Abstract
Abstract. The Community Multiscale Air Quality (CMAQ) model has been further developed in terms of simulating natural wind-blown dust in this study, with a series of modifications aimed at improving the model's capability to predict the emission, transport, and chemical reactions of dust. The default parameterization of initial threshold friction velocity constants are revised to correct the double counting of the impact of soil moisture in CMAQ by the reanalysis of field experiment data; source-dependent speciation profiles for dust emission are derived based on local measurements for the Gobi and Taklamakan deserts in East Asia; and dust heterogeneous chemistry is also implemented. The improved dust module in the CMAQ is applied over East Asia for March and April from 2006 to 2010. The model evaluation result shows that the simulation bias of PM10 and aerosol optical depth (AOD) is reduced, respectively, from −55.42 and −31.97 % by the original CMAQ to −16.05 and −22.1 % by the revised CMAQ. Comparison with observations at the nearby Gobi stations of Duolun and Yulin indicates that applying a source-dependent profile helps reduce simulation bias for trace metals. Implementing heterogeneous chemistry also results in better agreement with observations for sulfur dioxide (SO2), sulfate (SO42−), nitric acid (HNO3), nitrous oxides (NOx), and nitrate (NO3−). The investigation of a severe dust storm episode from 19 to 21 March 2010 suggests that the revised CMAQ is capable of capturing the spatial distribution and temporal variation of dust. The model evaluation also indicates potential uncertainty within the excessive soil moisture used by meteorological simulation. The mass contribution of fine-mode particles in dust emission may be underestimated by 50 %. The revised CMAQ model provides a useful tool for future studies to investigate the emission, transport, and impact of wind-blown dust over East Asia and elsewhere.
Highlights
Natural dust has a wide impact on many different aspects of the Earth’s system
With the revised dust scheme, the Community Multiscale Air Quality (CMAQ) generally reproduces the spatial distribution of Asian dust as shown in Fig. 3b, which indicates the most significant impact over northern and east
The initial threshold friction velocity constants are revised by removing the double counting of soil moisture in the default parameters; two source-dependent speciation profiles are derived based on local observations of dust emission from the Taklamakan and Gobi deserts; and dust heterogeneous chemistry is implemented
Summary
Natural dust has a wide impact on many different aspects of the Earth’s system. It reduces atmospheric visibility (Engelstaedter et al, 2003; Kurosaki and Mikami, 2005; Washington et al, 2003), deteriorates air quality (De Longueville et al, 2010; Prospero, 1999), alters the radiative forcing budget (Liao et al, 2004; Miller et al, 2006; Reddy et al, 2005), and affects the cloud properties and precipitation (Rosenfeld et al, 2001; Forster et al, 2007). Over East Asia, spring time dust storms often lead to severe air pollution since the intensively elevated aerosol loadings are dumped over the most populated areas. Fu et al.: Model development of dust emission and heterogeneous chemistry
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