It was a wet and windy Sunday morning which around 74000 runners left their homes in the early dawn to show the spirit of unity in Hong Kong, through the Standard Charted Marathon held on 17th Feb 2019. Clean Air Network requested 5 full marathon runners to help carry the Nitrogen dioxide (NO2) sensors with them to monitor the air along the running route.


NO2 sensor on runners


NO2 is a pollutant which can cause irritation of eyes, nose and throat, and when inhaled might cause lung irritations and decreased lung function. In areas with higher levels of nitrogen dioxide, a greater chance of asthma attacks and an increase in hospital stays because of respiratory complaints are observed. This means that some runners who had slight asthma or bronchial problems might get aggravated while running the marathon.

The Monitoring Results

The data collected by the runners showed that the NO2 levels throughout the marathon run showed around 100-200 μg/m3 at a 15-minute average concentration.

World Health Organization says according to the air quality guideline values that NO2 concentrations above 200 μg/m3 (1-hour mean) creates short term risks to the people. It also says that the mean concentration of NO2 should be kept as low as 40 μg/m3 annually for maintaining good health of the people.

The vehicles were diverted and roads closed for this period but also, the average concentration levels of NO2 we showing higher than expected. Do the marathon authorities need to invest more in cleaning the air quality along the roads for a longer period of time for the NO2 concentration to get diluted?

Air Quality References for Marathon racers

The runners might look at the air monitoring data from Environmental Protection Department (EPD) and say that it looks good but the sensors are kept around 60-80 meters above the ground on top of buildings whereas the runners run at a level of less than 2 meters on the ground. All of the runners said that they were feeling quite breathless while running inside the Western Tunnel. This breathlessness was due to the high amount of NO2 trapped in the tunnels which might not have been diluted.

Hong Kong EPD has around 16 monitoring stations in which 13 stations are general stations and 3 stations are roadside stations. There was a big difference between the actual NO2 data and the data showing on the EPD database.

Compare the monitoring data from runners and EPD stations

Clean Air Network would like to thank the 5 runners who volunteered to carry the sensor all the way throughout the race.


鯊魚 Kate Leung
熊貓 Chan Chun Fai
猛龍 Donald KWOK
極地 Alice Lee & 阿善
護士 Wong Wai Ping


The data monitored by the runners along the marathon route are shown below:

NO2 concentration and danger level

Route map of Hong Kong Marathon 2019 and the air monitoring location

Story posted on
22nd Feb, 2019


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