I have a vocabulary question. How can air smell spectrally? As in:

"From the darkness of a box in the Nevada desert, he watched as three men trudged down a dirt road in Afghanistan. The box was kept cold—precisely sixty-eight degrees—and the only light inside came from the glow of monitors. The air smelled spectrally of stale sweat and cigarette smoke. On his console, the image showed the midwinter landscape of eastern Afghanistan’s Kunar Province—a palette of browns and grays, fields cut to stubble, dark forests climbing the rocky foothills of the Hindu Kush."

Thank you.