# Counterintuitive PM2.5 Increases During COVID-19 Lockdown in Ilo, Peru: Coastal Meteorology and Cardiovascular Implications

## TL;DR

This study found that PM2.5 pollution increased during the early reopening phase of the pandemic in Ilo, Peru, despite reduced human activity, due to coastal meteorological effects, which could lead to additional cardiovascular deaths.

## Contribution

The study provides novel evidence from a Latin American coastal city on how meteorology can counteract emission reductions, affecting public health outcomes.

## Key findings

- PM2.5 increased by 34% during early reopening in Ilo, despite reduced anthropogenic activity.
- O3 levels more than doubled in austral winter, with 98% of its variability attributed to meteorology.
- The PM2.5 increase was linked to an estimated 3 additional cardiovascular deaths per 100,000 people annually.

## Abstract

Public health relevance—How does this work relate to a public health issue?
Air pollution by fine particulate matter (PM2.5) is a leading environmental risk factor for cardiovascular mortality worldwide, with the Global Burden of Disease 2021 attributing approximately 7.8 million deaths annually to ambient PM2.5 exposure.The COVID-19 pandemic created a natural experiment to assess air quality responses to emission reductions, yet evidence from Latin American coastal industrial cities remains critically underrepresented in the global literature.

Air pollution by fine particulate matter (PM2.5) is a leading environmental risk factor for cardiovascular mortality worldwide, with the Global Burden of Disease 2021 attributing approximately 7.8 million deaths annually to ambient PM2.5 exposure.

The COVID-19 pandemic created a natural experiment to assess air quality responses to emission reductions, yet evidence from Latin American coastal industrial cities remains critically underrepresented in the global literature.

Public health significance—Why is this work of significance to public health?
Despite reduced anthropogenic activity during lockdown, PM2.5 increased by 34% during early reopening phases (16.9 vs. 12.6 µg/m3 baseline), while O3 more than doubled (+108%) in austral winter, demonstrating that coastal meteorology can counteract emission reduction benefits.Variance decomposition revealed that O3 variability was almost entirely meteorology-driven (98%), while PM2.5 and NO2 showed balanced contributions from meteorology and COVID-19 restrictions (~50% each), highlighting the critical need for meteorological normalization in air quality policy evaluation.

Despite reduced anthropogenic activity during lockdown, PM2.5 increased by 34% during early reopening phases (16.9 vs. 12.6 µg/m3 baseline), while O3 more than doubled (+108%) in austral winter, demonstrating that coastal meteorology can counteract emission reduction benefits.

Variance decomposition revealed that O3 variability was almost entirely meteorology-driven (98%), while PM2.5 and NO2 showed balanced contributions from meteorology and COVID-19 restrictions (~50% each), highlighting the critical need for meteorological normalization in air quality policy evaluation.

Public health implications—What are the key implications or messages for practi-tioners, policy makers and/or researchers in public health?
The PM2.5 increase during lockdown corresponded to approximately 3 additional cardiovascular deaths per 100,000 population annually, emphasizing that counterintuitive air quality responses can translate into measurable health burdens requiring location-specific intervention strategies.Temporary emission reduction policies alone are insufficient to achieve health-protective air quality in coastal industrial cities; integrated strategies must account for local meteorological dynamics, marine boundary layer effects, and non-linear atmospheric chemistry.

The PM2.5 increase during lockdown corresponded to approximately 3 additional cardiovascular deaths per 100,000 population annually, emphasizing that counterintuitive air quality responses can translate into measurable health burdens requiring location-specific intervention strategies.

Temporary emission reduction policies alone are insufficient to achieve health-protective air quality in coastal industrial cities; integrated strategies must account for local meteorological dynamics, marine boundary layer effects, and non-linear atmospheric chemistry.

The COVID-19 pandemic created a natural experiment to assess air quality responses to emission reductions, yet evidence from Latin American coastal industrial cities remains scarce. This study examined how meteorological variability modulated the effects of COVID-19 restrictions on air quality in Ilo, a medium-sized coastal industrial city in southern Peru (~67,000 inhabitants). We analyzed daily concentrations of PM10, PM2.5, NO2, O3, and SO2 across six pandemic phases (January–December 2020) using multiple linear regression, variance decomposition, and Random Forest models. A health impact assessment translated PM2.5 changes into cardiovascular mortality estimates using Global Burden of Disease 2021 coefficients. Despite reduced anthropogenic activity, PM2.5 increased by 34% during early reopening (May–June: 16.9 vs. 12.6 µg/m3 baseline), whereas NO2 decreased consistently (13–19%), SO2 declined up to 65%, and O3 more than doubled (+108%) in austral winter. Variance decomposition revealed that O3 variability was almost entirely meteorology-driven (98%), while PM2.5 and NO2 showed balanced contributions from meteorology and restrictions (~50% each). The PM2.5 increase corresponded to approximately 3 additional cardiovascular deaths per 100,000 population annually. Coastal meteorology can counteract emission reductions, generating counterintuitive air quality responses and underscoring the need for meteorological normalization in policy evaluation.