Analysis of the Co-existence of Long-range Transport Biomass Burning and Dust in the Subtropical West Pacific Region

Iron content in aerosol particles and its impact on atmospheric chemistry

Atmospheric aerosol effects on ecological and human health remain uncertain due to their highly complex and evolving nature when suspended in air. Atmospheric chemistry, global climate/oceanic and health exposure models need to incorporate more realistic representations of aerosol particles, especially their bulk and surface chemistry, to account for the evolution in aerosol physicochemical properties with time. (Photo)chemistry driven by iron (Fe) in atmospheric aerosol particles from natural and anthropogenic sources remains limited in these models, particularly under aerosol liquid water conditions. In this feature article, recent advances from our work on Fe (photo)reactivity in multicomponent aerosol systems are highlighted. More specifically, reactions of soluble Fe with aqueous extracts of biomass burning organic aerosols and proxies of humic like substances leading to brown carbon formation are presented. Some of these reactions produced nitrogen-containing gaseous and condensed phase products. For comparison, results from these bulk aqueous phase chemical studies were compared to those from heterogeneous reactions simulating atmospheric aging of Fe-containing reference materials. These materials include Arizona test dust (AZTD) and combustion fly ash particles. Also, dissolution of Fe and other trace elements is presented from simulated human exposure experiments to highlight the impact of aerosol aging on levels of trace metals. The impacts of these chemical reactions on aerosol optical, hygroscopic and morphological properties are also emphasized in light of their importance to aerosol-radiation and aerosol-cloud interactions, in addition to biogeochemical processes at the sea/ocean surface microlayer upon deposition. Future directions for laboratory studies on Fe-driven multiphase chemistry are proposed to advance knowledge and encourage collaborations for efficient utilization of expertise and resources among climate, ocean and health scientific communities.

About Validation-Comparison of Burned Area Products

This paper proposes a validation-comparison method for burned area (BA) products. The technique considers: (1) bootstrapping of scenes for validation-comparison and (2) permutation tests for validation. The research focuses on the tropical regions of Northern Hemisphere South America and Northern Hemisphere Africa and studies the accuracy of the BA products: MCD45, MCD64C5.1, MCD64C6, Fire CCI C4.1, and Fire CCI C5.0. The first and second parts consider methods based on random matrix theory for zone differentiation and multiple ancillary variables such as BA, the number of burned fragments, ecosystem type, land cover, and burned biomass. The first method studies the zone effect using bootstrapping of Riemannian, full Procrustes, and partial Procrustes distances. The second method explores the validation by using distance permutation tests under uncertainty. The results refer to Fire CCI 5.0 with the best BA description, followed by MCD64C6, MCD64C5.1, MCD45, and Fire CCI 4.1. It was also found that biomass, total BA, and the number of fragments affect the BA product accuracy.

Relationship between temporal anomalies in PM2.5 concentrations and reported influenza/influenza-like illness activity

A small number of studies suggest atmospheric particulate matter with diameters 2.5 micron and smaller (PM2.5) may possibly play a role in the transmission of influenza and influenza-like illness (ILI) symptoms. Those studies were predominantly conducted under moderately to highly polluted outdoor atmospheres. The purpose of this study was to extend the data set to include a less polluted atmospheric environment. A relationship between PM2.5 and ILI activity extended to include lightly to moderately polluted atmospheres could imply a more complicated mechanism than that suggested by existing studies. We obtained concurrent PM2.5 mass concentration data, meteorological data and reported Influenza and influenza-like illness (ILI) activity for the light to moderately polluted atmospheres over the Tucson, AZ region. We found no relation between PM2.5 mass concentration and ILI activity. There was an expected relation between ILI, activity, temperature, and relative humidity. There was a possible relation between PM2.5 mass concentration anomalies and ILI activity. These results might be due to the small dataset size and to the technological limitations of the PM measurements. Further study is recommended since it would improve the understanding of ILI transmission and thereby improve ILI activity/outbreak forecasts and transmission model accuracies.

Seasonal variation of chemical characteristics of fine particulate matter at a high-elevation subtropical forest in East Asia

The aim of this study was to chemically characterize the fine particulate matter (PM_2.5) at a subtropical forest in East Asia under the influences of anthropogenic and biogenic sources and a complex topographic setting. Four seasonal campaigns were conducted at the Xitou Experimental Forest in central Taiwan from the winter of 2013 to the autumn of 2014. The results indicated that the ambient levels and chemical features of PM_2.5 exhibited pronounced seasonal variations. Non-sea-salt sulfate (nss-SO₄^2-) constituted the major component of PM_2.5, followed by ammonium (NH₄⁺) and nitrate (NO₃^-) during winter, summer and autumn. However, it was revealed that the mass fraction of NO₃^- increased to be comparable with that of nss-SO₄^2- in springtime. The mass contribution of secondary organic carbon (SOC) to PM_2.5 peaked in summer (13.2%), inferring the importance of enhanced photo-oxidation reactions in SOC formation. Diurnal variations of O₃ and SO₂ coincided with each other, suggesting the transport of aged pollutants from distant sources, whereas CO and NO_x were shown to be under the influences of both local and regional sources. Notably high sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) were observed, which were 0.93 ± 0.05 and 0.39 ± 0.20, respectively. Precursor gases (i.e. SO₂ and NO_x) could be converted to sulfate and nitrate during the transport by the uphill winds. Furthermore, due to the high relative humidity at Xitou, enhanced aqueous-phase and/or heterogeneous reactions could further contribute to the formation of sulfate and nitrate at the site. This study demonstrated the significant transport of urban pollutants to a subtropical forest by the mountain-valley circulations as well as the long-range transport from regional sources, whereas the implications of which for regional climate change necessitated further investigation.