Columbia subject headings:
Air--Pollution--Arizona--Grand Canyon.
Haze--Arizona--Grand Canyon.
Harvard subject headings:
Air--Pollution--Arizona--Grand Canyon National Park--Experiments.
Grand Canyon National Park (Ariz.)
Winter Haze Intensive Tracer Experiment--Evaluation.
Princeton subject headings:
Air--Pollution--Arizona--Grand Canyon.
Haze--Arizona--Grand Canyon.