Background Epidemiological research on the effects of coarse particles (PM_c, particulate matter between 2.5 and 10 μm in aerodynamic diameter) on respiratory morbidity is sparse and inconclusive. Pneumonia is an inflammatory condition of lung caused by infections, which may be triggered and exacerbated by PM_c exposure.

Aim To estimate the effect of PM_c on emergency hospital admissions for pneumonia after controlling for PM_2.5 and gaseous pollutants.

Method PM_c concentrations were estimated by subtracting PM_2.5 from PM₁₀ measurements in each of the 10 air monitoring stations from January 2011 to December 2012 in Hong Kong and then citywide daily average concentrations of PM_c were computed from the 10 stations. Generalised additive Poisson models were used to examine the relationship between PM_c and daily emergency hospital admissions for pneumonia, adjusting for PM_2.5 and gaseous pollutants (NO₂, SO₂ and O₃). Subgroup analyses by gender and age were also performed to identify the most susceptible subpopulations.

Results PM_c and PM_2.5 were significantly associated with emergency pneumonia hospitalisations. Every 10 μg/m³ increment of PM_c in the past 4 days (lag₀–lag₃) was associated with a 3.33% (95% CI 1.54% to 5.15%) increase in emergency hospitalisations for pneumonia. The effect estimates of PM_c were robust to the adjustment of PM_2.5, NO₂ or SO₂, but attenuated on the inclusion of O₃ in the model. Women, children and older people might be more vulnerable to PM_c exposure.

Conclusions Short-term PM_c exposure is associated with emergency hospitalisations for pneumonia in Hong Kong. Air quality regulation specifically for PM_c might be considered.