Abstract
Abstract. The US Environmental Protection Agency's (EPA) Community Multiscale Air Quality (CMAQ) modeling system version 4.7 is further developed to enhance its capability in simulating the photochemical cycles in the presence of dust particles. The new model treatments implemented in CMAQ v4.7 in this work include two online dust emission schemes (i.e., the Zender and Westphal schemes), nine dust-related heterogeneous reactions, an updated aerosol inorganic thermodynamic module ISORROPIA II with an explicit treatment of crustal species, and the interface between ISORROPIA II and the new dust treatments. The resulting improved CMAQ (referred to as CMAQ-Dust), offline-coupled with the Weather Research and Forecast model (WRF), is applied to the April 2001 dust storm episode over the trans-Pacific domain to examine the impact of new model treatments and understand associated uncertainties. WRF/CMAQ-Dust produces reasonable spatial distribution of dust emissions and captures the dust outbreak events, with the total dust emissions of ~111 and 223 Tg when using the Zender scheme with an erodible fraction of 0.5 and 1.0, respectively. The model system can reproduce well observed meteorological and chemical concentrations, with significant improvements for suspended particulate matter (PM), PM with aerodynamic diameter of 10 μm, and aerosol optical depth than the default CMAQ v4.7. The sensitivity studies show that the inclusion of crustal species reduces the concentration of PM with aerodynamic diameter of 2.5 μm (PM2.5) over polluted areas. The heterogeneous chemistry occurring on dust particles acts as a sink for some species (e.g., as a lower limit estimate, reducing O3 by up to 3.8 ppb (~9%) and SO2 by up to 0.3 ppb (~27%)) and as a source for some others (e.g., increasing fine-mode SO42− by up to 1.1 μg m−3 (~12%) and PM2.5 by up to 1.4 μg m−3 (~3%)) over the domain. The long-range transport of Asian pollutants can enhance the surface concentrations of gases by up to 3% and aerosol species by up to 20% in the Western US.
Highlights
Natural and anthropogenic aerosols are known to play a significant role in human health, climate change, atmospheric visibility, stratospheric ozone depletion, acid deposition, and photochemical smog
Following the incorporation of the online dust emission module and dust-related heterogeneous chemistry, three new crustal species (i.e., Ca, K, and Mg) are added into Community Multiscale Air Quality (CMAQ) and the default thermodynamic module (i.e., ISORROPIA v1.7) in CMAQv4.7 is replaced by ISORROPIA II, to study the impact of those crustal species on the inorganic gas/particle partitioning through aerosol thermodynamic equilibrium
The discrepancies arise from several factors, including the slow responses of deep soil temperatures to synoptic-scale changes in air temperatures, the limitations of the planetary boundary layer (PBL) and land-surface schemes currently used in meteorological models in accurately simulating the airland heat fluxes (Gilliam et al, 2006), the limitation of Dudhia (1989) radiation scheme in simulating the longwave radiation, as well as the inability to resolve subgrid meteorological phenomena (Wang et al, 2009)
Summary
Natural and anthropogenic aerosols are known to play a significant role in human health, climate change, atmospheric visibility, stratospheric ozone depletion, acid deposition, and photochemical smog. It is incapable of reproducing observed mass concentrations of particulate matter with aerodynamic diameter less than or equal to 10 μm (PM10) and aerosol optical depths (AODs), due to the lack of mineral dust treatments in CMAQ (Wang et al, 2009; Wang and Zhang, 2010). In this study, this limitation is addressed by implementing an online dust emission and heterogeneous chemistry module into CMAQ version 4.7 in order to investigate the role of dust in affecting chemical predictions of air pollutants.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
