Posted by sally kentch on April 28, 2008

Q: If trees/leaves clean the air, then do pollution levels go up during the winter months when the deciduous trees lose their leaves? AND do evergreen trees help with reducing air pollution?

State: Washington

A: Your question is an excellent one Sally. I never thought about the difference between summer, when leaves are on the trees and winter, when they're not and am glad you asked.

# The Maryland Department of Natural Resources Forest Service describes how trees reduce air pollution as follows: Help to settle out, trap and hold particle pollutants (dust, ash, pollen and smoke) that can damage human lungs.

# Absorb CO2 and other dangerous gasses and, in turn, replenish the atmosphere with oxygen.

# Produce enough oxygen on each acre for 18 people every day.

# Absorb enough CO2 on each acre, over a year's time, to equal the amount you produce when you drive your car 26,000 miles. Trees remove gaseous pollutants by absorbing them through the pores in the leaf surface. Particulates are trapped and filtered by leaves, stems and twigs, and washed to the ground by rainfall

Based on Maryland's list, it makes complete sense to me that winter air pollution levels would rise without leaves on deciduous trees. Although evergreen trees have needles, rather than large "typical" leaves, they also fulfill the air pollution reduction that is described. In winter evergreen trees do photosynthesis, but to a lesser extent than in summer so they also contribute, to some degree, in reducing air pollution.

Hope this helps and thanks for your thought-provoking question.

John Wiessinger ( April 29, 2008)