This work is an exploration of critical remaining questions in the field of pediatricair pollution epidemiology. Because children are uniquely susceptible and vulnerable to environmental exposures, a thorough understanding of the relationships between air pollution exposure and child health is needed. In this dissertation, I weigh in on three extant questions in pediatric air pollution epidemiology: (1) what are the different ways children might be affected by air pollution, (2) what are the long-term effects of children’s exposure, and (3) are there periods during which children are especially vulnerable? Chapter 2 is a systematic review summarizing new epidemiologic research associating ozone exposures with lung function, published during 2013-2020. Ozone effects on lung function are particularly important to understand in the context of the air pollution-health outcomes literature given the complex relationships between ozone and other air pollutants with known lung function effects. On March 18, 2018 and Sept 8, 2020 PubMed was searched using the terms “health AND ozone”, filtering to articles in English, about humans, from 2013 or later. Articles were selected for this review if they reported a specific relationship between a lung function outcome and ozone exposure. Of 3271 articles screened, 55 ultimately met criteria for inclusion. A systematic review with assessment of potential for bias was conducted, but a meta-analysis was not done because of differences in exposure duration and outcome quantification. There is consistent evidence of small decreases in children’s lung function, even associated with very low levels of short-term ozone exposure. The effects on adult lung function from exposure to low-level, short-term ozone are less clear, though there may be ozoneassociated decrements in the elderly. Finally, long-term ozone exposure decreases both lung function and lung function growth in children, though there are few new studies of 2 long-term ozone and lung function in adults. Much of this literature involves concentrations below the current US Environmental Protection Agency’s National Ambient Air Quality Standard of 70 ppb over an 8-hour averaging time, suggesting that this current standard may not adequately protect children from ozone-related decrements in lung function. Chapter 3 is a study of prenatal PM2.5 exposure and childhood IQ. Because PM2.5 is a ubiquitous environmental exposure, the potential for small changes in cognition associated with PM2.5 exposure could have great societal costs. Prior studies have demonstrated a relationship between in-utero PM2.5 exposure and cognitive development, but it is not known whether these effects are similar in rural populations and if they persist into late childhood/early adolescence. In this study I used IQ testing of the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) cohort at age 10.5 years, to test for an association between prenatal PM2.5 exposure and both full and subscale measures of IQ. A 3 μg/m3 increase in average PM2.5 over pregnancy was associated with a 1.79-point decrease in full-scale IQ (95% CI -2.96, -0.61), and subscale measures (Working Memory IQ (WMIQ) -1.65, 95% CI -2.98, -0.41; Processing Speed IQ (PSIQ) -1.34, 95% CI -2.66, -0.02). Flexible modeling over the course of pregnancy illustrated mid-to-late pregnancy (months 5-7) as particularly susceptible times, but with sex differences regarding which subscales were most affected (Verbal Comprehension IQ (VCIQ) and WMIQ in males, and PSIQ in females) and in the timing of susceptible windows (generally these occurred mid gestation in males and later gestation in females). Chapter 4 is a study of the association of multiple air pollutants and changing metabolic function in childhood. Previous studies have shown that air pollution exposure may contribute to metabolic dysfunction in childhood. However, little work is available on how air pollution relates to changes in metabolic parameters during childhood. In this study we assess growth in BMI percentile, waist-height ratio, systolic and diastolic blood pressure, hemoglobin A1c and high-density lipoprotein cholesterol between two assessments during childhood (approximately ages 8 and 10 years), in a cohort living in Fresno, CA. No relationship between changes in metabolic dysfunction and air pollution was found, despite high quality exposure data and power to detect clinically meaningful changes. Smaller changes in metabolic function may still be present and could be important for public health. Air pollutant exposure continues to adversely affect the health of children and ongoing efforts are needed both to further understand these effects and better protect children’s health.