i'll let the experts explain it. Maybe just stick with the abstract written in bold
http://132.239.121.69/publications/ralph/3_Seasonal.pdf
Not my field, I'm just a simple man that looked at instruments for many years that can detect 1 part per billion of lets say So2, Co2, Nox, etc, for a living.
You said this is your field. I'll need you to explain the scientific language in the link you provided and put it in simple terms for me/us.