Ozone SR
35 30
Ozone / ppbv
60
July 2003
.
Ozone SR
6
Total solar radiation / MJ m
70
-2
b
a
Ozone / ppbv
R
135
1.0
25 20
0.5
15 10
0.0
0
7:00
9:00
11:00
13:00
15:00
17:00
19:00
Hour Hour Fig. 8 Hourly variations of ozone concentrations and total solar radiation values during daytime in July 2003 (a) and February 2004 (b) (local time)
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weak positive correlation with wind speed. Higher wind speed often leads to lower NO, and therefore the loss of ozone is reduced. On the other hand, high wind often comes from the direction of highly polluted areas of the city (see Fig. 9), so the transport of ozone and precursors from these areas may be another reason for the positive correlation between ozone and wind speed. In addition, long-range transport of air pollutants to Jinan caused by high wind may be a reason for the positive correlation as well. Wind from S–WSW often led to high ozone levels (see Fig. 10), and the wind speed for these directions often was high (see Fig. 9). Considering the geographical location of Jinan, long rang transport of air masses from south associated directions might bring more pollutants from higher industrialized and urbanized southern region than northern region to Jinan, and due to the influence of marine air masses from the eastern region, winds from the southwest directions are associated with higher ozone concentrations than southeast. Influence of precipitation Time series of daily averaged ozone concentrations and daily total precipitations are shown in Fig. 11. It can be seen that, when precipitation appeared ozone concentration decreased sharply. This may be due to the precipitation scavenging function on ozone precursors, low solar radiation during precipitation days, and humidity increase around precipitation process. 0
10 8
Wind Speed/m s
-1
.
N 315
45
6 4 2 0 270
90
2 4 6 8 10
225
135 180
Wind Direction / ° Fig. 9 Wind speed according to directions from June 2003 to May 2004
Particularly, we analyzed the influences of precipitation on ozone during a frequent precipitation period from 4 July to 9 September 2003, in which precipitation days were almost equal to non-precipitation days. Ozone concentration data were identified according to precipitation and non-precipitation days and then compared. The result suggests that, averaged ozone concentration in precipitation days is 27.1ppbv, and in non-precipitation days is 38.8ppbv. Precipitation has a significant influence on the decrease of surface ozone. Meteorological characteristics of a multi-day ozone episode In this study, persistent high ozone episodes were observed from 16 to 21 June 2003 (see Fig. 2). Particularly, from 17 to 20 June all daily averaged ozone concentrations exceeded 90ppbv, and each day the Chinese National Ambient Air Quality Standard was exceeded by more than 10h. These 4days were the highest ozone value days during the study period. For better understanding of the meteorological effects on this multi-day ozone episode, surface meteorological data and backward trajectories were analyzed Surface meteorological condition analysis As found in many previous studies, certain meteorological conditions, including intense solar radiation, high temperature, light wind, and minimum rainfall, are required in the formation of high ozone levels. During the episode days, a typhoon names Soudelor moving along the eastern coast of China and passed by the eastern marine region of Jinan, and influenced the regional meteorological condition. Some studies have shown that tropical storm could cause regional ozone episode in the vicinal area by influencing meteorological condition and transport of pollutants. For example, all six territory-wide ozone episodes occurred in the summers of 1994–1999 in Hong Kong were found to be related to the influence of tropical storms (Lee et al. 2002). We analyzed the surface meteorological conditions of Jinan during the episode days (see Table 2), and some characteristics stand out: (1) Persistent high temperature with daily averaged temperatures all exceeded 25°C and daily maximums all exceeded 30°C, which facilitated the production of ozone by its effects on the reactions of radical chains; (2) Relative
Environ Monit Assess (2009) 151:127–141 Fig. 10 Averaged ozone concentrations according to wind directions from June 2003 to May 2004
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40
Ozone / ppbv
30
20
10
0 N
NE
humidity was constantly low during this period; (3) Meteorological conditions in 16 June shows some differences with that in other days, such as intenser solar radiation, longer sunshine duration, lower wind speed, and northern wind direction, more favorable for photochemical pollution; (4) Short sunshine
Fig. 11 Time series of daily averaged ozone concentrations and daily total precipitations at Jinan, from June 2003 to May 2004 and from 4 July to 9 September 2003 (local time)
Precipitation Ozone
E
SE S Wind Direction
SW
W
NW
durations in 19 and 21 June and some daily maximums appeared in nighttime both indicate that there were other main reasons for this multi-day episode besides local sources; (5) Continuously high wind from S–SW from 17 to 21 June indicates that horizontal transport might be a important reason for these episodes; (6)
100
60
80 40
60 40
20
20 0
0 7/13/2003 7/23/2003 8/2/2003 8/12/2003 8/22/2003 9/1/2003
120 100
80
80
60
60 40
40
20 0
20 0 7/30/2003 9/28/2003 11/27/2003 1/26/2004 3/26/2004 5/25/2004 Date
Ozone / ppbv
Precipitation / mm
100
138
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Table 2 Ozone concentrations and meteorological conditions observed during a multi-day ozone episode from 16 to 21 June 2003 Date
O3 (ppbv)
Hours
Time
T (°C)
P (Pa)
SR (MJ·m−2)
SD (h)
WS (m·s−1)
WD
RH (%)
RF (mm)
16 17 18 19 20 21
50.7 108.1 107.8 100.7 94.6 64.1
2 14 17 18 10 1
1700 1700 1600 2300 0000 1100
25.0 28.4 29.6 30.2 32.1 30.2
9,913 9,890 9,846 9,818 9,830 9,856
27.54 18.18 20.6 – – –
11.8 8.3 7.4 4.3 10.3 4.5
2.5 (4.6) 5.3 (7.4) 5 (10.3) 3.8 (7.1) 6.3 (8.9) 4.3 (7.7)
N SW S S S SSW
44 39 38 38 32 40
0 0 0 0 0 0
June June June June June June
(102.0) (138.7) (135.0) (136.0) (130.2) (107.7)
(32.2) (33.4) (35.7) (35.6) (37.5) (34.1)
Values in parenthesis are the daily maximums. Hours hours exceeding the Chinese National Ambient Air Quality Standard Grade 2 (hourly average concentration 0.20 mg/m3 , about 100 ppbv), Time the local time when daily maximum ozone value appeared, T temperature, P pressure, SR total solar radiation, SD sunshine duration, WS wind speed, WD wind direction, RH relative humidity, RF rainfall
Zero rainfall during this period also is an important reason for persistent high ozone. After persisting for 6days, this multi-day episode was terminated by a 62mm rainfall in 22 June. Backward trajectory analysis To examine the effects of air mass transport on this multi-day episode, back trajectories before (13–15 June), during (16–21 June), and after (22–24 June) the multi-day episode were computed and analyzed (Draxler and Rolph 2003). Figure 12 illustrates the backward trajectories for these days with the ending time of each trajectory being 0900 hours UTC (1700 hours local time) when most maximum hourly ozone was observed during this episode. During the multi-day episode, backward trajectories were under the influence of typhoon Soudelor. Trajectory for 16 June came from northeast marine region, so the air mass might be relatively clean. However, favorable meteorological condition (long sunshine duration, intense solar radiation, warm temperature, and low wind speed) for ozone production and accumulation caused 2h ozone exceeding 100ppbv in the afternoon. During 17 June, with typhoon Soudelor moving close to southeast China, the direction of the trajectory ending at the site regularly changed from east to south. From 18 to 21 June, trajectories of air mass all originated from the lower atmosphere of highly industrialized and urbanized southeastern coastal region of China, and ended at the site from S–SE directions. Many studies have shown that, ozone and its precursors transporting from this region, especially from Yangtze River Delta
region often enhance ozone concentrations in the surrounding areas (Wang et al. 2006; Tu et al. 2007). According to our studies about the trajectories ended at Jinan in the study period of a year, more than 30% ozone episodes in Jinan are associated with trajectories originating from or passing by this region (not shown). Therefore, high ozone values in these days, especially high ozone values in the night of 19 and 20 June, might be associated with the transport of air pollutants from severe polluted region. Before this episode, the trajectories originated from different locations in the north of the study site, and passed distinctly different paths before reaching the site. After this episode, the trajectories turned back from south to north rapidly. Though the trajectory for 22 June originating from the highly industrialized and urbanized areas of the Yangtze River Delta might took plenty air pollutants, a rain during the daytime terminated this multi-day episode. Therefore, this episode is associated with the influence of typhoon Soudelor, attributing to both local photochemical processes and transport of air pollutants from southeastern coastal region, especially Yangtze River Delta region.
Conclusion In this study, we present the observational data of near surface ozone and some meteorological parameters from June 2003 to May 2004, in the urban area of Jinan, China. The obtained ozone values indicate that photochemical pollution in Jinan is serious, especially in
Environ Monit Assess (2009) 151:127–141
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Fig. 12 The 48-h backward trajectories of air masses (b) before, (a) during, and (c) after the multi-day episode
late spring and summer. Ozone levels in different seasons follow the order of summer>spring>autumn> winter, and the annual variation pattern is almost the typical mode of big cities in the Northern Hemisphere. The diurnal variation of ozone in Jinan shows a typical pattern for polluted urban areas, characterized by high levels during noon or afternoon, low levels during late
night or early morning, and big variation magnitude between daytime and nighttime. Daytime ozone concentrations in summer were the highest in the four seasons. However, during nighttime from 2100 to 0600 hours ozone concentrations in spring was higher than that in summer. The summer daytime high ozone is mainly due to favorable meteorological conditions
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while the spring nighttime high ozone could not be accurately explained in this study. Frequencies of the time in which the daily maximum ozone concentrations in 24h appeared show a two peaks type, one peak appeared in 1400–1500 hours during daytime and another appeared in 2300–0000 hours during nighttime. Analysis of the influences of meteorological parameters on daily averaged ozone indicates that ozone showed negative correlation with pressure as well as relative humidity and positive correlation with temperature, total solar radiation, sunshine duration, and wind speed during the study period. The significant impact factors for ozone daily variations were temperature, pressure, and total solar radiation. Further studies show that, solar radiation is a primary influence factor for the daytime variations of ozone concentrations at this site; transport of pollutants by wind could enhance the pollution at this site; precipitation has a significant role in the decrease of surface ozone. A multi-day ozone episode from 16 to 21 June 2003 was observed at this site. During the episode days, a typhoon names Soudelor moving along the eastern coast of China and passed by the eastern marine region of Jinan. Surface meteorological condition analysis and backward trajectory studies show that the episode is associated with the influence of typhoon Soudelor, attributing to both local photochemical processes and transport of air pollutants from southeastern coastal region, especially Yangtze River Delta region. Acknowledgements The authors would like to thank Ma Ruixian for her assistance in the word processing of the manuscript and Li Changmei for her help in the collection of the data. We gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model used in this publication. We also wish to thank the two reviewers for their helpful comments and suggestions on our manuscript.
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