Evaluation and improvements of two community models in simulating dry deposition velocities for peroxyacetyl nitrate (PAN) over a coniferous forest

The observed daytime maximum of V-d(PAN) was similar to 1.0 cm s(-1) on average, while the estimates by the WRF-Chem dry deposition module (WDDM) and the Noah land surface model coupled with a photosynthesis-based Gas Exchange Model (Noah-GEM) were only 0.2 cm s(-1) and 0.6 cm s(-1), respectively.

The observations also showed considerable PAN deposition at night with typical V-d values of 0.2-0.6 cm s(-1), while the estimated values from both models were less than 0.1 cm s(-1). Noah-GEM modeled more realistic stomatal resistance (R-s) than WDDM, as compared with observations of water vapor exchange fluxes. The poor performance of WDDM for stomatal uptake is mainly due to its lack of dependence on leaf area index.