Air quality changes after Hong Kong shipping emission policy: An accountability study

Background: On July 1st^, 2015, Hong Kong became the first city in Asia to implement a policy regulating sulfur dioxide (SO₂) in shipping emissions. We conducted an accountability study assessing the improvement in ambient air quality and estimating the effect on health outcomes of the policy.

Method: We used interrupted time series (ITS) with segmented regression to identify any change in ambient concentrations of SO₂ in contrast to other ambient pollutants (particulate matter <10 μm in diameter (PM₁₀), nitrogen dioxide (NO₂) and ozone (O₃)) at 10 monitoring stations in Hong Kong from 2010 to 2017. We validated these findings using cumulative sum control (CUSUM) charts. We used a validated risk assessment model to estimate effects of changes in air quality on death for natural causes, cardiovascular and respiratory diseases.

Results: Mean monthly concentrations of SO₂ fell abruptly at the monitoring station closest to the main shipping port (Kwai Chung (KC)) by -10.0 μgm³ p-value = 0.0004, but not elsewhere. No such changes were evident for the other pollutants (PM₁₀, NO₂, O₃). CUSUM charts confirmed a change in July 2015. Estimated deaths avoided per year as a result of the policy were 379, 72, 30 for all natural causes, respiratory and cardiovascular diseases respectively.

Conclusion: Implementation of the shipping emission policy in Hong Kong successfully reduced ambient SO₂, with the potential to reduce mortality. However, to gain full benefits, restrictions on shipping emissions need to be implemented throughout the region.