Aerosols and Climate

Description

The ever-diversifying field of aerosol effects on climate is comprehensively presented here, describing the strong connection between fundamental research and model applications in a way that will allow both experienced researchers and those new to the field to gain an understanding of a wide range of topics. The material is consistently presented at three levels for each topic: (i) an accessible "quick read" of the essentials, (ii) a more detailed description, and (iii) a section dedicated to how the processes are handled in models. The modelling section in each chapter summarizes the current level of knowledge and what the gaps in this understanding mean for the effects of aerosols on climate, enabling readers to quickly understand how new research fits into established knowledge. Definitions, case studies, reference data, and examples are included throughout. Aerosols and Climate is a vital resource for graduate students, postdoctoral researchers, senior researchers, and lecturers in departments of atmospheric science, meteorology, engineering, and environment. It will also be of interest to those working in operational centers and policy-facing organizations, providing strong reference material on the current state of knowledge. Aerosols and Climate Copyright Symbols Contributors Acknowledgments Acronyms and abbreviations Introduction What is aerosol and why is it important for climate? Aims and scope of the book Terminology, symbols, and units References Aerosol in the climate system The historical development of our understanding of aerosol effects on climate Evidence for the effects of aerosol on climate Energy balance of the climate system Energy flows and the effects of aerosol Perturbation of energy flows Radiative forcing and subsequent atmospheric adjustments Radiative forcing agents Radiative forcing and climate response Aerosol radiative forcing Effects of aerosol on atmospheric radiation Definition of aerosol radiative forcing and its components The magnitude and distribution of aerosol radiative forcing The magnitude of aerosol radiative forcing The distribution of aerosol radiative forcing Climate response to changes in aerosol Aerosol forcing efficacy Spatial patterns of climate response Effects on the hydrological cycle and precipitation References Aerosol in the Earth system Introduction to land and ocean productivity and biogeochemistry Land productivity and biogeochemistry Human impacts on land productivity and biogeochemistry Ocean productivity and biogeochemistry Controls on ocean productivity Human impacts on ocean productivity Aerosol effects on land and ocean biogeochemistry Aerosol deposition effects on terrestrial ecosystems Aerosol deposition effects on ocean ecosystems Aerosol deposition effects on freshwater aquatic ecosystems Effects of aerosol physical climate changes on land and ocean biogeochemistry Aerosol sources and deposition to the land and oceans Reactive nitrogen sources and deposition to the land and oceans Iron sources and deposition to the oceans Phosphorus sources and deposition to the land and ocean Other aerosols and their sources and deposition Effects of climate change and land use on natural aerosol emissions Dimethyl sulfide emissions under climate change (CLAW hypothesis) Desert dust changes across the anthropocene Wildfire and open fire changes across the anthropocene Soil nitrogen precursor emissions Biogenic volatile organic compounds and particulate emissions from vegetation Sea spray responses to climate change Modeling Status of aerosol-biogeochemistry-climate feedbacks in Earth system models Magnitude of aerosol biogeochemistry feedbacks on the carbon cycle Magnitude of climate-driven natural aerosol feedbacks Acknowledgment References Global aerosol properties The aerosol particle size distribution Definition of particle size distributions Climate-relevant particles The global distribution of aerosol particles Aerosol transport pathways Spatial distribution of particle mass and number Particle chemical composition Spatial variations in the particle size distribution Small-scale aerosol variability Global distribution of aerosol precursor gases Aerosol in the preindustrial atmosphere References Aerosol processes Particle sources, sinks, and lifetime In-air processes Emission and formation of aerosol precursor gases Gas-phase formation of precursor gases Formation of secondary material within particles New particle formation (nucleation) Particle growth by vapor condensation Coagulation Dissolution Water uptake (hygroscopicity) Particle ageing Ice-nucleating particles The behavior of charged particles Removal of particles by sedimentation and dry deposition In-cloud processes and aerosol wet removal Cloud droplet formation Cloud processing and aqueous-phase chemistry Vertical transport of gases and aerosol particles in clouds (venting) Wet removal of particles and gases Summary of timescales Knowledge gaps, future challenges, and research directions References Aerosol-climate modeling Historical development of aerosol-climate modeling Pre-IPCC research contributions to aerosol-climate modeling Modeling for climate assessments: The IPCC period The range of models used in aerosol-climate research The anatomy of an atmospheric model Processes and parameterizations Parameterization essentials The concept of splitting to make calculations tractable and efficient Representation of clouds and precipitation Clouds as subgrid components of atmospheric models Representations of cloud particles Warm cloud bulk microphysics Microphysical extensions for ice treatment Representation of aerosol The aerosol particle size distribution Aerosol microphysical processes Representation of cloud-aerosol interactions Aerosol activation Aerosol removal and processing by clouds Ice- and mixed-phase cloud processes Representation of radiation interactions with clouds and aerosol Modeling considerations Model applications and evaluation Knowledge gaps, future challenges, and research directions References Historical changes in aerosol Timescales Glacial-interglacial cycles From medieval to preindustrial times Preindustrial to present day Recent decades: The aerosol instrumental period Measurements of historical changes Ice core proxy records Formation of ice archives Sampling and analyzing ice archives Ice core chronologies Interpreting aerosol ice core records Peat bog, lake and ocean sediment proxy records Peat bog records Lake and ocean sediments Deposition and surface in situ aerosol measurements Visibility, radiation, and optical properties Other methods Historical changes in aerosol Volcanoes (1000-present day) Natural and anthropogenic aerosols over the industrial period (1750-present day) Surface radiation and visibility at the Earths surface (1940-present day) The aerosol instrumental record (1990-present-day) Modeling Set-up of historical model simulations Model-simulated radiative forcing Knowledge gaps, challenges, and research directions References Aerosol and precursor gas emissions Developing emission inventories Emissions from industrial activity History of development Activity data Emission processes and emitted sizes of primary particles Emission factors Types of industrial sources Global industrial emission totals Emissions from the natural world Terrestrial sources Forests and vegetation Fires Arid environments: Dust from deserts and soils Volcanoes Marine sources Estimating past emissions Past industrial emissions Past natural emissions Future projections of emissions Economic and social scenarios Future projections of industrial emissions Future projections of natural emissions Modeling Assumptions Observational evaluation of emissions Knowledge gaps, future challenges, and research directions References Measurements of ambient aerosol properties Measurement principles and instruments Units and particle diameter definitions Concentration units Definitions of particle diameter Size distributions Uncertainties, limits of detection, and time resolution Measuring the mass, number, and size of particles Gravimetric and equivalents Optical particle detection Condensation particle counters Particle size classifiers Measuring chemical composition Soluble ions Mineral dust Carbonaceous components Bio-particles Aerosol mass spectrometry Measuring new particle formation Measuring aerosol particle optical properties Measuring water interactions Conducting ambient measurements Sampling points and inlets Sampling lines and losses Measurement platforms Data from in situ measurements Processing, file formats, and metadata Aerosol databases GAW World Data Centre for Aerosols NOAA ESRL Federated Aerosol Network IMPROVE EMEP ACTRIS IAGOS GASSP Modeling Sources of error when comparing models and measurements Sub-grid-scale variability Measurement data sparsity in space and time Case studies Evaluation of global simulations of CCN and implications for cloud droplet formation (Fanourgakis et al. 2019) Aerosol mass spectrometer constraint on the global secondary organic aerosol budget (Spracklen et al., 2011) In situ constraints on the vertical distribution of global aerosol (Watson-Parris et al., 2019) The vertical profile of organic aerosol (Heald et al., 2011) References Remote sensing measurements of aerosol properties Introduction to ultraviolet, visible, and near-infrared aerosol measurements from satellite Historical development of space-based aerosol remote sensing Early history The 1990s The EOS era Uses, strengths, and limitations of space-based aerosol remote sensing The uses of space-based aerosol remote sensing What remote sensing can and cannot tell us about aerosol Spatial and temporal coverage: Orbits and swaths Retrieval techniques Broad-swath, VNIR imager aerosol retrievals Visible-near-infrared (VNIR) multi-angle imager aerosol retrievals VNIR limb sounding aerosol retrievals UV imager aerosol retrievals Thermal infrared (TIR) sounder aerosol retrievals Active sensor aerosol retrievals Optimal estimation aerosol retrievals Remote sensing product uncertainty estimates and validation Statistical and case-study validation approaches Formal uncertainty estimates Modeling Remote sensing information commonly used to constrain models Challenges with comparing model output to remote sensing products Remote sensing in reanalyses References Aerosol-radiation interactions Fundamental aspects of aerosol interactions with radiation Radiation Scattering Scattering regimes Scattering cross section and efficiency factor Phase function, asymmetry factor, and upscatter fraction Absorption Absorption cross section and efficiency factor Extinction Optical depth Single-scattering albedo Emission Aerosol and radiative transfer Factors determining the radiative effect of aerosol-radiation interactions Optical properties of aerosol particle types Solar zenith angle Underlying surfaces Influence of clouds Atmospheric temperature and humidity profiles Rapid adjustments to radiative effects Radiative effect of aerosol-radiation interactions Radiative effect efficiency of aerosol types Aerosol radiative effect in cloud-free conditions Aerosol radiative effect in cloudy conditions Aerosol-radiative effect in all-sky conditions Radiative forcing and effective radiative forcing of aerosol-radiation interactions Simplified expressions for radiative forcing Industrial-period changes in aerosol radiative properties Industrial-period aerosol radiative forcing Effective radiative forcing Uncertainty in aerosol-radiation interactions Aerosol radiative effect Aerosol radiative forcing Modeling Dependence on aerosol representations Dependence on approximations used in radiative transfer Model evaluation References Aerosol-cloud interactions in liquid clouds Fundamental aspects of clouds and radiation The global distribution and bulk properties of clouds Cloud regimes Cloud bulk properties Effect of clouds on solar radiation Cloud reflectivity The dependence of solar radiation on cloud properties Planetary albedo Effect of clouds on terrestrial radiation The dependence of longwave radiation on cloud properties Cloud adjustments Fundamental aspects of aerosol interactions with clouds Cloud sources Turbulence, vertical motion, and adiabatic cooling Droplet activation Condensational growth and supersaturation Cloud sinks Precipitation formation via warm-rain processes Cloud evaporation Observations of aerosol-cloud interactions In situ observations of cloud properties Remote sensing of cloud properties Challenges in observing aerosol-cloud interactions Determining causality Assessments of radiative forcing Approaches for quantifying radiative forcing Quantifying the anthropogenic aerosol perturbation Radiative forcing, DeltaFaci Adjustments and effective radiative forcing, DeltaFacieff Overall assessment Modeling Clouds Cloud fraction and condensation Bulk and spectral microphysical schemes Aerosol-cloud interactions Droplet activation Precipitation and evaporation processes Model evaluation Research directions References Atmospheric and oceanic dynamical responses to changes in aerosol Fundamental aspects of how aerosol affects climate dynamics Aerosol radiative forcing Interactions between different regions and timescales Responses of global mean temperature and precipitation Atmospheric responses on regional scales Tropics Global monsoon Asian monsoons Africa: Sahel drought and recovery Australia Tropical storms Mid-high latitudes Oceanic responses Atlantic: Atlantic multi-decadal variability and Atlantic meridional overturning circulation Pacific: Pacific decadal oscillation Tropical Pacific: El Niño Southern Oscillation Indian Ocean Modeling Knowledge gaps, future challenges, and research directions Acknowledgments References Aerosol interactions with deep convective clouds Fundamental aspects of deep convective clouds Deep convective cloud dynamics Convective environment, buoyancy, and vertical motions Entrainment and detrainment Pressure perturbation fields Deep convective cloud microphysics Warm-phase microphysics Mixed-phase and ice-phase microphysics Aerosol effects on deep convective clouds Effects on cloud microphysics Effects on cloud dynamics Effects on precipitation Effects on cloud macrophysical properties and radiation Aerosol effects on severe storms Effects on tropical cyclones and mid-latitude cyclones Effects on mesoscale convective systems (MCSs) Effects on hail and tornadoes Effects on lightning Effects of deep convective clouds on aerosol particles and precursor gases Vertical transport and scavenging Cloud processing and aerosol regeneration Modeling Modeling aerosol interactions with deep convection at cloud-resolving scales Features of models at cloud-resolving scales Bulk and bin microphysics schemes Significant findings Modeling aerosol interactions with deep convection using coarse model grids Features of coarse-resolution models Significant findings Knowledge gaps, future challenges, and research directions Knowledge gaps and challenges Research directions Acknowledgments References Ice-nucleating particles and their effects on clouds and radiation The role of heterogeneous ice formation in defining cloud microphysics and radiative properties Shallow mixed-phase clouds Convective clouds Upper tropospheric ice clouds that form in situ Role of ice-nucleating particles in cloud feedbacks and climate sensitivity Shallow mixed-phase cloud feedbacks Deep convection and anvil cirrus cloud feedbacks In situ cirrus cloud feedbacks Our physical understanding of heterogeneous ice nucleation The stochastic nature of nucleation Site-specific nucleation Active site requirements in the mixed-phase versus cirrus regimes The different types of ice-nucleating particles INP types important in mixed-phase clouds INP types important for in situ cirrus clouds Modeling Modeling ice-nucleating particles Heterogeneous nucleation in mixed-phase clouds Ice nucleation in cirrus Global model simulations of INP effects on mixed-phase clouds Global model simulations of INP effects on cirrus Cloud-resolving simulations of INP effects Knowledge gaps, future challenges, and research directions Acknowledgments References Aerosol processes in high-latitude environments and the effects on climate Climatic features of the high-latitude regions Physical characteristics of high-latitude environments Atmospheric features of high-latitude environments The mean general circulation The Arctic dome Clouds High-latitude aerosol sources and processes High-latitude aerosol emissions Arctic Antarctica Long-range transport of aerosol to high latitudes Arctic Antarctica Aerosol processes at high latitudes New particle formation, growth, and secondary aerosol components Chemical aging and cloud processing Aerosol deposition processes High-latitude aerosol properties and trends The availability of measurements to define aerosol properties Aerosol microphysical and chemical properties at the surface-Seasonal cycles Arctic Antarctic Vertical profile of aerosol properties Arctic Antarctica Decadal aerosol trends at high latitudes Arctic Antarctica Aerosol effects on the climate of polar and subpolar regions Light-absorbing particles on ice and snow Local atmospheric aerosol-radiation interactions Local aerosol-cloud interactions Modeling Remote aerosol effects Local aerosol emissions Long-distance transport of aerosol Local aerosol-radiation interactions Local aerosol-cloud interactions Knowledge gaps, future challenges, and research directions References Volcanic emissions, aerosol processes, and climatic effects Volcanic gas and particle emissions Passive volcanic emissions Eruptive volcanic emissions Volcanic effects on climate Volcanic aerosol processes, properties, and mechanisms Aerosol processes and distribution Aerosol optical depth Radiative effects and forcing Climatic response Forensic volcanology: Records of eruptions and their climatic effects Eruption chronologies: When, where, and how big Records of the climatic effects of volcanic eruptions Modeling Model simulations of volcanic effects on climate Model evaluation and confidence in estimated radiative forcings and climate responses Knowledge gaps, future challenges, and research directions References Climate engineering Background Stratospheric aerosol climate engineering Natural stratospheric aerosol processes Stratospheric aerosol radiative properties The mechanisms of stratospheric aerosol climate engineering Sources of evidence Analogs Field and laboratory experiments Effects of stratospheric aerosol climate engineering on climate Uncertainties and open research questions Marine cloud brightening Natural marine aerosol-cloud processes The mechanisms of marine cloud brightening Sources of evidence Analogs Field experiments Effects of marine cloud brightening on climate Uncertainties and open research questions Practical aspects of climate engineering Modeling Representing climate engineering in models Different ways models can be used References Aerosols in climate and air quality policy Introduction: Why we need to link climate and air quality policies Historical background Aerosol particles as pollutants Particulate matter (PM) air quality guidelines Effects on human health Effects on vegetation and crops: Acid deposition and eutrophication Measurements of PM Aerosol pollutants and climate change Comparing short-lived climate forcers (SLCFs) and CO2-Climate metrics Climate-air quality interaction Effects of policies related to air quality and climate Co-benefits and trade-offs Modeling Regional and global emission scenarios Integrated assessment models References Index A B C D E F G H I J K L M N O P Q R S T U V W