A proposed population-health based metric for evaluating representativeness of air quality monitoring in cities: Using Hong Kong as a demonstration

Abstract

City air quality monitoring (AQM) network are typically sparsely distributed due to high operation costs. It is of the question of how well it can reflect public health risks to air pollution given the diversity and heterogeneity in pollution, and spatial variations in population density. Combing high-resolution air quality model, spatial population distribution and health risk factors, we proposed a population-health based metric for AQM representativeness. This metric was demonstrated in Hong Kong using hourly modelling data of PM10, PM2.5, NO2 and O3 in 2019 with grid cells of 45m * 48m. Individual and total hospital admission risks (%AR) of these pollutants were calculated for each cell, and compared with those calculated at 16 monitoring sites using the similarity frequency (SF) method. AQM Representativeness was evaluated by SF and a population-health based network representation index (PHNI), which is population-weighted SF over the study-domain. The representativeness varies substantially among sites as well as between population- and area-based evaluation methods, reflecting heterogeneity in pollution and population. The current AQM network reflects population health risks well for PM10 (PHNI = 0.87) and PM2.5 (PHNI = 0.82), but is less able to represent risks for NO2 (PHNI = 0.59) and O3 (PHNI = 0.78). Strong seasonal variability in PHNI was found for PM, increasing by >11% during autumn and winter compared to summer due to regional transport. NO2 is better represented in urban than rural, reflecting the heterogeneity of urban traffic pollution. Combined health risk (%ARtotal) is well represented by the current AQM network (PHNI = 1), which is more homogenous due to the dominance and anti-correlation of NO2 and O3 related %AR. The proposed PHNI metric is useful to compare the health risk representativeness of AQM for individual and multiple pollutants and can be used to compare the effectiveness of AQM across cities.

Fig 1. Population density and fixed site monitor (FSM) locations in Hong Kong’s districts, with FSM abbreviated as: Causeway Bay (CB), Central (CL), Central Western (CW).

Eastern (EN), Kwai Chung (KC), Kwun Tong (KT), Tap Mun (MB), Mong Kok (MK), Sham Shui Po (SP), Sha Tin (ST), Tung Chung (TC), Tseung Kwan O (TK), Tuen Mun (TM), Tai Po (TP), Tsuen Wan (TW), Yuen Long (YL). Outlines of Hong Kong’s districts reprinted from Esri China (Hong Kong) under a CC BY license, with permission from Esri China (Hong Kong), original copyright 2017.

Fig 2. Conversion from dynamic mesh of ADMS model output (points) to raster, with streets (dashed lines).

Fig 3. Representativeness of hospital admission risks (%AR) from fixed site monitor (FSM) network over Hong Kong based on annual and seasonal PM₁₀ concentrations in 2019.

Outlines of Hong Kong’s districts reprinted from Esri China (Hong Kong) under a CC BY license, with permission from Esri China (Hong Kong), original copyright 2017.

Fig 4. Representativeness of hospital admission risks (%AR) from fixed site monitor (FSM) network over Hong Kong based on annual and seasonal PM_2.5 concentrations in 2019.

Outlines of Hong Kong’s districts reprinted from Esri China (Hong Kong) under a CC BY license, with permission from Esri China (Hong Kong), original copyright 2017.

Fig 5. Representativeness of hospital admission risks (%AR) from fixed site monitor (FSM) network over Hong Kong based on annual and seasonal NO₂ concentrations in 2019.

Outlines of Hong Kong’s districts reprinted from Esri China (Hong Kong) under a CC BY license, with permission from Esri China (Hong Kong), original copyright 2017.

Fig 6. Representativeness of hospital admission risks (%AR) from fixed site monitor (FSM) network over Hong Kong based on annual and seasonal O₃ concentrations in 2019.

Outlines of Hong Kong’s districts reprinted from Esri China (Hong Kong) under a CC BY license, with permission from Esri China (Hong Kong), original copyright 2017.

Fig 7. Representativeness of total hospital admission risks (%AR total) from fixed site monitor (FSM) network over Hong Kong in 2019.

Outlines of Hong Kong’s districts reprinted from Esri China (Hong Kong) under a CC BY license, with permission from Esri China (Hong Kong), original copyright 2017.

Fig 8. Represented area and represented population (SF > 0.9) by fixed site monitor (FSM).

Fig 9. District-level population-based health representativeness for Hong Kong.

Outlines of Hong Kong’s districts reprinted from Esri China (Hong Kong) under a CC BY license, with permission from Esri China (Hong Kong), original copyright 2017.