Roland von Glasow

Atmospheric Chemistry of Iodine

Atmospheric Chemistry of Iodine Alfonso Saiz-Lopez,* John M. C. Plane,* Alex R. Baker, Lucy J. Carpenter, Roland von Glasow, Juan C. G omez Martín, Gordon McFiggans, and Russell W. Saunders Laboratory for Atmospheric and Climate Science (CIAC), CSIC, Toledo, Spain School of Chemistry, University of Leeds, Leeds, LS2 9JT, United Kingdom School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom School of Earth, Atmospheric & Environmental Sciences, University of Manchester, Manchester, M13 9PL, United Kingdom

Tropospheric Halogen Chemistry:Sources, Cycling, and Impacts

In the past 40 years, atmospheric chemists have come to realize that halogens exert a powerful influence on the chemical composition of the troposphere and through that influence affect the fate of pollutants and may affect climate. Of particular note for climate is that halogen cycles affect methane, ozone, and particles, all of which are powerful climate forcing agents through direct and indirect radiative effects. This influencecomes from the high reactivity of atomic halogen radicals (e.g.,Cl, Br, I) and halogen oxides (e.g., ClO, BrO, IO, and higher oxides), known as reactive halogen species in this review. These reactive halogens are potent oxidizers for organic and inorganic compounds throughout the troposphere.

Variation of sea salt aerosol pH with relative humidity

Calculations of the pH of sea salt aerosol particles show that the pH decreases with increasing relative humidity and therefore increasing liquid water content of the particles. We show that this puzzling effect is a result of the high concentration of chloride in the particles and the phase partitioning of HCl between the gas and aqueous phase, that makes the gas phase act as a reservoir for acidity for the sea salt particles. Implications for the marine boundary layer are briefly discussed.

Megacities and Large Urban Agglomerations in the Coastal Zone: Interactions Between Atmosphere, Land, and Marine Ecosystems

Megacities are not only important drivers for socio-economic development but also sources of environmental challenges. Many megacities and large urban agglomerations are located in the coastal zone where land, atmosphere, and ocean meet, posing multiple environmental challenges which we consider here. The atmospheric flow around megacities is complicated by urban heat island effects and topographic flows and sea breezes and influences air pollution and human health. The outflow of polluted air over the ocean perturbs biogeochemical processes. Contaminant inputs can damage downstream coastal zone ecosystem function and resources including fisheries, induce harmful algal blooms and feedback to the atmosphere via marine emissions. The scale of influence of megacities in the coastal zone is hundreds to thousands of kilometers in the atmosphere and tens to hundreds of kilometers in the ocean. We list research needs to further our understanding of coastal megacities with the ultimate aim to improve their environmental management.

Interaction of radiation fog with tall vegetation

Abstract A one-dimensional radiation fog model is presented. It is coupled with a second model to include the effects of tall vegetation. The fog model describes in detail the dynamics, thermodynamics, and microphysical structure of a fog, as well as the interactions with the atmospheric radiative transfer. A two-dimensional joint size distribution for the aerosol particles and activated fog droplets is used, the activation of aerosol particles is explicitly modeled. The implications of the presence of tall vegetation on the state of the atmosphere and on the evolution of radiation fog are stated. It is shown that the existence of tall vegetation impedes the evolution of radiation fog. The life cycle of radiation fog is discussed. The input of fog water and associated aerosol particles onto the vegetation surfaces via fog water interception processes is assessed.

Multiphase halogen chemistry in the tropical Atlantic Ocean.

We used a one-dimensional model to simulate the chemical evolution of air masses in the tropical Atlantic Ocean, with a focus on halogen chemistry. The model results were compared to the observations of inorganic halogen species made in this region. The model could largely reproduce the measurements of most chlorine species, especially under unpolluted conditions, but overestimated sea salt chloride, BrCl, and bromine species. Agreement with the measurements could be improved by taking into account the reactivity with aldehydes and the effects of dimethyl sulfide (DMS) and Saharan dust on aerosol pH; a hypothetical HOX → X(-) aqueous-phase reaction could also improve the agreement with measured Cl(2) and HOCl, especially under semipolluted conditions. The results also showed that halogens speciation and concentrations are very sensitive to cloud processing. The model was used to calculate the impact of the observed levels of halogens: Cl atoms accounted for 5.4-11.6% of total methane sinks and halogens (mostly bromine and iodine) accounted for 35-40% of total ozone destruction.

Atmospheric chemistry: sun, sea and ozone destruction.

Halogens are known to decrease the levels of stratospheric ozone. The latest measurements show that something similar occurs in the lower atmosphere over tropical oceans — and probably above most other oceans, too. Tropospheric ozone is an important greenhouse gas in addition to its influence on air quality, on the photochemical processing of atmospheric chemicals and on ecosystem viability. Increasing tropospheric ozone levels over the past 150 years have led to a significant climate perturbation and a full understanding of the factors controlling the tropospheric ozone budget is required. The tropical marine boundary layer is the most important global region for loss of ozone, because of its high water vapour content, high solar radiation levels and large geographical extent. Surface atmospheric observations in this region are extremely sparse, hence the importance of a new year-round dataset from Cape Verde Observatory in the tropical North Atlantic Ocean. The observations reveal that the photochemical destruction rate of ozone in the tropical marine boundary layer is about 50% greater than predicted by current global models, and that this destruction is caused by halogen chemistry.

Evolving research directions in Surface Ocean–Lower Atmosphere (SOLAS) science

This review focuses on critical issues in ocean-atmosphere exchange that will be addressed by new research strategies developed by the international Surface Ocean-Lower Atmosphere Study (SOLAS) research community. Eastern boundary upwelling systems are important sites for CO2 and trace gas emission to the atmosphere, and the proposed research will examine how heterotrophic processes in the underlying oxygen-deficient waters interact with the climate system. The second regional research focus will examine the role of sea-ice biogeochemistry and its interaction withatmosphericchemistry.Marineaerosolsarethefocusofaresearchthemedirectedatunderstandingtheprocessesthat determine their abundance, chemistry and radiative properties. A further area of aerosol-related research examines atmospheric nutrient deposition in the surface ocean, and how differences in origin, atmospheric processing and composition influence surface ocean biogeochemistry. Ship emissions are an increasing source of aerosols, nutrients and toxins to the atmosphere and ocean surface, and an emerging area of research will examine their effect on ocean biogeochemistry and atmospheric chemistry. The primary role of SOLAS is to coordinate coupled multi-disciplinary research withinresearch strategies thataddresstheseissues, toachieverobust representationofcritical ocean-atmosphere exchange processes in Earth System models.

Atmospheric chemistry: Wider role for airborne chlorine

Unexpected chlorine chemistry in the lowest part of the atmosphere can affect the cycling of nitrogen oxides and the production of ozone, and reduce the lifetime of the greenhouse gas methane.

A look at the CLAW hypothesis from an atmospheric chemistry point of view

Environmental context. Feedbacks in the climate system as suggested by, for example, the CLAW hypothesis have often been accepted as fact whereas many open questions remain. In this manuscript some of these uncertainties and their implications are discussed and additional processes that might drastically change the importance of this suggested feedback loop are highlighted.