Project No: 16210023

Title: Unravelling contraption of particulate matter size and number distribution in urban microenvironments

Principal Investigator: Prof. Zhi NING


Urban air pollution has recently caught everyone’s attention whether it be from scientific community or public, due to the growing effects from the changing urban landscapes with the evolution of built environments. With the uprise in number of micro-built environments, the current knowledge about the transport and distribution of atmospheric pollutants, especially the particulate matter (PM), shall not sustain in the longer run. Hong Kong is known for the existence of many skyscrapers both in the magnitude of individual to dense buildings, and as such the relevance of understanding the PM size/number distribution becomes even significant, especially during air pollution episodes.

Thus, in the proposed study, we will develop and deploy a sensor-based PM size profiler, which will be capable of measuring PM number concentration in the size range of 0.3 to 10 µm. A maximum of 15 sensors will be employed to form a high-density sensor network spanning background site, individual buildings, and building clusters in Hong Kong. Each of these built environments will have sensors installed at three different heights to understand the PM size/number distribution with increase in height, and to determine the transport mechanism of the multi-size PM through the building clusters. Considering, the PM size and their transport will be impacted by everchanging meteorological conditions, this study will be carried out across four seasons, which will also allow us to determine the role of temperature and relative humidity on particle hygroscopicity with reference to change in height. For understanding the particle hygroscopicity, two sensor sets, with and without heating elements, will be deployed at any two building clusters/individual buildings depending on the relevant PM size distribution noted then.

From this proposal, we expect to encounter and address multiple scenarios of PM size/number distribution such as smaller PM size gradient with lower wind speeds but diversified PM number concentration, stagnation of multiple size PM in a building cluster, particle growth with changes in the seasons, and scattered/confiding PM number distribution in a building cluster, which will ultimately help in providing a cross-section view of PM size/number distribution across built environments with multiple characteristics, and this proposal shall be a stepping stone in alerting building management to regulate the building clusters as urban canopies. In addition, this study can provide an evidence-based approach, for policymakers and governments across the globe, in combating urban air pollution and provide mitigation measures to potential health implications amidst uprising micro-built environments.