Processing of aerosol particles within the Habshan pollution plume

Abstract

The Habshan industrial site in the United Arab Emirates produces a regional-scale pollution plume associated with oil and gas processing, discharging high loadings of sulfates and chlorides into the atmosphere, which interact with the ambient aerosol population. Aerosol particles and trace gas chemistry at this site were studied on two flights in the summer of 2002. Measurements were collected along vertical plume profiles to show changes associated with atmospheric processing of particle and gas components. Close to the outlet stack, particle concentrations were over 10,000 cm À3 , dropping to <2000 cm À3 in more dilute plume around 1500 m above the stack. Particles collected close to the stack and within the dilute plume were individually measured for size, morphology, composition, and mixing state using transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy. Close to the stack, most coarse particles consisted of mineral dust and NaCl crystals from burning oil brines, while sulfate droplets dominated the fine mode. In more dilute plume, at least 1500 m above the stack, the particle spectrum was more diverse, with a significant increase in internally mixed particle types. Dilute plume samples consisted of coarse NaCl/silicate aggregates or NaCl-rich droplets, often with a sulfate component, while fine-fraction particles were of mixed cation sulfates, also internally mixed with nanospherical soot or silicates. Thus, both chloride and sulfate components of the pollution plume rapidly reacted with ambient mineral dust to form coated and aggregate particles, enhancing particle size, hygroscopicity, and reactivity of the coarse mode. The fine-fraction sulfate-bearing particles formed in the plume contribute to regional transport of sulfates, while coarse sulfate-bearing fractions locally reduced the SO 2 loading through sedimentation. The chloride-and sulfate-bearing internally mixed particles formed in the plume markedly changed the reflectivity and scattering properties of the ambient aerosol population, as well as its hygroscopic and ice nucleation properties.

Analysis of aerosol-cloud interactions and their implications for precipitation formation using aircraft observations over the United Arab Emirates

“…Alternatively, higher tail concentrations from ultra-giant sizes of 20-50 µm are recorded during SF4 compared with SF1. This is in line with the previous suggestion of higher ultra-giant CCN loading from local pollution and dust aggregation over the southwest compared with the eastern regime (Semeniuk et al, 2015).…”

“…Furthermore, the ambient aerosols appear to be naturally hygroscopic as suggested by their deliquescence and growth to sizes of ∼ 7 µm (peak concentrations) at cloud base. This is more pronounced over the southwestern region where mineral aggregates are formed from sea salt and sulfate particles emitted from local oil refineries (Semeniuk et al, 2015). While the C-C process remained inactive in all observed cases, it is hypothesized that the presence of large dust and pollution aggregates causes a "natural competition effect" as reported by Tessendorf et al (2021) based on their aircraft observations from the Queensland Cloud Seeding Research Program (QCSRP).…”

“…Laboratory deliquescence experiments show that pure insoluble mineral dust particles remain hydrophobic at 100 % relative humidity (RH), whereas the aggregation of dust particles with soluble compounds (e.g., NaCl) results in their deliquesce at 74 % RH (Wise et al, 2007). Similarly, compounds from anthropogenic pollution (sulfates) interact with mineral dust to produce internally mixed aggregates that deliquesce at 80 % RH (Semeniuk et al, 2015).…”

A conceptual framework for mixing structures in individual aerosol particles

“…Based on the results from different sampling sites, dispersed‐OM and dumbbell structures are not common mixing structures (Figure ) and tend to transform into OM‐coating and core‐shell structures (Figure ). We conclude that OM‐coating and core‐shell structures are important indicators of particle aging in clean and polluted air (Figure ), except when close to the specific emission sources [ Semeniuk et al ., ].…”

“…Based on the results from different sampling sites, dispersed-OM and dumbbell structures are not common mixing structures ( Figure 6) and tend to transform into OM-coating and core-shell structures (Figure 8). We conclude that OM-coating and core-shell structures are important indicators of particle aging in clean and polluted air ( Figure 6), except when close to the specific emission sources [Semeniuk et al, 2015]. Bauer et al [2013] suggested that the knowledge of realistic mixing structures of individual particles is necessary to explain their hygroscopicity, cloud condensation nucleus activity, and optical properties in field measurements and modeling simulations.…”