Three‐dimensional simulations of inorganic aerosol distributions in east Asia during spring 2001

Abstract

[1] In this paper, aerosol composition and size distributions in east Asia are simulated using a comprehensive chemical transport model. Three-dimensional aerosol simulations for the TRACE-P and ACE-Asia periods are performed and used to help interpret actual observations. The regional chemical transport model, STEM-2K3, which includes the on-line gas-aerosol thermodynamic module SCAPE II, and explicitly considers chemical aging of dust, is used in the analysis. The model is found to represent many of the important observed features. The Asian outflow during March and April of 2001 is heavily polluted with high aerosol loadings. Under conditions of low dust loading, SO 2 condensation and gas phase ammonia distribution determine the nitrate size and gas-aerosol distributions along air mass trajectories, a situation that is analyzed in detail for two TRACE-P flights. Dust is predicted to alter the partitioning of the semivolatile components between the gas and aerosol phases as well as the size distributions of the secondary aerosol constituents. Calcium in the dust affects the gas-aerosol equilibrium by shifting the equilibrium balance to an anion-limited status, which benefits the uptake of sulfate and nitrate, but reduces the amount of aerosol ammonium. Surface reactions on dust provide an additional mechanism to produce aerosol nitrate and sulfate. The size distribution of dust is shown to be a critical factor in determining the size distribution of secondary aerosols. As much of the dust mass is found in the supermicron mode (70-90%), appreciable amounts of sulfate and nitrate are found in the supermicron particles. For sulfate the observations and the analysis indicate that 10-30% of sulfate is in the supermicron fraction during dust events; in the case of nitrate, more than 80% is found in the supermicron fraction.

An evaluation of real‐time air quality forecasts and their urban emissions over eastern Texas during the summer of 2006 Second Texas Air Quality Study field study

“…In this experiment, the STEM-2K3 model included aerosols in four size bins (in diameter): 0.1-0.3 mm, 0.3-1.0 mm, 1.0-2.5 mm, and 2.5-10 mm [Tang et al, 2004]. Thirty photolysis frequencies required for the SAPRC-99 mechanism are explicitly treated online taking into account the influence of aerosols and clouds [Tang et al, 2003].…”

“…This model has been generalized to simulate regional air quality [Tang et al, 2003;Carmichael et al, 2003;Tang et al, 2004], and the latest version is used here. During the TexAQS II experiment, STEM-2K3 provided a multiscale forecast, including a primary domain with 60-km horizontal resolution covering the contiguous United States, and a nested 12-km domain covering Texas.…”

Role of dust alkalinity in acid mobilization of iron

“…Ito and Y. Feng: Role of dust alkalinity in acid mobilization of iron other hand, mineral dust aerosols originating from the Asian deserts may exhibit a strong buffering ability by neutralizing the acidic pollutants encountered during the long-range transport (Iwasaka et al, 1988;Carmichael, 1999, 2001;Tang et al, 2004). Recently, McNaughton et al (2008) and Fairlie et al (2009) have argued that dust does not acidify in the free troposphere generally.…”

Characteristics and composition of the falling dust in urban environment

“…This discrepancy could show that emissions of NO X are not merely the source of dust nitrate. Previous studies repeatedly reported that the formations of particulate sulfate and nitrate on sea salt particles (Eriksson 1959;McInnes et al 1994) and dust particles enhanced the production of particulate sulfate and nitrate in the downstream atmosphere (Nishikawa et al 1991;Dentener 1996;Tang 2004). The sea is about 2-3 km from the tested area, which is where the particles could have originated from, and the wind could have induced the transportation.…”