Abstract Fire plumes are rising columns of heated air masses, consisting of gaseous and particulate matter generated by combustion, affecting air quality, climate and public health. The chemical species released undergo secondary reactions and participate in chemical and physical interactions, altering the properties of the fire plume. The ability of the plume to be transported across short and long distances, depending on the atmospheric conditions, reveals the high importance of unraveling the chemical pathways influencing its inner and outer pollutants. Fresh plumes, close to the fire source, typically exhibit high temperatures and rapid reactions. In contrast, aged plumes differ in composition due to shifts in chemical regimes. The presence of sunlight influences oxidative reactions, while its absence favors oxidation paths driven by NO x chemistry. The complexity of fire plume chemistry presents challenges in efficient characterization of species formation and decomposition. It also directly influences gas‐phase species chemical pathways, in‐plume evolution and formation of secondary air pollutants, as well as particulate matter composition and fate. This review provides a detailed description of the chemical mechanisms and pathways inside fresh and aged fire plumes and discusses the implications of critical parameters influencing plume composition. Main tracers are identified, and key processes are described, with information reviewed from laboratory, field, and satellite studies. Unaddressed aspects and emerging opportunities are discussed to provide potential future directions of investigation.
Abstract Concerted exploration and a ten‐fold increase in Martian meteorites reveal a mostly ancient (>4 Ga), lithologically diverse mafic crust (igneous SiO 2 ranging from ∼40%–70%), commonly exhibiting alkaline affinities and with felsic compositions restricted to ancient crust. Most crustal growth (∼80%) took place during the pre‐Noachian, resulting from magma ocean processes. Later crustal additions continued at diminishing rates to the latest Amazonian (<200 Ma). Data from the first fully operational seismometer (InSight mission) indicate the crust is 49 7 km thick on average (∼4 1% of the primitive mantle), with an intracrustal discontinuity, of possible global extent, at about 20–30 km depth. InSight results also suggest a ∼150 km‐thick molten silicate layer (MSL) at the base of the mantle, a possible remnant of the early magma ocean. The MSL represents a distinctive, incompatible (including heat producing) element‐enriched geochemical reservoir, comparable in physical size to the crust. A model for Martian crustal composition indicates a mildly incompatible and heat‐producing element‐enriched basaltic composition (e.g., SiO 2 = 48%, K 2 O = 0.5%, La N /Yb N ∼ 1.8) that becomes less incompatible element‐enriched over geological time. The petrological nature of the crust likely varies in a complex way with depth that may explain the intracrustal seismic discontinuity. The crust contains ∼45 10% of the most incompatible elements in the primitive mantle and this composition is consistent with a mass balance model among crust, MSL, “depleted” mantle and primitive mantle. A geodynamic model for Mars can be constructed that is consistent with geophysical and geochemical constraints currently available.
Abstract River sand and gravel are mined worldwide at volumes that now rival their natural replenishment, yet quantitative knowledge of this mining activity and its consequences lags far behind many other global environmental pressures. We synthesize 411 peer‐reviewed studies published since 1974 within a new Driver‐to‐Management Pathway for Sustainable Sand and Gravel Mining framework that links socio‐economic demand, spatial‐temporal extent of extraction, hydrogeomorphic change, socio‐ecological disruption, and management response. Evidence shows a pronounced scale mismatch: regional‐to‐global drivers fuel largely unreported local extraction, while impacts propagate well beyond mining sites. In most documented cases, annual removal exceeds bed‐material supply several‐fold, producing channel incision, bank collapse, declining groundwater tables, deteriorating water quality, and inland migration of saline water in coastal areas. These physical changes cascade into habitat loss, infrastructure damage, and livelihood insecurity, especially across rapidly developing regions of Asia and Africa. Despite the proliferation of impact studies (69% of the literature), research is dominated by hydrogeomorphic perspectives, with ecological and socio‐economic impacts far more often treated as secondary or co‐occurring components rather than primary foci; meanwhile, only 27% of studies quantify extraction extent and 24% analyze demand drivers, hampering the design of effective interventions. Together, these findings highlight the need for basin‐scale monitoring, cross‐boundary governance, and demand‐side interventions that explicitly link extraction limits to sediment budgets.
Abstract The lightning return stroke is the most impactful aspect of a lightning flash. It has a transformative effect on the Earth system by igniting wildfires and by fixing nitrogen oxides in the atmosphere. It also has important detrimental impacts on societal infrastructure by causing billions of dollars in losses every year to power transmission and communications industries. The impacts of a lightning return stroke are due to its intense electrical current, which surges when lightning channels connect to a ground structure, and travels rapidly through those channels toward the cloud. The intense energy deposition in the atmosphere results in emissions across the entire electromagnetic spectrum. In this work, we present an overview on how to calculate the lightning return stroke electrical current using the Telegrapher's Equations, which describe the propagation of electrical signals guided by a conductor. This article has three main goals. First, it presents a tutorial overview on how to assemble a basic model of the lightning return stroke. Second, the article explains from basic principles the dominant features of the current wave, including: the genesis of channel‐base current, and the subsequent propagation, attenuation, and dispersion. Third, it also serves as a literature review by drawing parallels between the return stroke properties inferred from the Telegrapher's Equations and those established in previous theoretical and experimental research.
Abstract Propagating waves on the ocean surface can be represented as a stochastic process whose statistics are characterized by a spectrum. This paper reviews methods for measuring the wave spectrum and related quantities. Observations begin by sensing fluid dynamical properties of the sea surface over space and/or time. Visual observations, collected routinely since the mid‐18th century, comprise the longest‐running wave record. Nearshore measurement methods continue to advance, including traditional pressure and acoustic sensing as well as newer technologies like distributed acoustic sensing and LiDAR. Detailed small‐scale wave physics can now be explored with measurement techniques using light, including stereo‐imaging and polarimetry. Reductions in the size, cost, and power consumption of microelectronics have propagated through ocean wave instrumentation, most notably in wave buoys. Global networks of freely drifting miniature wave buoys offer novel observational capabilities. Remote sensing techniques based on radar and LiDAR continue to evolve and are widely deployed from land, ships, aircraft, autonomous vehicles, and satellites. Spaceborne altimeters form one of the most important records of wave height, and new spaceborne sensors now observe directional spectra globally with sampling akin to traditional altimetry. Aircraft and autonomous systems provide strategic sampling capabilities for detailed process studies and access to extreme storm environments. The quality and quantity of ocean wave measurements have never been greater. This review aims to help make sense of it all.
