[1] Particle number concentration in the troposphere is an important parameter controlling the climate and health impacts of atmospheric aerosols. We show that nucleation rates and total particle number concentrations in the troposphere, predicted by different nucleation schemes, differ significantly. Our extensive comparisons of simulated results with land-, ship-, and aircraft-based measurements indicate that, among six widely used nucleation schemes involving sulfuric acid, only the ion-mediated nucleation (IMN) scheme can reasonably account for both absolute values (within a factor of ∼2) and spatial distributions of particle number concentrations in the whole troposphere. Binary homogeneous nucleation (BHN) schemes significantly underpredict particle number concentration in the lower troposphere (below ∼500 mbar), especially in the boundary layer over major continents (by a factor of up to ∼10). BHN is also insignificant in the upper troposphere based on a recent kinetically self-consistent nucleation model constrained by multiple independent laboratory data. Previous conclusions about the importance of BHN in the upper troposphere should be revisited. Empirical activation and kinetic nucleation formulas significantly overpredict the particle number concentrations over tropical and subtropical oceans (by a factor of up to ∼10 in the boundary layer), and the overpredictions extend from ocean surface to around ∼400 mbar. This study represents the first comprehensive comparison of global particle number simulations with relevant measurements that have a 3-D global spatial coverage. Our results suggest that ion-mediated H 2 SO 4 -H 2 O nucleation appears to dominate over neutral H 2 SO 4 -H 2 O nucleation, not only in the lower troposphere but also in the middle and upper troposphere.

The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) is an interdisciplinary investigation to improve understanding of Earth's ocean ecosystem-aerosol-cloud system. Specific overarching science objectives for NAAMES are to (1) characterize plankton ecosystem properties during primary phases of the annual cycle and their dependence on environmental forcings, (2) determine how these phases interact to recreate each year the conditions for an annual plankton bloom, and (3) resolve how remote marine aerosols and boundary layer clouds are influenced by plankton ecosystems. Four NAAMES field campaigns were conducted in the western subarctic Atlantic between November 2015 and April 2018, with each campaign targeting specific Behrenfeld et al. NAAMES Overview seasonal events in the annual plankton cycle. A broad diversity of measurements were collected during each campaign, including ship, aircraft, autonomous float and drifter, and satellite observations. Here, we present an overview of NAAMES science motives, experimental design, and measurements. We then briefly describe conditions and accomplishments during each of the four field campaigns and provide information on how to access NAAMES data. The intent of this manuscript is to familiarize the broad scientific community with NAAMES and to provide a common reference overview of the project for upcoming publications.

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The concept of coevolution was first developed by Darwin, who used it to explain how pollinators and food-rewarding flowers involved in specialized mutualisms could, over time, develop long tongues and deep tubes, respectively. He famously predicted that Angraecum sesquipedale, a long-spurred Malagasy orchid, must be pollinated by a hawkmoth with an exceptionally long tongue. Darwin's idea of a coevolutionary "race" was championed by contemporary naturalists, including Alfred Wallace, and a hawkmoth fitting the expected tonguelength profile was eventually discovered in Madagascar during the early twentieth century. However, strong empirical support for the mechanism behind Darwin's coevolutionary model has been forthcoming only in the past two decades. It is now established that selection often strongly favors plants with floral tubes that exceed the length of their pollinator's tongues. There is also evidence that pollinators gain an energetic benefit from having tongues that enable them to consume most or all of the nectar in deep tubular flowers. Alternative explanations for the evolution of long pollinator tongues, such as evasion of predators that use flowers as ambush sites, are considered much less compelling and lack quantitative support. Another important advance in coevolution research has been the development of approaches that explicitly predict a geographical mosaic of coevolution. The expectation that coevolution can lead to geographical diversification and trait covariation among strongly interacting organisms is strongly supported by studies of long-proboscid fly and oilbee pollination systems in South Africa. Macro-and microevolutionary studies of pollination systems suggest that coevolution can operate alongside other one-sided evolutionary processes, such as shifts, in shaping plant and pollinator traits.

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