Dear Colleagues,

There are at least three principal lines of inquiry to consider in a special issue of Atmosphere devoted to airborne particulates:

(1) Elevated [PM₁₀] of crustal particles suspended by high winds over arid or semi-arid regions, whose sources are both natural and anthropogenic, and whose human health effects could be reduced by better forecasting methods. Numerical simulation models for this type of [PM₁₀] need to be improved, especially, but not limited to, the dust emission models that have to be coupled with the physical transport models to enable such simulations;

(2) Elevated [PM_2.5], also known as fine particles, in which a better understanding of their chemical composition and of their atmospheric dispersion could lead to more effective forecasting and more definitive source attributions. These fine particle concentrations are much easier to simulate than the size fraction of [PM₁₀]; nonetheless, improvements could still be forthcoming, especially with regard to their chemical composition and to their effects on visibility degradation. Of special concern are the carbonaceous fine particles -- elemental carbon, organic carbon, brown carbon -- because they are so ubiquitous and because they pose threats to human health, to visibility, and through their deposition, to the general ecosystem; and

(3) Already peer-reviewed journals have published research into how the pandemic-induced reduction of vehicular traffic and other economic activities have affected air quality. This research has examined air pollutant concentrations for both gaseous and particulates species.  As the pandemic persists but weakens (let us hope), this kind of research should be encouraged.

The special issue, if it comes together toward the latter part of this calendar year or early in the next, would then be able to publish research articles on this topic that are based on several months of activity reductions and of ground-based or satellite-based particulates measurements. Thus far, substantial reductions of [PM_2.5] and [NO₂] but in some cases increases in [O₃] have been observed. In many regions (but by no means all) fine particulates concentrations tend to highest in the colder months. The higher the concentrations, the easier it is to measure and model them; suggesting that the winter [PM_2.5] of 2020 – 2021 could then be analyzed, but because of typical delays in laboratory analyses, could not be interpreted and written up until mid-2021.

Subject areas may include, but are not limited to:

• Carbonaceous particulates, their emission sources, their monitoring, their morphology, their health effects,
• Chemical composition of [PM₅] with emphasis on visibility degradation,
• Chemical composition of [PM₅], with emphasis on those elements and compounds with demonstrable adverse health effects,
• [PM₁₀] in arid or semi-arid climates: emission sources both natural and anthropogenic, with some research on the resultant concentrations,
• Numerical simulations of [PM₁₀] and/or [PM₅] in urban airsheds, and
• Deposition of airborne particulates over fairly long distances and how such deposition affects the ecosystems to which they are transported.

Although barely mentioned above, research on novel monitoring methods and on new analytical laboratory procedures that quantify and speciate airborne particulates is always important.  Papers about this aspect of airborne particulates are most naturally welcome.  Just two of the above six topics mention emissions, but quantifying emissions is critical for understanding their resultant concentrations and for ultimately devising and carrying out emission reduction strategies to reduce them.  Research on particulates emissions, then, would most assuredly fit into this special issue.

Dr. Peter Hyde
Guest Editor

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• air quality
• particulate matter
• numerical simulation models
• chemical composition
• human health