Ammonia, ammonium, and the risk of asthma: A register-based case–control study in Danish children

Background:Evidence concerning the health effectsof exposure to fine particulatematter less than 2.5 μm in diameter (PM2.5) and particulatecomponents such as ammonium(NH4+) is limited. We aimed to investigate gaseous ammonia (NH3), particulate ammonium(NH4+), the total concentration of these po