Using nighttime air chemistry to track ozone impact

It is well known that the dog days of summer in St. Louis are hot, humid and hazy. On the warmest of these days, the air arrives from the south, bringing with it high temperatures, moisture and natural forest emissions of chemicals, known as hydrocarbons, from the Ozark Plateau. The hydrocarbons can interact with human-influenced emissions, and in the presence of sunlight, create a cocktail of pollutants—including ozone—that are hazardous to human health.