Evidence of recovery of Juniperus virginiana trees from sulfur pollution after the Clean Air Act.

Reply to Schaberg et al.: applying stable isotope analyses to examine the influence of acid deposition on Juniperus virginiana.

Our conclusion that a Juniperus virginiana stand in the central Appalachian Mountains is recovering from decades of acid deposition was based on tree ring carbon isotope ratios (δC) that show: (i) close correspondence between the timing of changes in direction of δC with declines in SO2 emissions occurring after the Clean Air Act; (ii) close similarities between patterns of δC after 1980 and du...

Inconclusive evidence of Juniperus virginiana recovery following sulfur pollution reductions.

Air pollution removal by urban trees and shrubs in the United States

A modeling study using hourly meteorological and pollution concentration data from across the coterminous United States demonstrates that urban trees remove large amounts of air pollution that consequently improve urban air quality. Pollution removal (O3, PM10, NO2, SO2, CO) varied among cities with total annual air pollution removal by US urban trees estimated at 711,000 metric tons ($3.8 bill...

Did the Clean Air Act Cause the Remarkable Decline in Sulfur Dioxide Concentrations?*

Over the last three decades, ambient concentrations of sulfur dioxide (SO2) air pollution have declined by approximately 80%. This paper tests whether the 1970 Clean Air Act and its subsequent amendments caused this decline. The centerpiece of this legislation is the annual assignment of all counties to SO2 nonattainment or attainment categories. Polluters face stricter regulations in nonattain...

Analysis of the physiological responses of the plane and willow trees against air pollution in Tehran .

Trees can improve air quality, but at the same time, pollution might put them at risk. Plane(Platanus orientalis L) and willow trees (Salix babylonicaL) are important trees in the green space of Tehran. Plane trees in Tehran have experienced early autumn in recent years due to severe air pollution. The present study, investigated some physiological traits of these trees under study to determine...