The impact of trees on urban air quality is not all bad. Park
and Schade (2016) demonstrate that tree photosynthesis in
urban green space was able to offset a fraction of the CO2 emitted
from traffic combustion engines, and ecosystem respiration
in Houston, TX. This study provides evidence of a strong correlation
between the urban CO2 emission rates in spring and
summer as measured by eddy covariance and the photosynthetically
active radiation on the same days.