Cold Climate Impact on Air-Pollution-Related Health Outcomes: A Scoping Review

Abstract

In cold temperatures, vehicles idle more, have high cold-start emissions including greenhouse gases, and have less effective exhaust filtration systems, which can cause up to ten-fold more harmful vehicular emissions. Only a few vehicle technologies have been tested for emissions below -7 °C (20 °F). Four-hundred-million people living in cities with sub-zero temperatures may be impacted. We conducted a scoping review to identify the existing knowledge about air-pollution-related health outcomes in a cold climate, and pinpoint any research gaps. Of 1019 papers identified, 76 were selected for review. The papers described short-term health impacts associated with air pollutants. However, most papers removed the possible direct effect of temperature on pollution and health by adjusting for temperature. Only eight papers formally explored the modifying effect of temperatures. Five studies identified how extreme cold and warm temperatures aggravated mortality/morbidity associated with ozone, particles, and carbon-monoxide. The other three found no health associations with tested pollutants and temperature. Additionally, in most papers, emissions could not be attributed solely to traffic. In conclusion, evidence on the relationship between cold temperatures, traffic-related pollution, and related health outcomes is lacking. Therefore, targeted research is required to guide vehicle regulations, assess extreme weather-related risks in the context of climate change, and inform public health interventions.

Keywords: climate change; cold climate; extreme weather; human health; low temperatures; traffic-related air pollution (TRAP); transportation; vehicle cold start; vehicle emissions.

Figure 1

PRISMA flow diagram.

Figure 2

Distribution of the various pollutants studied in relation to health outcomes. 1 CP = the number of papers which explored one type of criteria pollutant. 2 CP–6 CP = the number of papers that explored multiple combinations of 2–6 criteria pollutants. Other = pollutants explored other than criteria pollutants including: Black carbon, black smoke, NO, NOx, NO₃, SO₄, sulphate H2S PAHs, COH, trace elements (copper, zinc, bromine, lead, iron, silicon, calcium, manganese, nickel, vanadium, selenium, sulphur, and potassium), volatile organic compounds (VOCs) (formaldehyde, benzene, toluene, methyl tert-butyl ether (MTBE)), particles, PNC (particulate number concentration/UFP indicator) or UFP, Delta-C, PM_2.5–10, PN (particulate number), PNam (accumulation mode particle number), PM_2.5 bound hopanes, PMion (sum of sulphate nitrate and ammonium), PMrest (the difference between urban PM₁₀ and rural; a proxy for locally generated PM₁₀), PM_2.5 components, PM_<2.5, AMP (accumulation mode).

Figure 3

Pollution and health studies. Health outcomes with seasonal associations (A), the pollutants involved (B), and the temperature range reported (C). Legend: Blue = papers that used winter data only; yellow = papers that identified stronger associations with health outcomes in the warm seasons; gray = papers that identified strong associations with health outcomes in both warm and cold seasons; orange = papers that identified stronger associations with health outcomes in the cold season; blue = papers that did not identify seasonal associations with health outcomes; dark green = 0 °C to −7 °C; light green = below −7 °C.

Figure 3

Pollution and health studies. Health outcomes with seasonal associations (A), the pollutants involved (B), and the temperature range reported (C). Legend: Blue = papers that used winter data only; yellow = papers that identified stronger associations with health outcomes in the warm seasons; gray = papers that identified strong associations with health outcomes in both warm and cold seasons; orange = papers that identified stronger associations with health outcomes in the cold season; blue = papers that did not identify seasonal associations with health outcomes; dark green = 0 °C to −7 °C; light green = below −7 °C.

Figure 3

Pollution and health studies. Health outcomes with seasonal associations (A), the pollutants involved (B), and the temperature range reported (C). Legend: Blue = papers that used winter data only; yellow = papers that identified stronger associations with health outcomes in the warm seasons; gray = papers that identified strong associations with health outcomes in both warm and cold seasons; orange = papers that identified stronger associations with health outcomes in the cold season; blue = papers that did not identify seasonal associations with health outcomes; dark green = 0 °C to −7 °C; light green = below −7 °C.

Figure 4

Eight studies tested the temperature and air pollution with health outcomes. Blue arrow = association with tested pollutants black arrow = no association with tested pollutants (cardio = cardiovascular effects, RESP = respiratory disease); warm weather refers to temperatures between 23.3–40.6 °C.