Techniques for treating an outside airflow with a direct evaporative economizer include circulating an airflow from an ambient environment into a direct evaporative economizer; circulating a cooling fluid into the direct evaporative economizer at a first rate so that a temperature condition of a supply airflow meets a predetermined range of setpoint temperatures; evaporating at least a portion of the cooling fluid circulated at the first rate into the airflow; determining that a measured air contaminant level of the airflow is greater than a setpoint contaminant level; and based on the determination, circulating the cooling fluid into the direct evaporative economizer at a second rate to precipitate a plurality of contaminants from the airflow into the cooling fluid, the second flow rate of the cooling fluid operable to adjust the temperature condition of the supply airflow outside of the predetermined range of setpoint temperatures of the supply airflow.