Atmospheric removal of PM_2.5 by man-made Three Northern Regions Shelter Forest in Northern China estimated using satellite retrieved PM_2.5 concentration

Atmospheric removal of PM_2.5 by the Three Northern Regions Shelter Forest (TNRSF) - the so called Green Great Wall (GGW) in northern China through dry deposition process was estimated using a bulk big-leaf model and a vegetation collection model. Decadal trend of PM_2.5 dry deposition flux from 1999 to 2010 was calculated from modeled dry deposition velocity and air concentration retrieved from the satellite remote sensing. Dry deposition velocities of PM_2.5 calculated using the two deposition models increased in many places of the TNRSF over the last decade due to increasing vegetation coverage of the TNRSF. Both increasing deposition velocity due to forest expansion and PM_2.5 atmospheric level contributed to the increasing deposition flux of PM_2.5. The highest atmospheric deposition flux of PM_2.5 was found in the Central-north region covering Beijing-Tianjin-Hebei area, followed by the Northwestern and the Northeastern regions of the TNRSF. While greater collection of PM_2.5 by vegetation was identified in the Northeastern region of the TNRSF due to higher forest coverage over this region, the most significant incline of the PM_2.5 atmospheric removal due to vegetation collection was discerned in the Central-north region because of the most rapid increase in the vegetation coverage in this region. A total mass of 2.85×10⁷t PM_2.5 was estimated to be removed from the atmosphere through dry deposition process over the TNRSF from 1999 to 2010. The two deposition models simulated similar magnitude and spatial patterns of PM_2.5 dry deposition fluxes. Our results suggest that the TNRSF plays a moderate role in PM_2.5 uptake, but enhances PM_2.5 atmospheric removal by 30% in 2010 than in 1980.