November 28, 2016
Although it might be a nuisance to drive through, fog, as it turns out, can be a helpful tool when determining what exactly is in the air we breathe.
In research just published in the journal Atmospheric Environment, Derek Straub, associate professor of earth and environmental sciences, reports on the organic and inorganic compounds he has found in fog collected at sites in Central Pennsylvania from 2007 to 2015.
The collection of samples by Straub and his students over multiple years makes this one of the few long-duration fog studies that have been completed.
"Fog is interesting," Straub said. "Droplets form on aerosol particles and they also absorb gasses, so it gives us a good idea of what's in the air we breathe."
Fog samples were collected at the Center for Environmental Education and Research (CEER) on the campus of Susquehanna University. Local emission sources include several uncontrolled coal combustion units. In addition, this area is influenced by agricultural emissions from fertilizer application and livestock. Transportation, home heating and industry sources are also present.
But first, how do you collect fog?
It's done through a collector that contains six rows of stainless steel rods. Air and fog droplets were drawn in by a fan located in the rear of the collector. The accumulated cloud droplets flowed down the rods and into a bottle. The collector is automated with a visibility monitor, so when fog would develop, it would trigger the collector to begin operating.
Of the 146 samples collected, the most abundant inorganic compounds found were ammonium (farms), sulfate (coal combustion) and nitrate (coal combustion and vehicle exhaust).
"Statistically significant decreasing trends from 2007 to 2015 were noted for sulfate, ammonium, chloride and nitrate," said Straub.
That's good news. He attributed the decrease to the closing of at least two coal-combustion facilities in 2014, and increasingly strict emissions regulations from the Environmental Protection Agency dating to the 1990s.
"The compounds found in fog are reflective of the overall chemical compounds in the atmosphere," Straub said. "It gives us an idea of what's out there, and can lead to additional legislative work, should science see these compounds creeping up in the future."