SUMMARY Project Title: Long-term Effects of a household Air Pollution intervention: Follow-up of a randomized controlled trial Globally, nearly 3 billion people are exposed to household air pollution (HAP) from the use of solid fuels (biomass or coal) for cooking and heating. In 2019, HAP accounted for an estimated 2.3 million premature deaths and 3.6% of global disability-adjusted life years lost. As a strategy to mitigate HAP and improve health outcomes, we recently completed an 18-month intervention of liquefied petroleum gas (LPG) stoves and fuel (HAPIN trial; UM1HL134590, MPIs: Checkley, Clasen, Peel), however current evidence suggests that the health benefits of HAP reduction may not become apparent until several years later. Leveraging the participant cohort and comprehensive data collected in the HAPIN trial, we seek to determine the long- term effects of an 18-month LPG stove, continuous fuel and behavioral messaging intervention on health outcomes among children in Puno, Peru (n=709). We will measure clinical outcomes, kitchen concentrations and personal exposures to PM2.5 once yearly and monitor biomass cooking stoves continuously using temperature loggers throughout the study period. We will examine whether health outcomes of intervention participants (lung function, cardiovascular risk profile, and neurodevelopmental outcomes) differ to those from control households through age eight and conduct exposure-response analyses based on the PM2.5 exposure and stove use data during the intervention and subsequent follow-up period. Additionally, we will evaluate if intervention households continue to use LPG for a higher percentage of cooking time than controls and to experience lower PM2.5 exposures. This study will provide valuable insight on the longer-term effects of HAP mitigation during a critical period of child development and generate evidence which can inform government policies for clean fuel intervention programs. Moreover, it will contribute unique data on pediatric lung function measures and childhood cardiovascular disease risk, which is currently limited in low- and middle-income countries.