How do biogenic emissions impact HOx radical chemistry in the near-canopy environment?
Because of their central role in atmospheric chemistry, measurements of OH and HO2 can provide a critical test of fast atmospheric photochemistry (Heard and Pilling, 2003). Recent measurements have shown serious discrepancies between measured and modeled levels of OH and HO2, especially in forest environments, bringing into question the understanding of HOx photochemistry and of the contribution of BVOC emissions to the chemistry of O3 and SOA production. Measurements of OH at PROPHET in 1998 using Laser Induced Fluorescence (LIF) were 2.7 times greater than concentrations predicted using a constrained photochemical model, while measured HO2 concentrations were generally in good agreement with the model (Tan et al., 2001). This discrepancy in the HO2/OH ratio suggests that the understanding of the chemistry controlling HOx is incomplete under conditions of low [NOx] and high BVOC emissions. Similar results were obtained in a forested environment in Greece, where modeled OH was 50% lowe
