New research from Blue Skies China shows the government’s proposed Air Quality Objectives (AQO) ammendments are considerably weaker than the current (2018) air pollution situation for fine respirable particles, or PM2.5.
The government’s new proposals, which will likely come into force in 2020, are based around the World Health Organization’s (WHO) Interim Target 2 (IT2):
- 25µg/m3 for annual PM2.5; and
- 50µg/m3 for 24-hour PM2.5.
The WHO also says governments may implement exceedances to help achieve the 24-hour targets. The Hong Kong government is proposing 35 exceedances for 24-hour PM2.5 (up from the current limit of 9), which means it can breach the target at any or all of the monitoring stations for 35 days each year. The government arrived at this figure through air quality modelling forecasts which suggested it would need at least 33 exceedances to comply with the IT2 target.
Targets are worse than today’s reality
There’s been much debate in the city on whether a lower target with exceedances is really better for public health. However, we haven’t seen any simple analysis to see how our air pollution situation today would fare with the proposed new PM2.5 targets. The table below shows the situation clearly: the actual 2018 air pollution situation is already within or better than the proposed targets: in other words, compliance with the newly proposed targets could mean more pollution in 2025 than we’ve seen in 2018.
|Actual 2018 situation||2025 government forecast||Proposed 2020-2025 target|
|24-hour PM2.5||50µg/m3 with 15 exceedances||50µg/m3 with 33 exceedances||50µg/m3 with 35 exceedances|
^average of all 13 monitoring stations: worst performing station 26µg/m3; second worst 22µg/m3; best 15µg/m3
Analysing the proposed Air Quality Objectives (AQOs) for PM2.5 using actual 2018 daily pollution data, we found the city would have exceeded the proposed daily 24-hour-PM2.5 target of 50µg/m3 on just 15 days in 2018. Although the government says its proposals are clearly a tightening of air pollution standards against 2012 pollution data (and we would agree with this), it is clearly a loosening of standards against Hong Kong’s actual 2018 pollution.
(The full-sized graph is available in the PDF report).
Meanwhile the proposed lowering of the annual PM2.5 target will make no difference to air quality, since, on average, Hong Kong is already within the IT2 annual target (25µg/m3) in 2018. All but one station (Tuen Mun) complied with the proposed annual target of 25µg/m3 (Tuen Mun’s average was 26µg/m3); the average result across the city was 19.8µg/m3, well within the average 25µg/m3 proposed by the new law. Again, the government claims the new target is a tightening simply because it is comparing against 2015, or 2012 data. Look at 2018 and the proposed IT2 annual PM2.5 target has already been met.
This is most interesting, not simply because it shows we are already within the WHO’s IT2, both annually and daily (with 15 exceedances); but because the annual target reduction is being used as the main reason to increase the number of daily exceedances from 9 to 35. For example, Professors Alexis Lau and Xiang-qian Lao claim we should accept 35 exceedances because of the general public health benefits in reducing the annual average; and that reducing the annual average should take priority over any increase in daily exceedances.
If Hong Kong annual PM2.5 was currently well above the WHO IT2 levels, then we would agree, lowering the annual average should take precedence over the 24-hour target, and if this meant more exceedances at the 24-hour level then so be it. However, it does not make any sense to make compromises on daily exceedances to reach a target we have already attained. Especially when those compromises indicate Hong Kong’s air pollution is forecast to get much worse in 2025.
A public consultation into the proposed AQOs will open in June: we encourage all interested parties to take part and ask tough questions of the government. Our research paper into the 24-hour PM2.5 data for 2018, and a brief discussion addressing the government’s recent defence of its proposals, can be downloaded here: HK-AQO-research.