Evolution of trace elements in the planetary boundary layer in southern China: Effects of dust storms and aerosol‐cloud interactions

Abstract

Aerosols and cloud water were analyzed at a mountaintop in the planetary boundary layer in southern China during March–May 2009, when two Asian dust storms occurred, to investigate the effects of aerosol‐cloud interactions (ACIs) on chemical evolution of atmospheric trace elements. Fe, Al, and Zn predominated in both coarse and fine aerosols, followed by high concentrations of toxic Pb, As, and Cd. Most of these aerosol trace elements, which were affected by dust storms, exhibited various increases in concentrations but consistent decreases in solubility. Zn, Fe, Al, and Pb were the most abundant trace elements in cloud water. The trace element concentrations exhibited logarithmic inverse relationships with the cloud liquid water content and were found highly pH dependent with minimum concentrations at the threshold of pH ~5.0. The calculation of Visual MINTEQ model showed that 80.7–96.3% of Fe(II), Zn(II), Pb(II), and Cu(II) existed in divalent free ions, while 71.7% of Fe(III) and 71.5% of Al(III) were complexed by oxalate and fluoride, respectively. ACIs could markedly change the speciation distributions of trace elements in cloud water by pH modification. The in‐cloud scavenging of aerosol trace elements likely reached a peak after the first 2–3 h of cloud processing, with scavenging ratios between 0.12 for Cr and 0.57 for Pb. The increases of the trace element solubility (4–33%) were determined in both in‐cloud aerosols and postcloud aerosols. These results indicated the significant importance of aerosol‐cloud interactions to the evolution of trace elements during the first several cloud condensation/evaporation cycles.

Chemical characteristics of cloud water and the impacts on aerosol properties at a subtropical mountain site in Hong Kong

“…The non-and semi-volatile species in cloud water at Mt. TMS including water-soluble ions, DOC, carboxylic acids and trace metals were inversely related to LWC in the power functions due to dilution effects, which have been widely observed in previous studies Li et al, 2017). Similar inverse-power relationships of water-soluble ions, DOC and carboxylic acids with pH were also found.…”

“…TMS (Lam et al, 2013), as different precursors could lead to different yields of glyoxal and methylglyoxal (Ervens et al, 2011). Aluminium (131.9 μg L -1 ) dominated the cloud water trace metals, of which the concentration was comparable to that measured at other mountain sites in China (Li et al, 2017). Abundant transition metals Fe (50.6 μg L -1 ), Cu (10.0 μg L -1 ) and Mn (5.9 μg L -1 ), which played important roles in the heterogeneous catalytical formation of sulfate (Harris et al, 2013), were also found.…”

In situ chemical composition measurement of individual cloud residue particles at a mountain site, southern China

“…At Mount Tai in northern China, a high concentration of Ca 2+ in cloud or fog water was mainly attributed to a sandstorm event during the spring season . At Mount Heng in southern China, the abundant crust-related elements (e.g., Al) observed in cloud water is due to Asian dust storms that occurred in March-May (Li et al, 2017). Based on the backward trajectory, the site was unlikely affected by sandstorm source in northwestern China during the cloud events.…”

An Evaluation of the CHIMERE Chemistry Transport Model to Simulate Dust Outbreaks across the Northern Hemisphere in March 2014

“…The model analysis showed that the formation of dust-nitrate occurred over the Yellow Sea and East China Sea before arriving in Japan. The mid-March episode was studied with the on-line coupled Weather Research and Forecasting-Chemistry (WRF-Chem) model over the Nanjing area focusing on the interactions between the dust load with the photochemistry [137]. Combined with observational data, the WRF-chem model has been recently used in a recent study [138] They show the dust plume located in the altitudes ranging from 1 km to 7 km over the source region, then ascended to 2-9 km over the Pacific Ocean.…”