[Acute impact of combined exposure to cold spell and heavy pollution on circulatory disease mortality in the Beijing-Tianjin-Hebei Region and surrounding areas].

Objective

Investigating the impact of combined exposure to cold spells and heavy pollution on circulatory disease mortality in the population.

Methods

Daily population mortality, atmospheric fine particulate matter (PM2.5), and meteorological data were collected from 70 districts/counties in the Beijing-Tianjin-Hebei region and surrounding areas from 2013 to 2018. Cold spells were defined by daily mean temperature (<10th percentile) and duration (≥2 days), while heavy pollution events were defined by PM2.5 daily mean concentration (>75 μg/m³,>115 μg/m³,>150 μg/m³) and duration (≥2 days). Further, three overlapping combined exposure events were constructed. Based on this, three scenarios of combined exposure to cold spells and heavy pollution events were defined: Scenario A involved overlapping cold spell and heavy pollution periods; Scenario B featured a standalone heavy pollution event occurring within 7 days after a cold spell ended; Scenario C featured a standalone cold spell event occurring within 7 days after a heavy pollution event ended. A distributed lag nonlinear model was used to analyze the impact of each district/county's combined events on mortality risk. A meta-analysis was conducted to calculate cumulative relative risk (CRR) and attributable deaths. Subgroup analyses were also conducted.

Results

During the cold season (November to March) from 2013 to 2018, the mean daily temperatures and PM2.5 concentrations across all districts/counties were (3.1±5.8) ℃ and (98.58±78.19) μg/m³, respectively, with an average of (6±5) daily circulatory disease deaths. The CRR (95%CI) of combined exposure to cold spells and heavy pollution was 1.35 (1.14-1.60), higher than that of exposure to cold spells [1.14 (1.09-1.20)] or heavy pollution [1.08 (1.00-1.16)] alone. However, the exposure and lag-response relationships differed across various combined scenarios. At a cumulative lag of 21 days, the CRR values (95%CI) for circulatory disease mortality associated with combined scenarios A, B, and C were 1.24 (1.17-1.32), 1.12 (1.01-1.23), and 1.17 (1.11-1.22), respectively. Subgroup analysis revealed that the increased risk associated with combined events was primarily observed in specific disease subcategories such as ischemic heart disease and cerebrovascular disease.

Conclusion

Combined cold spells and heavy pollution exposure events increase the risk of multiple circulatory disease deaths in the population. Compared with other combined scenarios, higher risks may be associated when cold spells and heavy pollution overlap in time.