Photography is based on chemical action induced by luminous rays; apart from this practical application there are many other cases in which actinic rays occasion chemical actions; these are treated in the article Photochemistry.
The method provides a very powerful and widely applicable method for studying the primary photochemistry of small gas phase molecules.
In the Northern Hemisphere, the summer maximum at polluted sites, such as Payerne, Hohenpeissenberg and Indiana is controlled by tropospheric photochemistry.
Our research group has made an intensive study of ozone photochemistry for more than thirty years.
A " snow photochemistry " is at work it seems.