Heterogeneous chemistry of individual mineral dust particles with nitric acid: A combined CCSEM/EDX, ESEM, and ICP‐MS study

Abstract

[1] The heterogeneous chemistry of individual dust particles from four authentic dust samples with gas phase nitric acid was investigated in this combined computer-controlled scanning electron microscopy with energy-dispersive X-ray (CCSEM/EDX) analysis, environmental scanning electron microscopy (ESEM), and inductively coupled plasma mass spectrometry (ICP-MS) study. Morphology and compositional changes of individual particles as they react with nitric acid were observed using conventional scanning electron microscopy with energy-dispersive X-ray analysis and CCSEM/EDX. ESEM was utilized to investigate the hygroscopic behavior of mineral dust particles reacted with nitric acid. Differences in the reactivity of mineral dust particles from these four different dust source regions with nitric acid were observed. Mineral dust from source regions containing high levels of calcium, namely, China loess dust and Saudi coastal dust, were found to react to the greatest extent. In particular, we show that calcium carbonate rich dust aerosols may exhibit continuous, extensive reactivity with nitric acid resulting in formation of highly hygroscopic calcium nitrate particles. Transformation of dry mineral dust into an aqueous liquid aerosol has a tremendous impact on its light scattering properties, ability to modify clouds, heterogeneous chemistry, and gas to particle partitioning in the atmosphere. ICP-MS was used to estimate maximal extent of possible CaCO 3 -to-Ca(NO 3 ) 2 conversion in the mineral dust samples. We show that in China loess dust and Saudi coastal dust aerosols, formation of calcium nitrate particles can take place at the total extent as high as $20-40 wt %.

Influence of dust composition on cloud droplet formation

“…Alpert and Ganor (2001) reported high carbonate content (29% CaCO 3 , 26% CaMg(CO 3 ) 2 ) for non-clay minerals sampled in Israel that appeared to originate from Algeria, Libya, and Israel. Laskin et al (2005) found little carbonate in Saharan and inland Saudi Arabian soil, but significant carbonate in soil from coastal Saudi Arabia and China. Given the regional differences in carbonate content, we consider a range of compositions.…”

“…During transport, CaCO 3 in dust can react with gases such as HNO 3 and SO 2 to form components that may enhance dust's ability to serve as CCN. The main product of the HNO 3 reaction is calcium nitrate, which deliquesces at low RH and greatly enhances dust 8/21/2006 hygroscopicity (Laskin et al, 2005). In the case of the SO 2 reaction with CaCO 3 , calcium sulfite appears to form, and the sulfite can be oxidized to sulfate by gas-phase ozone (Usher et al, 2002).…”

Inorganic salts interact with oxalic acid in submicron particles to form material with low hygroscopicity and volatility

“…For these particles, solubilizing reactions, such as uptake of nitric acid, may occur at the particle surface, and subsequent water exposure creates conditions ripe for reaction between OxA and di-valent cations (Laskin et al, 2012). Surface reactions between oxalic acid and metal chlorides can produce highly volatile hydrochloric acid, and evaporation of HCl will drive the in-particle equilibrium towards formation of the insoluble M-Ox complex (Laskin et al, 2005). Loss of volatile products occurs at the particle surface, leading to enrichment of the remaining lower volatility material at the particle surface.…”

Morphological and chemical modification of mineral dust: Observational insight into the heterogeneous uptake of acidic gases

“…[17] Krueger et al [2004] and Laskin et al [2005a] experimented on authentic dust in a laboratory and demonstrated that calcites (CaCO 3 ) can react with gaseous HNO 3 to form Ca(NO 3 ) 2 , which can then deliquesce even under conditions as dry as RH < 12%. Ca-rich spherical particles found frequently in the Beijing atmosphere might well be the modified product of carbonate formed in this manner.…”