This review examines the epidemiological evidence linking long-term exposure to ambient air pollution, particularly fine particulate matter (PM₂.₅), with mortality from all causes, cardiovascular disease, and respiratory disease. The authors conducted a meta-analysis of studies published up to January 2013, focusing on the effects of PM₂.₅, nitrogen dioxide (NO₂), and elemental carbon (EC). Key findings include: 1. **Mortality from All Causes**: A significant increase in mortality risk was observed with each 10 μg/m³ increase in PM₂.₅ exposure, with a pooled estimate of 6% (95% CI 4-8%) for all-cause mortality and 11% (95% CI 5-16%) for cardiovascular mortality. 2. **Mortality from Cardiovascular Disease**: Long-term exposure to PM₂.₅ was more strongly associated with cardiovascular mortality, particularly ischemic heart disease, compared to non-malignant respiratory diseases. The pooled estimate for cardiovascular mortality was 3% (95% CI -6, 13%). 3. **Heterogeneity in Effect Estimates**: Significant heterogeneity was found across studies, likely due to differences in particle composition, indoor particle infiltration, population characteristics, and methodological variations in exposure assessment and confounder control. 4. **Elemental Carbon and NO₂**: All-cause mortality was significantly associated with elemental carbon (pooled estimate per 1 μg/m³ 6% (95% CI 5-7%)) and NO₂ (pooled estimate per 10 μg/m³ 5% (95% CI 3-8%)), both markers of combustion sources. 5. **Coarse Particulate Matter**: Little evidence was found for an association between long-term coarse particulate matter exposure and mortality, possibly due to the small number of studies and limitations in exposure assessment. 6. **Susceptible Subgroups**: There was little evidence for stronger associations among women compared to men. Subjects with lower education and obesity experienced larger mortality effects related to fine PM, though the evidence for differences related to education has weakened in more recent studies. The review highlights the need for better exposure assessment methods, including spatially resolved outdoor exposures and chemically speciated particles, to better understand the heterogeneity in effect estimates and inform health impact assessments and air pollution control policies.This review examines the epidemiological evidence linking long-term exposure to ambient air pollution, particularly fine particulate matter (PM₂.₅), with mortality from all causes, cardiovascular disease, and respiratory disease. The authors conducted a meta-analysis of studies published up to January 2013, focusing on the effects of PM₂.₅, nitrogen dioxide (NO₂), and elemental carbon (EC). Key findings include: 1. **Mortality from All Causes**: A significant increase in mortality risk was observed with each 10 μg/m³ increase in PM₂.₅ exposure, with a pooled estimate of 6% (95% CI 4-8%) for all-cause mortality and 11% (95% CI 5-16%) for cardiovascular mortality. 2. **Mortality from Cardiovascular Disease**: Long-term exposure to PM₂.₅ was more strongly associated with cardiovascular mortality, particularly ischemic heart disease, compared to non-malignant respiratory diseases. The pooled estimate for cardiovascular mortality was 3% (95% CI -6, 13%). 3. **Heterogeneity in Effect Estimates**: Significant heterogeneity was found across studies, likely due to differences in particle composition, indoor particle infiltration, population characteristics, and methodological variations in exposure assessment and confounder control. 4. **Elemental Carbon and NO₂**: All-cause mortality was significantly associated with elemental carbon (pooled estimate per 1 μg/m³ 6% (95% CI 5-7%)) and NO₂ (pooled estimate per 10 μg/m³ 5% (95% CI 3-8%)), both markers of combustion sources. 5. **Coarse Particulate Matter**: Little evidence was found for an association between long-term coarse particulate matter exposure and mortality, possibly due to the small number of studies and limitations in exposure assessment. 6. **Susceptible Subgroups**: There was little evidence for stronger associations among women compared to men. Subjects with lower education and obesity experienced larger mortality effects related to fine PM, though the evidence for differences related to education has weakened in more recent studies. The review highlights the need for better exposure assessment methods, including spatially resolved outdoor exposures and chemically speciated particles, to better understand the heterogeneity in effect estimates and inform health impact assessments and air pollution control policies.