Field observation on secondary organic aerosols during Asian dust storm periods: Formation mechanism of oxalic acid and related compounds on dust surface

We present a sensitivity study on transatlantic dust transport, a process which has many implications for the atmosphere, the ocean and the climate. We investigate the impact of key processes that control the dust outflow, i.e., the emission flux, convection schemes and the chemical aging of mineral dust, by using the EMAC model following Abdelkader et al. (2015). To characterize the dust outflow over the Atlantic Ocean, we distinguish two geographic zones: (i) dust interactions within the Intertropical Convergence Zone (ITCZ), or the dust–ITCZ interaction zone (DIZ), and (ii) the adjacent dust transport over the Atlantic Ocean (DTA) zone. In the latter zone, the dust loading shows a steep and linear gradient westward over the Atlantic Ocean since particle sedimentation is the dominant removal process, whereas in the DIZ zone aerosol–cloud interactions, wet deposition and scavenging processes determine the extent of the dust outflow. Generally, the EMAC simulated dust compares well with CALIPSO observations; however, our reference model configuration tends to overestimate the dust extinction at a lower elevation and underestimates it at a higher elevation. The aerosol optical depth (AOD) over the Caribbean responds to the dust emission flux only when the emitted dust mass is significantly increased over the source region in Africa by a factor of 10. These findings point to the dominant role of dust removal (especially wet deposition) in transatlantic dust transport. Experiments with different convection schemes have indeed revealed that the transatlantic dust transport is more sensitive to the convection scheme than to the dust emission flux parameterization. To study the impact of dust chemical aging, we focus on a major dust outflow in July 2009. We use the calcium cation as a proxy for the overall chemical reactive dust fraction and consider the uptake of major inorganic acids (i.e., H2SO4, HNO3 and HCl) and their anions, i.e., sulfate (SO42−), bisulfate (HSO4−), nitrate (NO3−) and chloride (Cl−), on the surface of mineral particles. The subsequent neutralization reactions with the calcium cation form various salt compounds that cause the uptake of water vapor from the atmosphere, i.e., through the chemical aging of dust particles leading to an increase of 0.15 in the AOD under subsaturated conditions (July 2009 monthly mean). As a result of the radiative feedback on surface winds, dust emissions increased regionally. On the other hand, the aged dust particles, compared to the non-aged particles, are more efficiently removed by both wet and dry deposition due to the increased hygroscopicity and particle size (mainly due to water uptake). The enhanced removal of aged particles decreases the dust burden and lifetime, which indirectly reduces the dust AOD by 0.05 (monthly mean). Both processes can be significant (major dust outflow, July 2009), but the net effect depends on the region and level of dust chemical aging

show abstract

“…-Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO); Winker et al (2009Winker et al ( , 2007;…”

Section: Long-term Evaluationmentioning

confidence: 99%

Sensitivity of transatlantic dust transport to chemical aging and related atmospheric processes

et al. 2017

View full text Add to dashboard Cite

show abstract

“…Journal of Geophysical Research: Atmospheres 10.1002/2016JD026246 C 2 can be produced by the oxidation of normal-chain diacids (C 3 -C 12 ) in aqueous-phase via heterogeneous reaction on the deliquesced coarse mode aerosols [Yang et al, 2009;Wang et al, 2015]. Interestingly, good correlations of C 2 with C 3 -C 5 diacids (r = 0.68-0.91) were found in coarse mode, indicating that they might have similar sources and formation processes and C 2 may be produced by the sequential aqueous-phase oxidation of its higher homologous diacids in coarse mode aerosols.…”

Section: Dicarboxylic Acidsmentioning

confidence: 99%

Sources and formation processes of water‐soluble dicarboxylic acids, ω‐oxocarboxylic acids, α‐dicarbonyls, and major ions in summer aerosols from eastern central India

et al. 2017

View full text Add to dashboard Cite

The sources and formation processes of dicarboxylic acids are still under investigation. Size‐segregated aerosol (nine‐size) samples collected in the urban site (Raipur: 21.2°N and 82.3°E) in eastern central India during summer of 2013 were measured for water‐soluble diacids (C2‐C12), ω‐oxoacids (ωC2‐ωC9), α‐dicarbonyls (C2‐C3), and inorganic ions to better understand their sources and formation processes. Diacids showed the predominance of oxalic acid (C2), whereas ω‐oxoacids showed the predominance of glyoxylic acid (ωC2), and glyoxal (Gly) was a major α‐dicarbonyl in all the sizes. Diacids, ω‐oxoacids, and α‐dicarbonyls as well as SO42prefix−, NO3−, and normalNnormalH4+ were enriched in coarse mode, where Ca2+ peaked, suggesting that they are preferentially produced in coarse mode via adsorption as well as heterogeneous and aqueous‐phase oxidation reaction of precursors on the surface of water‐soluble mineral dust particles having more alkaline species. Strong correlations of diacids and related compounds with NO3− (r = 0.66–0.91) and aerosol water content (AWC) (r = 0.63–0.93) further suggest the importance of heterogeneous and aqueous‐phase production in coarse mode. We found strong correlations of C2/(C2‐C12), C2/ωC2, and C2/Gly ratios with AWC in coarse mode (r = 0.83, 0.86, and 0.85, respectively), indicating that enhanced AWC is favorable for the production of C2 diacid through aqueous‐phase oxidation of its higher homologous diacids, ωC2, and Gly. These results demonstrates unique reactivity of water‐soluble mineral dust particles for the enhanced production of diacids and related compounds in aqueous‐phase, having implications on the aerosol‐cloud interaction, solubility, and hygroscopicity of a dominant fraction of water‐soluble organic aerosol mass.

show abstract

“…Other important factors may be the prevalent dust and relatively high wind speed in this season. One the one hand, SOA formation in particles was likely driven by the acid-base reactions involving the acidic organics formed by photochemical reactions of VOCs and the preexisting dust (Cachier, 2005;Guinot et al, 2007;Liu et al, 2013;Wang et al, 2015a). On the other hand, high wind speed in spring was favorable for the long-range transport of aging aerosols with great proportion of WSOC/OC fractions from remote region (Salma et al, 2007).…”

Section: Temporal Variations Of Wsoc and Wsoc/oc Ratiomentioning

confidence: 99%

Water-soluble organic carbon (WSOC) and its temperature-resolved carbon fractions in atmospheric aerosols in Beijing

Tang

Zhang

Wang

et al. 2016

Atmospheric Research

View full text Add to dashboard Cite

Field observation on secondary organic aerosols during Asian dust storm periods: Formation mechanism of oxalic acid and related compounds on dust surface

Cited by 45 publications

References 57 publications

Sensitivity of transatlantic dust transport to chemical aging and related atmospheric processes

Sensitivity of transatlantic dust transport to chemical aging and related atmospheric processes

Sources and formation processes of water‐soluble dicarboxylic acids, ω‐oxocarboxylic acids, α‐dicarbonyls, and major ions in summer aerosols from eastern central India

Water-soluble organic carbon (WSOC) and its temperature-resolved carbon fractions in atmospheric aerosols in Beijing

Contact Info

Product

Resources

About