Fine particulate matter (PM2.5) pollution is a significant global health concern, linked to various adverse health outcomes, including increased mortality. While much research exists on this topic, it predominantly focuses on developed countries with relatively lower pollution levels and different demographics than many parts of the world. Chile, a developing OECD nation, presents a unique opportunity to study this relationship due to its high PM2.5 concentrations exceeding WHO guidelines in many cities. Prior research in Chile has used limited ground-based monitoring data, focusing primarily on urban centers, leaving a significant gap in our understanding of the effects across the entire country, including rural areas. This study leverages recent advancements in satellite-based PM2.5 measurement technology to obtain comprehensive spatial and temporal coverage, allowing for a more complete analysis of the relationship between short-term PM2.5 exposure and mortality among the elderly (75+) population in Chile. This age group is particularly vulnerable to PM2.5 exposure, and understanding the impacts is critical given the rapidly aging population in low-and middle-income countries like Chile. The study aims to address the scarcity of research on the short-term effects of PM2.5 exposure in rural areas and to assess the effect size across different geographic, socioeconomic, and temporal dimensions. The use of detailed commune-level data provides insights into regional heterogeneity not previously investigated.

Numerous studies have established the adverse health effects of PM2.5 exposure, including cardiovascular and respiratory diseases and increased mortality. Research has shown that older populations and infants are especially vulnerable. However, most existing research is concentrated in developed countries with more readily available data and lower pollution levels. These studies often have limitations in terms of geographical coverage and the inability to fully explore heterogeneity based on rural vs. urban settings, income, or baseline pollution levels. The application of satellite-based PM2.5 data has enabled researchers to expand the scope of studies to include developing countries and regions with sparse ground-level monitoring. However, the limited duration of some satellite-based studies has impeded the full exploration of temporal effects and potential adaptation. Previous studies in Chile have primarily focused on cities using ground-level monitoring stations, limiting the geographical scope of analysis and the potential to study rural areas and the complete heterogeneity of impacts. The current study addresses the need for more comprehensive studies on the impact of short-term PM2.5 exposure on elderly mortality in a developing country, utilizing the detailed spatial and temporal data provided by satellite imagery.

This study employs a comprehensive methodology to investigate the short-term effects of PM2.5 pollution on elderly mortality in Chile. The study area covers the continental area of Chile, utilizing commune-level data as the primary geographical unit of analysis. Data were collected and analyzed from 2002 to 2019 to encompass a substantial time frame while excluding the COVID-19 pandemic. For PM2.5 exposure, satellite-based data from the Atmospheric Composition Analysis Group (ACAG) at Washington University in St. Louis were used, providing estimates at a high spatial resolution (0.01°). These satellite estimates were validated using ground-based measurements from Chile's National Air Quality Information System (SINCA), and the comparison revealed a 0.78 Pearson correlation coefficient, but with regional variations in accuracy, particularly in under- and overestimating low and high concentrations. Land temperature data were sourced from the Terra Moderate Resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature/Emissivity Daily (MOD11A1). Population data from the National Statistics Institute of Chile (INE) and mortality data from the Chilean Department of Statistics and Health Information (DEIS) were also used. The researchers estimated population-weighted PM2.5 and temperature exposures at the commune-month level, combining satellite data with finer-grained population data from the 2017 census. Monthly mortality rates for individuals aged 75 and older were calculated for all causes of death, as well as for specific causes such as cardiorespiratory, cardiovascular, and respiratory causes, based on ICD-10 codes. To analyze the relationship between PM2.5 exposure and mortality, the researchers used a generalized linear model with negative binomial distribution, accounting for commune-specific and quarter-year fixed effects. Sensitivity analyses were conducted to assess the robustness of the findings using alternative model specifications, including Poisson and ordinary least squares models. The analyses explored heterogeneity in the relationship between PM2.5 and mortality across various dimensions such as region, urban/rural areas, baseline pollution levels, income quintiles, and the share of the population aged 75+. The study also estimated avoided deaths under the hypothetical scenarios where PM2.5 concentrations met national standards (20 µg/m³) and WHO guidelines (5 µg/m³).

The study's key finding is a statistically significant positive association between short-term PM2.5 exposure and all-cause mortality among individuals aged 75+ in Chile. Specifically, a 10 µg/m³ increase in monthly PM2.5 exposure is associated with a 1.7% increase (95% CI: 1.1–2.4%) in monthly all-cause mortality. This overall effect masks substantial spatial heterogeneity. Eight of the sixteen regions in Chile, primarily located in the center-south, show significant positive associations. The Metropolitan region, containing Santiago, exhibits a significantly larger effect (5.3%, 95% CI: 4.2–6.5%). The effect size is remarkably consistent across different demographic and socioeconomic groups, including baseline PM2.5 levels, urban/rural areas, income quintiles, and over the 18-year study period. However, a larger effect is seen for communes with population shares of 75+ individuals above the median. The analysis also provides estimates of avoided deaths if the country were to achieve either the national standard (20 µg/m³) or the WHO guideline (5 µg/m³) for PM2.5. Under the WHO guideline scenario, an estimated 126 avoided deaths per month (or over 25,000 deaths over the study period) could have been achieved. The analysis of specific causes of death shows the most significant effects for respiratory causes, followed by all-cause mortality (excluding cardiorespiratory), cardiorespiratory, and cardiovascular causes. Urban areas show a slightly larger effect on respiratory causes than rural areas.

The findings of this study strongly support the negative impact of short-term PM2.5 exposure on elderly mortality in Chile. The consistent effect across numerous dimensions highlights the pervasive nature of this public health challenge. The observed geographical heterogeneity, with the most substantial effects in the center-south and metropolitan regions, suggests the importance of targeted interventions in these areas. While the study controls for several potential confounders, the consistently positive effects suggest a causal relationship between short-term PM2.5 exposure and increased mortality in the elderly population. The estimated avoided deaths under different PM2.5 reduction scenarios illustrate the significant public health benefits achievable through effective air quality policies. The consistency of the findings across diverse socioeconomic and demographic groups emphasizes the importance of comprehensive pollution control measures.

This research demonstrates a significant association between short-term PM2.5 exposure and increased mortality among the elderly in Chile, particularly in the center-south and metropolitan regions. The findings underscore the need for robust air quality regulations and interventions to reduce PM2.5 pollution and its associated health risks. Future research could explore the influence of PM2.5 source composition and indoor air pollution, given their potential to modify the relationship between outdoor PM2.5 exposure and mortality. Furthermore, investigation into the mechanisms underlying the observed regional heterogeneity and potential adaptations of the population over time would enhance our understanding of this public health issue.

The study has several limitations. The validation of satellite-based PM2.5 estimates reveals some inaccuracies, particularly in the lower and higher concentration ranges, which could potentially introduce bias into the effect size estimates. Both satellite and ground-based PM2.5 measurements primarily capture outdoor pollution, neglecting indoor sources. Indoor PM2.5 exposure is likely more significant for the elderly, especially in colder regions, where wood burning is prevalent. The lack of data on PM2.5 source composition limits the ability to assess how different sources might affect health outcomes. Finally, using commune of residence at death may not perfectly reflect exposure throughout an individual's lifetime. Despite these limitations, the study provides valuable insights into a crucial public health concern.