NO2 Hotspots in Hong Kong 2019｜Greenpeace by 綠色和平東亞分部 Greenpeace East Asia

AIR POLLUTION:

NO2 Hotspots in Hong Kong 2019 Greenpeace Science Unit: Aidan FARROW Greenpeace East Asia: YEUNG Ling Chun and NG Hon Lam

Photo: Â© Greenpeace / Fung Pik Yee

報告概要背景 ●

本報告紀錄了綠色和平使用二氧化氮樣本收集器於灣仔、觀塘、深水埗、油尖旺、沙田(馬鞍山)等五區進行為期兩星期的二氧化氮監測的結果。各區均包含市民大眾容易接觸二氧化氮的地方，包括路邊的行人路、橫跨十字路口的行人天橋、小學、幼稚園及休憩公園。

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採樣在2019年7月進行。

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本調查及分析是為了找出本港二氧化氮污染黑點，以及確認是否可以研究城市中不同環境的二氧化氮濃度差異。透過研究同區不同地點污染物濃度的相對變化，可以讓公眾了解更多社區的空氣污染問題，並有效減少與有害空氣污染物的接觸。

調查方法 ●

本研究共安裝119支二氧化氮樣本收集器(包括26支空白樣本)，分佈於85個監測點，覆蓋7 類環境設定。

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調查包括20個「學校」樣本、13個「路邊」樣本、11個「行人天橋」樣本(和11個「路邊」樣本配對比較)、15個「公園」樣本、12個「空氣質素監測站」樣本(在鄰近4個空氣監測站的地點各裝上3支收集器)，和22個「自定採樣點」的樣本。

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所有樣本均由綠色和平支持者及義工協助設置。

主要結果 ●

是次監測比較了公園、學校及路邊的二氧化氮濃度。監測期間，於路邊錄得的二氧化氮濃度最高，不過變數也最大。一些學校錄得的濃度甚至高於路邊的平均濃度，然而大部分學校的數據仍較路邊理想。公園較為遠離陸路交通，其錄得的二氧化氮濃度亦最低 ,平均為 38.3 μg/m3。

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在學校樣本當中，以油尖旺區的2間學校(101.1μg/m3及 84.8μg/m3)和灣仔區1間學校(82.5 μg/m3)的二氧化氮濃度最高，而最低濃度的學校位於馬鞍山(34.3 μg/m3)。

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17個路邊監測點當中，只有1個錄得二氧化氮濃度低於40μg/m3；鯉魚門道接連東區海底隧道、與觀塘繞道交匯的監測站則錄得最高濃度(234.3 μg/m3)。

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設於行人天橋的樣本為繁忙道路和道路上空的空氣質素提供比較。結果皆顯示行人天橋的二氧化氮濃度低於路邊錄得的濃度，差距由6%至 46%不等，平均則低24%或18μg/m3。

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公園的監測結果清楚顯示位於巿區的公園錄得最高二氧化氮濃度，分別為油尖旺區(平均濃度56μg/m3)及深水埗區(平均濃度42 μg/m3)。

綠色和平觀點 ●

二氧化氮是威脅巿民健康的空氣污染物，研究指它與心血管、呼吸道疾病和肺癌等有關。香港高樓大廈密集，最令人關注的二氧化氮主要源頭是道路交通。是次調查結果反映市區的二氧化氮近乎避無可避。綠色和平促請政府限制私家車增長以舒緩交通擠塞情況、推動公共交通工具電動化及設立行人專用區，保護巿民健康。

Executive summary Background ●

This report describes the results of a 2-week of Nitrogen Dioxide (NO2) diffusion tube monitoring survey carried out in 5 districts in Hong Kong, namely Wan Chai, Kwun Tong, Sham Shui Po, Yau Tsim Mong, and Sha Tin (Ma On Shan). The 5 districts, where the public may be exposed to ambient NO2 on pedestrian routes by roadside, over footbridges, in schools and recreation parks, reach areas sensitive to the effects of air pollution.

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Monitoring was undertaken in July 2019.

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Methodology ●

119 diffusion tubes (including 26 blanks) were deployed across 85 monitoring locations covering a variety of environmental settings according to 7 categories.

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There are 20 ‘school’ samples, 13 ‘roadside’ samples, 11 ‘footbridge’ samples (paired with 11 roadside samples accordingly), 15 ‘park’ samples, 22 ‘flexible monitor’ samples, and 12 ‘AQMS co-location’ samples near 4 Air Quality Monitoring Stations (triplicate).

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All the samples were installed with the help of Greenpeace supporters and volunteers.

Key Findings ●

The measured NO2 concentrations at parks, schools, and roadside are compared in the monitoring survey. Monitors at roadside locations measured the highest concentrations of NO2 during the monitoring period but results were the most variable. Monitoring at some school locations measured NO2 concentrations higher than the average for roadside sites, though the majority of schools had cleaner air than that recorded at the roadside. Monitors located in parks, further away from road traffic sources, therefore measured the lowest concentrations of NO2, at an average of 38.3 μg/m3.

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The highest concentrations in the school category were recorded in Yau Tsim Mong District (101.1 μg/m3 and 84.8 μg/m3) and Wan Chai District (82.5 μg/m3), while the lowest concentrations were recorded in Ma On Shan (34.3 μg/m3).

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Among 17 roadside sampling sites, there is only 1 with the NO2 concentration below 40 μg/m3. The highest concentration was recorded at Lei Yue Mun Road (234.3 μg/m3), adjacent to the tunnel entrance which carries traffic on the Kwun Tong Bypass and to the Eastern Harbour Crossing.

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Diffusion tubes deployed on pedestrian footbridges provided a comparison of air quality at the height above the roadway. In all cases, the measured concentrations of NO2 at the footbridge level were lower than that recorded at the roadside by 6 to 46%, with an average NO2 reduction of 24% or 18 μg/m3.

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The results of diffusion tube monitoring in parks show a clear pattern with the highest NO2 concentrations recorded in the down-town districts of Yau Tsim Mong (average concentration 56μg/m3) and Sham Shui Po (average concentration 42 μg/m3).

Greenpeace's view ●

NO2 is an air pollutant that threatens citizen health, as it is reported to associate with cardiovascular, respiratory diseases, and lung cancer. Road transportation emission is the major source that concerns us the most in Hong Kong, the high-density, high-rise city. It is reflected in the current survey that there is almost no way to escape from the pollutant in urban areas. Greenpeace calls on the Government to decrease traffic density by restraining the growth of private cars, promote the use of electric vehicles in public transport, and set up pedestrian zones, so as to protect the public’s health.

NO2 Air Quality Monitoring in Hong Kong, August 2019 Contents Introduction Policy Context Materials and Methods

5 5 6

Study Area

Diffusion Tube

AQMS Co-location

School

Roadside

Footbridge

Park

Flexible Monitor

Travel Blank

Existing Monitoring Data Results and Discussion Diffusion Tube Monitoring Results

9 10 10

School

Roadside

Footbridge

Park

Comparison of Park, School and at Roadside Location

Flexible Monitor

AQMS Analysis

Conclusions

Glossary

Appendix 1: Bias Adjustment

1 Introduction 1.1

This report describes the results of a 2-week of Nitrogen Dioxide (NO2) diffusion tube monitoring survey carried out in 5 districts in Hong Kong, namely Wan Chai, Kwun Tong, Sham Shui Po, Yau Tsim Mong, and Sha Tin (Ma On Shan). Monitoring undertaken in July 2019 included sites near schools, parks, footbridges, roadside and Air Quality Monitoring Stations (AQMSs) in the above districts.

1.2

The survey and analysis has been designed to identify NO2 hotspots in Hong Kong, and to determine if different levels of NO2 can be detected in diverse environmental settings within the city. Determining relative changes in concentration between parks, school bridges and roadside can help inform the public to reduce exposure to harmful pollutants. The survey was limited in scope by the short 2-week duration of sampling. It is acknowledged that the short-term data reflects only the air quality during the sampling period. Necessarily the results are considered indicative of air quality conditions at the sampling locations and no direct comparison can be made with long-term conditions, such as annual means for example.

1.3

To complement the short-term diffusion tube survey, further analysis has been carried out using long-term data obtained from the Air Quality Monitoring Network of Hong Kong.

Policy Context 1.4

The Environmental Protection Department of the Hong Kong Special Administrative Region is responsible for air quality in the city. They published Air Quality Objectives (AQOs) according to the Air Pollution Control Ordinance (Cap. 311). The AQOs for NO2 are aligned with the World Health Organization’s Air Quality Guidelines (AQGs) set out in Table 11.

Table 1:

Pollutant

NO2

World Health Organisation Guidelines and Hong Kong Air Quality Objectives for NO2

Averaging Time

World Health Organisation Guideline (μg/m3)

Hong Kong Air Quality Objective (μg/m3)

Hong Kong Number of Exceedances allowed

1 hour

200

Annual

Hong Kong Environmental Protection Department. (2013). Hong Kong’s Air Quality Objectives. Retrieved from http://www.epd.gov.hk/epd/english/environmentinhk/air/air_quality_objectives/air_quality_objectives.htm l

2 Materials and Methods Study Area 2.1

Hong Kong is a coastal city which borders Guangdong province in southern China and the South China Sea. Located at the mouth of the Pearl River Delta, it is a major port and incorporates numerous islands and peninsulas.

2.2

The study took place in the District of Wan Chai, Kwun Tong, Sham Shui Po, Yau Tsim Mong, and Sha Tin (Ma On Shan) and monitors were distributed in locations shown in Figure 1. The 5 districts, where the public may be exposed to ambient NO2 on pedestrian routes by roadside, over footbridges at road crossings, in schools and kindergartens, and recreation parks, reach areas sensitive to the effects of air pollution.

2.3

Data from the 2017 Environmental Protection Department Emission Inventory2 is shown in Figure 2. The principal source of Nitrogen Oxides (NOx) in Hong Kong during the year was marine navigation (37%), followed by public electricity generation (27%), and road transport (20%). Approximately 70% of NO2 in Hong Kong is produced locally3, with the remainder being transported from neighbouring regions.

Figure 1: The Study Area and Monitoring Locations including AQMS sites (Red), Parks (Orange), Footbridges (Yellow), Flexible Monitors (Green), Roadside (Purple) and Schools (Blue) Background map by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL. 2

Hong Kong Environmental Protection Department. (2017). Hong Kong Air Pollutant Emission Inventory Nitrogen Oxides. Retrieved September2, 2019, from https://www.epd.gov.hk/epd/english/environmentinhk/air/data/emission_inve_nox_C.html

Yim, S. H. L., Hou, X., Guo, J., & Yang, Y. (2019). Contribution of local emissions and transboundary air pollution to air quality in Hong Kong during El Niño-Southern Oscillation and heatwaves. Atmospheric Research, 218(October 2018), 50–58. https://doi.org/10.1016/j.atmosres.2018.10.021

Figure 2: 2017 NOx emission sources (Environmental Protection Department)

Diffusion Tube 2.4

Monitoring for NO2 was undertaken by Greenpeace between 11 July 2019 and 30 July 2019 using diffusion tubes prepared and analysed by Gradko Ltd (UK). 119 diffusion tubes were installed across monitoring locations covering a variety of environmental settings according to 7 categories. These categories are ‘School’, ‘Roadside’, ‘Footbridge’, ‘Park’, ‘Flexible Monitor’, ‘Travel Blank’ and ‘AQMS Co-location’. Each category is described and summarised in Table 2. Details of each monitor location are provided in Table 3 and Figure 3.

2.5

During the monitoring period political unrest in Hong Kong led to street closures and alternative roads relating to pollutant emissions. However, the duration of protests affecting any individual monitoring location was less than 6 hours, within the total monitoring time of approximate 300 hours at each site. We therefore consider the potential for protests to have made a significant impact on the results to be minimal.

AQMS Co-location 2.6

Diffusion tube monitors were installed at sites adjacent to the official Air Quality Monitoring Stations (AQMSs) at Causeway Bay and Mong Kok. Additionally, diffusion tubes were installed at the roadside, below the roof-top AQMS monitoring sites at Kwun Tong and Sham Shui Po. At each location 4 individual diffusion tubes, the triplicate of active tubes as well as a blank one remained unexposed to the atmosphere, were installed.

2.7

Bias in diffusion tube monitoring results can be corrected by comparing results with a reference method analyser. This reduced the uncertainty in the results of the survey. The results of triplicate tubes from Causeway Bay and Mong Kok were used to make this comparison. An adjustment factor was calculated based on each comparison and applied to the results of the monitors in other categories. Full process is detailed in Appendix 1.

School 2.8

Monitoring was undertaken at 20 primary schools and kindergartens, 4 in each district. In each case a diffusion tube monitor was installed with a blank one remained sealed. The blank was considered as a means of accounting for measurement bias and full details are provided in Appendix 1. Locations in each school were chosen to improve the inter-comparability of the results. Monitors were installed at 2.5-meter (maximum 3.1 meters, minimum 2.3 meters) height above the ground where possible and the distance to the nearest major road was recorded. All schools selected are within 20 meters of a major road in the district.

Roadside 2.9

Monitoring was undertaken at 17 roadside locations, in which 4 were also ‘AQMS Co-location’ sites where the monitors were installed adjacent to an official Hong Kong Air Quality Monitoring Station (AQMS). Among the 17 roadside monitors, 11 of them also served as roadside counterparts of the footbridge monitors (details in section 2.10). Monitoring height and distance from the road were recorded to improve the inter-comparability of the results. All monitors were between 2.3 -2.8 meters high.

Footbridge 2.10

Eleven of diffusion tubes were installed on the elevated walkways on footbridges over major roads and they were in pair of another 11 diffusion tubes on the roadside beneath the footbridges. Pairs of footbridge and roadside monitors have been designed for the direct comparison between street-level and bridge-level measurements of NO2.

Park 2.11

Monitoring was undertaken at 15 parks and leisure areas set back from roadside pollution sources. 3 parks were chosen in each district. A subset of these sites were background sites, away from major roads. Its pollution levels are more representative of the neighbourhood than a specific location on an individual street. Monitoring height and distance from the road were recorded to improve the inter-comparability of the results. All monitors were between 2.3 - 3 meters high.

Flexible Monitor 2.12

Twenty-two flexible monitors were installed by Greenpeace supporters in locations of their choice. These monitors have wide spatial coverage despite their primary purpose was to provide specific information of sites. However, flexible monitors were not at comparable heights or locations with respect to other tubes in the survey. This limits the direct comparisons with monitors installed in other locations, so that results are presented for all locations, while only tubes set at less than 3 meters in elevation are included in the analysis. Diffusion tubes installed on tall buildings are discounted from any comparative analysis so that only ground level conditions are counted.

Travel Blank 2.13

Two travel blank tubes were used throughout the survey. They were transported to and from the analytical laboratory with the other monitors. The 2 tubes were stored in a cool dry location during monitoring and were carried to the monitoring locations in installation and collection. NO2 levels measured by the travel blank were subtracted from the results recorded by other monitors accounting for systematic bias resulting from exposure to NO2 during transport. Table 2:

Summary of Diffusion Tube Monitors

Monitor Category

Number of Monitors

Number of Blanks

School

20 diffusion tubes

Roadside

13 diffusion tubes (4 further roadside locations are AQMS 1, 2 ,3 & 4)

Footbridge

11 diffusion tubes

Park

15 diffusion tubes

Flexible Monitor

22 diffusion tubes

Travel Blank

2 diffusion tubes

AQMS

12 diffusion tubes at 4 roadside locations are located near AQMS sites

4 diffusion tubes

Existing Monitoring Data 2.14

There are 16 static Air Quality Monitoring Stations (AQMSs) in Hong Kong operated by the Environmental Protection Department. These 16 stations cover 18 districts. Many of them are at roof height and only 3 out of 16 are roadside stations set up at pedestrian level.

2.15

Annual mean data from the AQMSs has been collated4.

Air Science Group, & Hong Kong Environmental Protection Department. (2019). Air Quality in Hong Kong 2018 Statistical Summary. Retrieved from http://www.aqhi.gov.hk/api_history/english/report/files/2018StatSum_enFinal.pdf

3 Results and Discussion Diffusion Tube Monitoring Results 3.1

Results of the diffusion tube monitoring survey are summarised in Table 3. Each tube was exposed for a short sampling time of only 2 weeks. The results, therefore, represent air quality conditions in the period only. The NO2 concentrations reported here are indicative of air quality in the monitoring locations and allow intercomparison between sites. However, it is not possible to estimate the annual mean of NO2 concentrations using this short-term data because air quality conditions are very sensitive to changes in weather and emission characteristics.

3.2

Results reveal wide variation in NO2 concentrations across Hong Kong with the highest value 234.3μg/m3 recorded at roadside location in Kwun Tong. The lowest value 18.5 μg/m3, measured by a flexible monitor in a suburban garden, was recorded in Yuen Long. Table 3:

Diffusion Tube Locations and Bias Adjusted Results

Category

District

Bias Adjusted NO2 (μg/m3)

AQMS 1 Causeway Bay

Wan Chai

AQMS 2 Mong Kok AQMS 3 Kwun Tong

Latitude Longitude

Height

95.1*

22.2800

114.1853

2.50m

Yau Tsim Mong

76.4*

22.3226

114.1684

2.65m

Kwun Tong

112.1*

22.3132

114.2248

2.30m

Sham Shui Po

75.4*

22.3298

114.1592

2.50m

Park 1

Wan Chai

23.1

22.2742

114.1886

2.30m

Park 2

Wan Chai

30.9

22.2700

114.1843

2.60m

Park 3

Wan Chai

29.5

22.2803

114.1916

2.50m

Park 4

Yau Tsim Mong

52.2

22.3159

114.1662

2.50m

Park 5

Yau Tsim Mong

62.2

22.3174

114.1721

2.50m

Park 6

Yau Tsim Mong

53.7

22.2965

114.1772

2.34m

Park 7

Kwun Tong

26.0

22.3248

114.2193

2.50m

Park 8

Kwun Tong

37.7

22.3148

114.2265

2.60m

Park 9

Kwun Tong

45.4

22.3132

114.2166

3.00m

Park 10

Sham Shui Po

45.0

22.3386

114.1422

3.00m

Park 11

Sham Shui Po

40.6

22.3262

114.1592

2.80m

Park 12

Sham Shui Po

40.5

22.3372

114.1510

2.50m

Park 13

Sha Tin (Ma On Shan)

31.4

22.4136

114.2221

2.60m

Park 14

Sha Tin (Ma On Shan)

33.0

22.4185

114.2274

2.50m

Park 15

Sha Tin (Ma On Shan)

23.3

22.4280

114.2301

2.50m

Wan Chai

48.7

22.2779

114.1679

10.40m

AQMS 4 Sham Shui Po

Footbridge 1

Roadside 1

Wan Chai

67.2

22.2779

114.1681

2.50m

Footbridge 2

Wan Chai

45.5

22.2781

114.1732

7.00m

Roadside 2

Wan Chai

66.8

22.2781

114.1731

2.50m

Footbridge 3

Wan Chai

54.9

22.2796

114.1862

8.40m

Footbridge 4

Yau Tsim Mong

53.9

22.3124

114.1675

8.33m

Roadside 4

Yau Tsim Mong

73.9

22.3126

114.1684

2.37m

Footbridge 5

Yau Tsim Mong

78.4

22.3212

114.1713

7.53m

Roadside 5

Yau Tsim Mong

88.1

22.3213

114.1712

2.34m

Footbridge 6

Kwun Tong

90.2

22.3132

114.2242

8.30m

Footbridge 7

Kwun Tong

78.1

22.3107

114.2286

7.70m

Roadside 7

Kwun Tong

83.6

22.3108

114.2287

2.90m

Footbridge 8

Sham Shui Po

60.4

22.3328

114.1665

8.10m

Roadside 8

Sham Shui Po

71.1

22.3328

114.1665

2.50m

Footbridge 9

Sham Shui Po

53.5

22.3305

114.1598

8.80m

Footbridge 10

Sha Tin (Ma On Shan)

32.6

22.4208

114.2269

10.00m

Roadside 10

Sha Tin (Ma On Shan)

60.4

22.4223

114.2275

2.50m

Footbridge 11

Sha Tin (Ma On Shan)

32.2

22.4259

114.2312

10.30m

Roadside 11

Sha Tin (Ma On Shan)

35.7

22.4260

114.2315

2.30m

Roadside 12

Yau Tsim Mong

66.1

22.3027

114.1717

2.75m

Roadside 13

Kwun Tong

74.9

22.3108

114.2251

2.80m

Roadside 14

Kwun Tong

234.3

22.3058

114.2344

2.50m

Roadside 15

Kwun Tong

60.7

22.3203

114.2090

2.50m

Roadside 16

Sham Shui Po

63.7

22.3316

114.1609

2.50m

School 1

Wan Chai

83.9

22.2778

114.1754

2.50m

School 2

Wan Chai

37.0

22.2751

114.1767

2.30m

School 3

Wan Chai

46.8

22.2832

114.1912

2.50m

School 4

Wan Chai

42.5

22.2790

114.1872

2.50m

School 5

Yau Tsim Mong

57.5

22.3225

114.1655

2.56m

School 6

Yau Tsim Mong

101.1

22.3076

114.1728

2.75m

School 7

Yau Tsim Mong

84.8

22.3012

114.1682

2.40m

School 8

Yau Tsim Mong

62.8

22.3140

114.1711

2.50m

School 9

Kwun Tong

59.2

22.3343

114.2105

2.70m

School 10

Kwun Tong

70.4

22.3287

114.2120

2.50m

School 11

Kwun Tong

46.3

22.3164

114.2176

2.70m

School 12

Kwun Tong

55.2

22.3152

114.2231

2.50m

School 13

Sham Shui Po

55.8

22.3367

114.1544

2.50m

School 14

Sham Shui Po

44.7

22.3271

114.1653

2.50m

School 15

Sham Shui Po

58.0

22.3348

114.1576

3.10m

School 16

Sham Shui Po

48.8

22.3341

114.1537

2.70m

School 17

Sha Tin (Ma On Shan)

43.3

22.4071

114.2195

2.50m

School 18

Sha Tin (Ma On Shan)

34.3

22.4171

114.2310

2.50m

School 19

Sha Tin (Ma On Shan)

36.4

22.4245

114.2337

2.65m

School 20

Sha Tin (Ma On Shan)

52.2

22.4062

114.2227

2.64m

Flexible Tube 1

Yuen Long

18.5

22.4894

114.0510

1.00m

Flexible Tube 2

Wong Tai Sin

34.2

22.3379

114.1952 12th Floor

Flexible Tube 3

Kwun Tong

26.2

22.3080

114.2358 36th Floor

Flexible Tube 4

Wong Tai Sin

33.3

22.3423

114.2013 4th Floor

Flexible Tube 5

Kowloon City

31.0

22.3189

114.1778 2nd Floor

Flexible Tube 6

Kwai Tsing

33.8

22.3466

114.1100 17th Floor

Flexible Tube 7

Sha Tin

32.0

22.3864

114.2027 17th Floor

Flexible Tube 8

Tsuen Wan

43.7

22.3797

114.1287

2.00m

Flexible Tube 9

Wan Chai

57.8

22.2772

114.1689

2.00m

Flexible Tube 10

Central and Western

23.8

22.2852

114.1352 4th Floor

Flexible Tube 11

Tsuen Wan

30.8

22.3531

114.0605 19th Floor

Flexible Tube 12

Sha Tin

29.0

22.3791

114.1745 23th Floor

Flexible Tube 13

Kwun Tong

31.2

22.3091

114.2261 11th Floor

Flexible Tube 14

Sai Kung

26.7

22.3071

114.2626 39th Floor

Flexible Tube 15

Tuen Mun

38.4

22.3821

113.9715 19th Floor

Flexible Tube 16

Yau Tsim Mong

49.5

22.3026

114.1724

Flexible Tube 17

Yuen Long

29.0

22.4717

113.9999 15th Floor

Flexible Tube 18

Sha Tin

22.0

22.4209

114.2251 28th Floor

Flexible Tube 19

Tai Po

24.3

22.4465

114.1673 11th Floor

Flexible Tube 20

Southern

25.5

22.2508

114.1398 32th Floor

Flexible Tube 21

Yau Tsim Mong

38.3

22.3236

114.1624 8th Floor

Flexible Tube 22

Wong Tai Sin

79.0

22.3339

114.1982

2.00m

2.75m

*Mean of triplicate diffusion tubes

School 3.3

Monitoring was undertaken at 20 primary schools and kindergartens, 4 in each district. The results are presented in Table 3 and Figure 3. The highest concentrations were recorded in Yau Tsim Mong and Wan Chai District while the lowest were recorded in the north-eastern part of Shatin District (Ma On Shan).

Figure 3: NO2 Diffusion Tube Results (μg/m3) at Schools in Hong Kong Background map by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.

Roadside 3.4

Monitoring results at roadside sites has the highest concentrations of the whole monitoring survey. These results are shown in Figure 4 and Table 3. The highest concentration was recorded at Lei Yue Mun Road (Kwun Tong District), adjacent to the tunnel entrance which carries traffic on the Kwun Tong Bypass and to the Eastern Harbour Crossing Approach. It is likely that traffic emissions released at the tunnel entrance have contributed to this measurement.

Figure 4: NO2 Diffusion Tube Results (μg/m3) at Roadside sites in Hong Kong Background map by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.

Footbridge 3.5

Diffusion tubes installed on pedestrian footbridges provided a comparison of air quality at height above the roadway. The results of diffusion tube measurements at roadside and footbridges are presented in Figures 5 and 6 as well as in Table 3.

3.6

In all cases the measured concentrations of NO2 at footbridge was lower than that recorded at the roadside. Differences in the measured NO2 concentrations ranged from 6 to 46% with an average NO2 reduction of 24% or 18 μg/m3. Monitoring heights varied according to the height of the footbridge and ranged between 7 and 10 meters. The greatest reduction in NO2 corresponds to Footbridge 3, where monitoring was undertaken 8.4 meters above the road.

Figure 5: NO2 Diffusion Tube Results at Footbridges and Roadside sites in Hong Kong (μg/m3). Only roadside locations with a corresponding footbridge are shown. Background map by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.

Figure 6: The difference between 2-week average NO2 Diffusion Tube results at Footbridges and Roadside sites in Hong Kong (μg/m3)

Park 3.7

The results of diffusion tube monitoring in parks across Hong Kong are shown in Figure 7 and Table 3. Monitoring results show a clear pattern with the highest NO2 concentrations recorded at parks in the down-town Districts of Yau Tsim Mong and Sham Shui Po.

Figure 7: NO2 Diffusion Tube Results at Parks in Hong Kong (μg/m3) Background map by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.

Comparison of Park, School and at Roadside Location 3.8

The measured NO2 concentrations in parks, at schools and at roadside locations are compared in Figure 8. Monitors at roadside locations measured the highest concentrations of NO2 during the period but the results are also the most variable. Monitoring at some school locations measured NO2 concentrations higher than the average for roadside, thought the majority of schools has cleaner air than that recorded at the roadside. Monitors located in parks, further away from road traffic sources, therefore measured the lowest concentrations of NO2. These comparisons are true in all districts of Hong Kong where monitoring was undertaken except Yau Tsim Mong. In most locations, roadside sites measured the highest level of NO2, followed by school sites and finally parks. However, in Yau Tsim Mong, the measured concentrations at roadside and school site are comparable (Figure 9).

Figure 8: Maximum, upper quartile, lower quartile and minimum 2-week NO2 Diffusion Tube measurements at Parks, Roadside locations and Schools in Hong Kong (μg/m3)

Figure 9: 2-week NO2 Diffusion Tube measurements at districts in Hong Kong. The average of all monitoring sites is presented with subsets showing roadside sites, schools and parks (μg/m3)

Flexible Monitor 3.9

Greenpeace supporters installed diffusion tubes in locations of their choosing. The results of these tubes are presented in Figure 10 and should be interpreted with reference to Table 3 where the approximate height of the diffusion tube monitor above ground was provided.

Figure 10: NO2 Diffusion Tube Results (μg/m3) at locations selected by Greenpeace supporters. Results reflect the height and location of the monitor, see Table 3 for monitoring height. Background map by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.

AQMS Analysis 3.10

Air Quality data provided by the Air Quality in Hong Kong 2018 Statistical Summary5 shows that the annual average AQO for NO2 of 40 μg/m3 was exceeded at 9 out of 16 AQMSs (Table 4). The annual mean concentration at the 3 roadside Air Quality Monitoring Stations in Causeway Bay, Central, and Mong Kok were approximately double the objective.

Table 4:

Station

2018 Annual Mean NO2 concentrations at monitoring stations in Hong Kong6

2018 Annual Mean 3 ) NO2 (μg/m

Station

2018 Annual Mean 3 ) NO2 (μg/m

Central/Western

Tuen Mun

Eastern

Tung Chung

Kwun Tong

Tai Po

Sham Shui Po

Sha Tin

Kwai Chung

Tap Mun

Tsuen Wan

Causeway Bay

Tseung Kwan O

Central

Yuen Long

Mong Kok

4 Conclusions 4.1

A 2-week NO2 diffusion tube survey was undertaken at locations across Hong Kong during July 2019. Results of the diffusion tube monitoring found significant spatial variability in the city. The results of the short term monitoring survey provide indicative evidence of air quality conditions across the city. They cannot be readily compared to annual mean objectives set by Hong Kong’s Environmental Protection Department.

4.2

Diffusion tubes were installed to test the relative difference in air quality conditions at roadside sites, on footbridges over major roads, in parks, at schools and locations selected by Greenpeace supporters. The highest concentrations were recorded at roadside locations, while monitors in parks measured the lowest levels of NO2.

4.3

Results of the comparison between roadside monitors and those stations on footbridges found that in all cases NO2 concentrations were lower on the elevated bridge. This suggests

that pedestrians can reduce their exposure to NO2 by choosing to use elevated crossings rather than crossings at street level. 4.4

Analysis shows that the air in parks is cleanest in terms of NO2 in these ‘background’ sites away from road traffic. By mapping the NO2 concentrations recorded in the parks we have shown that the down-town Districts of Yau Tsmin Mong and Sham Shui Po have higher concentrations than those on the city’s edges.

4.5

Data recorded by AQMSs in Hong Kong in 2018 showed that the annual average AQO for NO2 of 40 μg/m3 was exceeded at 9 out of 16 AQMS.

5 Glossary AQMS

Air Quality Monitoring Station

NO2

Nitrogen dioxide

NOx

Mono-Nitrogen oxides

μg/m3

Microgrammes per cubic meter

WHO

World Health Organisation

AQO

Air Quality Objectives

Appendix 1: Bias Adjustment The NO2 diffusion tube monitors used in the co-location study were installed between 13 July 2019 and 27 July 2019. The Co-locations of diffusion tubes with automatic monitors allow results to be corrected for bias. Data from triplicate diffusion tubes co-located with AQMS-1 and AQMS-2 in Causeway Bay and Mong Kok respectively have been compared to the concentrations recorded by each AQMS site. Ratified data was not available at the time of analysis and so the unratified results from AQMS monitoring, having been retrieved from the Hong Kong Government data website7, were used. All diffusion tube data were first blank subtracted, with location specific blanks at each school, travel blank and laboratory blank being removed. A bias adjustment factor was then calculated and applied to all diffusion tube sites. The factor and the data used to derive it are shown in Table A1. Table A1: Derivation of Bias Adjustment Factors

Station

AQMS-1

AQMS-2

A. Automatic Monitor Period Mean (μg/m3)

82.6

83.7

Diffusion tube 1 Result (μg/m3)

154.3

117.6

Diffusion tube 2 Result (μg/m3)

144.0

121.9

Diffusion tube 3 Result (μg/m3)

148.3

119.1

Blank

1.8

1.5

Lab Blank

0.1

Travel Blank 1

0.5

Travel Blank 2

0.8

Travel Blank Average

0.7

B. Average of Triplicate Diffusion Tube Measurements (μg/m3)

146.3

117.3

A/B

0.56

0.71

Bias Adjustment Factor Applied

0.639

Unique bias adjustment factors determined at each school monitoring site were calculated using the results of the blank monitor installed at each school. At each school monitoring site a separate blank diffusion tube was installed. The results of each diffusion tube were used to calculate a unique bias adjustment factor for each school following the

Hong Kong Environmental Protection Department. (n.d.). Past 24-hour Pollutant Concentration of individual Air Quality Monitoring Stations. Retrieved September2, 2019, from https://data.gov.hk/tc-data/dataset/hk-epd-airteam-past24hr-pc-of-individual-air-quality-monitoring-stations

method outlined above. Results of the blank diffusion tubes at each school and the bias adjustment factor calculated are shown in Table A2. Table A2: School Monitor Blank Results and Bias Adjustment Factors

School

Blank (μg/m )

Bias Adjustment Factor

School 1

1.5

0.639

School 11

1.1

0.637

School 2

1.2

0.637

School 12

1.8

0.640

School 3

1.6

0.639

School 13

1.5

0.639

School 4

1.0

0.636

School 14

1.1

0.637

School 5

1.2

0.637

School 15

1.6

0.639

School 6

1.8

0.640

School 16

1.2

0.637

School 7

1.2

0.637

School 17

1.3

0.637

School 8

1.4

0.638

School 18

1.4

0.638

School 9

1.6

0.639

School 19

1.3

0.638

School 10

1.7

0.640

School 20

1.2

0.637

School

Blank (μg/m )

Bias Adjustment Factor

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