|Chemical or physical
rates of formation determine how far the precursor pollutants travel before
they begin forming secondary pollutants such as formaldehyde. Factors such as wind speed and temperature
will also influence where these secondary pollutants are formed, relative to
where they were originally emitted.
|The longer a
pollutant stays in the atmosphere, the farther it can be transported. Some air toxics are removed quickly by
chemical reactions (e.g., 1,3‑butadiene) or physical processes, (e.g., heavy
larger particles deposit to the ground quickly).
react more slowly and can travel large distances from where they are formed
or emitted (e.g., toxic metals in PM2.5). These pollutants may be more regionally