Clean Air Network (CAN) has been collaborating with the Institute for the Environment of the Hong Kong University of Science and Technology (IENV HKUST) in a 2-year project “Clean Air Schools for Hong Kong” to conduct a comprehensive indoor and outdoor air quality measurement in Hong Kong. Considering the general public spends most of their time indoors, especially in schools and offices, measurement of indoor air quality is essential to understand the profound impact of air pollutants such as fine suspended particles (PM2.5), respirable suspended particles (PM10), carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3) and carbon dioxide (CO2).
Thus, the IENV and the CAN co-organized the first school-based air quality monitoring network in Hong Kong, currently focusing on densely populated areas next to heavily trafficked roads across two districts, namely Sham Shui Po and Tuen Mun. Though Hong Kong has one regulatory air quality monitoring station in both districts, maintained by Environment Protection Department, which provides regional air quality information. However, it lacks pollutant dynamics at the microenvironment level.
These air quality monitors were installed in four schools in each of the two districts, to understand Hong Kong’s air pollution characteristics and the distribution pattern of air pollutants indoors and outdoors in urban areas. The data collected were converted into Air Quality Health Index (AQHI) for easier understanding. The data thus obtained shall provide mitigation measures to improve indoor air quality and ultimately improve the living environment for the public in Hong Kong.
Figure 1: Air Quality Health Index scale (adopted from EPD) [1]The schools have been classified per 3 criteria which are named periphery, community, and highway vicinity. Since the school-based air quality monitoring has begun in August 2022, the project could extract data for the 1st quarter of the monitoring period (August 2022 to October 2022) and generate an analysis of the air quality for the schools.
Figure 2: Locations of participating schools
Outdoor air quality and Air Quality Health Index (AQHI) for schools
Some of the insights generated were:
The AQHI in the periphery of the district where there is less traffic and more greenery, did not necessarily have better air quality than the heart of the district where there are high traffic roads.
Within schools located in the community, the schools with close proximity to main roads or higher traffic roads had a higher AQHI than schools far away from main roads or high traffic roads.
Interestingly, schools located near highways generally had a better AQHI. On one hand, the schools lying in the periphery had the highest occurrences of bad air quality represented by AQHI greater than or equal to 7 (AQHI≥7) compared to the schools in the community or highway. On the other hand, AQHI ≤ 3 representing good air quality was the highest among the highways compared to the periphery or community. This might have been due to the interconnected relationship between nitrogen monoxide (NO) , a primary pollutant and O3 a secondary pollutant. Highway sites with high traffic flow produce appreciable NO which is convertible into O3. With a higher weighting factor of O3 in AQHI calculation, a relatively lower O3 concentration in the highway sites results in better AQHI in the highway site compared to community and periphery site.
Figure 3: Formation of secondary pollutant Ozone from vehicle emissionsFigure 4: Percentage of hours of the total measured hours
Indoor Air Quality (IAQ) for schools
Some of the insights generated were:
The Indoor Air Quality (IAQ) during the summer holiday period in August 2022 was excellent but after the schools started their new academic year in September 2022, the IAQ dropped. The IAQ deterioration in September 2022 was due to insufficient ventilation during the air-conditioned operation period, as well as additional pollution episodes outside. The situation started to improve in October 2022 due to the opening of windows as the weather turned cooler.
One of the participating schools had very poor IAQ in August due to an air disinfector that they were using which in turn generated high PM2.5 levels in the classroom. After the school was informed, relevant actions were taken and the IAQ levels improved.
The IAQ was occasionally at the worst level even though the outdoor air quality was at an acceptable level (AQHI ≤ 6). This was due to the building up of CO2 concentration in classrooms because of insufficient ventilation.
Unavoidable infiltration of outdoor pollutants into the classroom could lead to unsatisfactory IAQ during unoccupied periods when the outdoor air quality levels were poor (AQHI ≥ 8).
Share page
