Evaluation of the Sources, Precursors, and Processing of Aerosols at a High-Altitude Tropical Site

Abstract

This work presents the results from a set of aerosol-and gas-phase measurements collected during the BIO-MAI ̈DO field campaign in Reúnion between March 8 and April 5, 2019. Several offline and online sampling devices were installed at the Mai ̈do Observatory (MO), a remote high-altitude site in the Southern Hemisphere, allowing the physical and chemical characterization of atmospheric aerosols and gases. The evaluation of short-lived gas-phase measurements allows us to conclude that air masses sampled during this period contained little or no anthropogenic influence. The dominance of sulfate and organic species in the submicron fraction of the aerosol is similar to that measured at other coastal sites. Carboxylic acids on PM 10 showed a significant contribution of oxalic acid, a typical tracer of aqueous processed air masses, increasing at the end of the campaign. This result agrees with the positive matrix factorization analysis of the submicron organic aerosol, where more oxidized organic aerosols (MOOAs) dominated the organic aerosol with an increasing contribution toward the end of the campaign. Using a combination of air mass trajectories (model predictions), it was possible to assess the impact of aqueous phase processing on the formation of secondary organic aerosols (SOAs). Our results show how specific chemical signatures and physical properties of air masses, possibly affected by cloud processing, can be identified at Reúnion. These changes in properties are represented by a shift in aerosol size distribution to large diameters and an increased contribution of secondary sulfate and organic aerosols after cloud processing.

Measurement Report: Bio-physicochemistry of tropical clouds at Maïdo (Réunion Island, Indian Ocean): overview of results from the BIO-MAÏDO campaign

“…A clear shift in the aerosol size distribution was observed (an increase by 15% of Aitken and accumulation mode aerosols under cloudy conditions), as well as a shift in the organic aerosol chemistry with increases in MOOA, in oxalic acid concentrations and in sulfate aerosols in the PM10 offline filters. These observations together with model estimates of in-cloud processing of aerosols suggest that oxidation of gaseous precursors, and primary organic aerosol species and other aqueous phase processing have a significant impact on the sources of organic aerosol (notably oxalic acid), and on aerosol physical properties (Dominutti et al, 2022b).…”

“…using the Time-of-Flight Aerosol chemical speciation monitor (ToF-ACSM), PM10 filter sampling using a high-volume sampler identical to those deployed at PF-1 (Dominutti et al 2022b), and by the same set of instruments deployed at DOS-2 to characterize the microphysical properties of clouds. The chemical and biological analyses of PM10 performed from filters are the same as at PF-1.…”

“…The NR-PM1 were dominated by SO4 2-(57.3%), followed by organics (23.3%), NH4 + (14.2%), and NO3 -(2.2%) (Dominutti et al, 2022b). The high concentration of sulfate containing particles and the low concentration of NH4 + , show that forms of sulfate, other than ammonium sulphate ((NH4)2SO4), were sampled, likely acidic aerosol such as NH4HSO4 or eventually in the form of organosulphates (Brito et al, 2018).…”

In Situ Observation of Multiphase Oxidation-Driven Secondary Organic Aerosol Formation during Cloud Processing at a Mountain Site in Southern China

“…Besides, isoprene can be oxidized to MO-OOA during the later stages of cloud events. 20 Our knowledge of SOA production by gas-phase chemistry has been improved considerably in recent decades, while the SOA formation in clouds is less well understood. 21,22 Therefore, more field measurements are needed to understand the aqueous-phase mechanisms and important factors that critically affect the aq-SOA formation, including oxidants (e.g., hydroxyl radicals, ozone, and nitrate radicals) in cloud droplets, sunlight, droplet pH, and particle composition.…”

“…suggested that the LV-OOA formation was dominated by photochemical oxidation processes during haze events in Hong Kong, while aqueous phase SOA (aq-SOA) by photooxidation contributes a large proportion to the daytime OOA in Beijing. , Mandariya et al indicated that hydroxylation is crucial for the formation of OA during fog activating periods, whereas oligomerization by addition of carbonyl (aldehyde/ketone) could occur during fog dissipating periods. Besides, isoprene can be oxidized to MO-OOA during the later stages of cloud events . Our knowledge of SOA production by gas-phase chemistry has been improved considerably in recent decades, while the SOA formation in clouds is less well understood. , Therefore, more field measurements are needed to understand the aqueous-phase mechanisms and important factors that critically affect the aq-SOA formation, including oxidants (e.g., hydroxyl radicals, ozone, and nitrate radicals) in cloud droplets, sunlight, droplet pH, and particle composition …”