Role of the stratosphere in the global mercury cycle.

Mercury (Hg) is a global pollutant with substantial risks to human and ecosystem health. By upward transport in tropical regions, mercury enters into the stratosphere, but the contribution of the stratosphere to global mercury dispersion and deposition remains unknown. We find that between 5 and 50% (passing through the 400-kelvin isentropic surface and tropopause, respectively) of the mercury mass deposited on Earth's surface is chemically processed in the lower stratosphere.

Kinetics of O with Ca and Its Higher Oxides CaO ( = 1-3) and Updates to a Model of Meteoric Calcium in the Mesosphere and Lower Thermosphere.

The room-temperature rate constants and product branching fractions of CaO ( = 0-3) + O are measured using a selected ion flow tube apparatus. Ca + O produces CaO + O with = 9 ± 4 × 10 cm s, within uncertainty equal to the Langevin capture rate constant. This value is significantly larger than several literature values.

The Chemistry of Mercury in the Stratosphere.

Mercury, a global contaminant, enters the stratosphere through convective uplift, but its chemical cycling in the stratosphere is unknown. We report the first model of stratospheric mercury chemistry based on a novel photosensitized oxidation mechanism. We find two very distinct Hg chemical regimes in the stratosphere: in the upper stratosphere, above the ozone maximum concentration, Hg oxidation is initiated by photosensitized reactions, followed by second-step chlorine chemistry.

Ambient PM and Related Health Impacts of Spontaneous Combustion of Coal and Coal Gangue.

Coal and coal gangue spontaneous combustion (CGSC) occurs globally, causing significant environmental pollution. However, its emissions are poorly quantified and are overlooked in global or regional air pollutant emission inventories in previous studies, resulting in the underestimation of its impacts on climate, environment, and public health. This study quantified the emissions of various air pollutants originating from CGSC in Wuhai, a city in China, investigated emission characteristics, and estimated the contribution of CGSC emissions to fine particulate matter (PM) air pollution and related health impacts on a regional scale.

Water Photolysis and Its Contributions to the Hydroxyl Dayglow Emissions in the Atmospheres of Earth and Mars.

Airglow is a well-known phenomenon in the Earth's upper atmosphere, which arises from the emissions of energetic atoms and molecules. The Meinel band emission from high vibrationally excited OH(X) radicals is one of the more important contributors to the airglow from the mesosphere/lower thermosphere. The H + O reaction has long been regarded as the dominant source of these OH(X, high ) radicals.

Silicon chemistry in the mesosphere and lower thermosphere.

Silicon is one of the most abundant elements in cosmic dust, and meteoric ablation injects a significant amount of Si into the atmosphere above 80 km. In this study, a new model for silicon chemistry in the mesosphere/lower thermosphere is described, based on recent laboratory kinetic studies of Si, SiO, SiO, and Si. Electronic structure calculations and statistical rate theory are used to show that the likely fate of SiO is a two-step hydration to silicic acid (Si(OH)), which then polymerizes with metal oxides and hydroxides to form meteoric smoke particles.

Mesospheric removal of very long-lived greenhouse gases SF6 and CFC-115 by metal reactions, Lyman-α photolysis, and electron attachment.

The fluorinated gases SF6 and C2F5Cl (CFC-115) are chemically inert with atmospheric lifetimes of many centuries which, combined with their strong absorption of IR radiation, results in unusually high global warming potentials. Very long lifetimes imply that mesospheric sinks could make important contributions to their atmospheric removal. In order to investigate this, the photolysis cross sections at the prominent solar Lyman-α emission line (121.

Experimental study of the mesospheric removal of NF3 by neutral meteoric metals and Lyman-α radiation.

NF3 is a potent anthropogenic greenhouse gas with increasing industrial usage. It is characterized by a large global warming potential due in part to its large atmospheric lifetime. The estimated lifetime of about 550 years means that potential mesospheric destruction processes of NF3 should also be considered.