In Anchorage, Alaska, particulates with aerodynamic diameter ⩽10μm (PM 10 ) arise primarily from natural, geologic sources, and particulates with aerodynamic diameter ⩽2.5μm (PM 2.5 ) arise primarily from automobile emissions. The current study used a population-based time-series analysis design to evaluate the effects of daily and weekly PM 10 and PM 2.5 on respiratory health outcomes among children <20 years of age residing in Anchorage enrolled in Medicaid. All generated estimating equations models were adjusted for season, year, weekends, temperature, wind speed, and precipitation. Relative to the days with PM 10 mass concentration ⩽13μg/m 3 , a significant 9.3% increase (RR: 1.093, 95% CI: 1.004–1.191) in the rate of outpatient visits for asthma occurred during days with PM 10 of 20–33μg/m 3 . No further dose–response occurred for days with PM 10 ⩾34μg/m 3 . A significant 18.1% increase (RR: 1.181, 95% CI: 1.010–1.381) in the rate of quick-relief medication prescriptions occurred during days with PM 10 of 34–60μg/m 3 , and a 28.8% increase (RR: 1.288, 95% CI: 1.026–1.619) occurred during days with PM 10 ⩾61μg/m 3 . Similar results for outpatient asthma visits and quick-relief medication occurred in weekly models. There were no significant associations with PM 2.5 in either daily or weekly models. These subtle but statistically significant associations suggest that non-industrial, geologic sources of PM 10 may have measurable health effects at levels below current national standards.