This is a report on magnetic properties of highroad-side tree (Pinus pumila Regel) leaves collected along an expressway linking Beijing City and the Capital International Airport and further focus on their environmental contributions. A series of rock magnetic experiments show that the primary magnetic mineral of leaf samples was identified to be magnetite, in the pseudo-single domain (PSD) grain size range 0.2-5.0μm. On the other hand, magnetite concentration and grain size in leaves are ascertained to decrease with increasing of sampling distance to highroad asphalt surface, suggesting that high magnetic response to traffic pollution is localized within a distance of some two meters away from highroad asphalt surface. Although magnetic susceptibility is ordinarily regarded as a simple, rapid and low-cost method for monitoring traffic pollution,saturation isothermal remanent magnetization (SIRM)can be treated as a valid proxy for monitoring air particulate matter (PM) when samples are magnetically weak. It is believed that a synthetic rock magnetic study is an effective method for determining concentration and grain size of ferromagnets in the atmospheric PM, and then it should be a rapid and feasible technique for monitoring atmospheric pollution.