CockroachDB Community License
- 2 Aerosol
- 3 Related terms:
- 4 Vertical Profiling of Aerosol Optical Properties From LIDAR Remote Sensing, Surface Visibility, and Columnar Extinction Measurements
- 5 RADIATION TRANSFER IN THE ATMOSPHERE | Radiation, Solar
- 6 Radiometry in the Optical Domain
- 7 Atmospheric Aerosols and Their Role in Climate Change
- 8 Phase Separation
- 9 AEROSOLS | Aerosol–Cloud Interactions and Their Radiative Forcing
- 10 Climate–Chemistry Interaction
- 11 AEROSOLS | Climatology of Tropospheric Aerosols
- 12 AEROSOLS | Role in Climate Change
- 13 Remote Sensing of Aerosols From Space: Retrieval of Properties and Applications
Please read this CockroachDB Community License Agreement (the “Agreement”) carefully before using CockroachDB (as defined below), which is offered by Cockroach Labs, Inc. or its affiliated Legal Entities (“Cockroach Labs”).
By downloading CockroachDB or using it in any manner, You agree that You have read and agree to be bound by the terms of this Agreement. If You are accessing CockroachDB on behalf of a Legal Entity, You represent and warrant that You have the authority to agree to these terms on its behalf and the right to bind that Legal Entity to this Agreement. Use of CockroachDB is expressly conditioned upon Your assent to all the terms of this Agreement, to the exclusion of all other terms.
1. Definitions. In addition to other terms defined elsewhere in this Agreement, the terms below have the following meanings.
(a) “CockroachDB” shall mean the SQL database software provided by Cockroach Labs, including both CockroachDB Core and CockroachDB Enterprise editions, as defined below.
(b) “CockroachDB Core” shall mean the open source version of CockroachDB, available free of charge at https://github.com/cockroachdb/cockroach
(c) “Cockroach Enterprise Edition” shall mean the additional features made available by Cockroach Labs, the use of which is subject to additional terms set out below.
(d) “Contribution” shall mean any work of authorship, including the original version of the Work and any modifications or additions to that Work or Derivative Works thereof, that is intentionally submitted Cockroach Labs for inclusion in the Work by the copyright owner or by an individual or Legal Entity authorized to submit on behalf of the copyright owner.For the purposes of this definition, “submitted” means any form of electronic, verbal, or written communication sent to Cockroach Labs or its representatives, including but not limited to communication on electronic mailing lists, source code control systems, and issue tracking systems that are managed by, or on behalf of, Cockroach Labs for the purpose of discussing and improving the Work, but excluding communication that is conspicuously marked or otherwise designated in writing by the copyright owner as “Not a Contribution.”
(e) “Contributor” shall mean any copyright owner or individual or Legal Entity authorized by the copyright owner, other than Cockroach Labs, from whom Cockroach Labs receives a Contribution that Cockroach Labs subsequently incorporates within the Work.
(f) “Derivative Works” shall mean any work, whether in Source or Object form, that is based on (or derived from) the Work, such as a translation, abridgement, condensation, or any other recasting, transformation, or adaptation for which the editorial revisions, annotations, elaborations, or other modifications represent, as a whole, an original work of authorship. For the purposes of this License, Derivative Works shall not include works that remain separable from, or merely link (or bind by name) to the interfaces of, the Work and Derivative Works thereof.
(g) “Legal Entity” shall mean the union of the acting entity and all other entities that control, are controlled by, or are under common control with that entity.For the purposes of this definition, “control” means (i) the power, direct or indirect, to cause the direction or management of such entity, whether by contract or otherwise, or (ii) ownership of fifty percent (50%) or more of the outstanding shares, or (iii) beneficial ownership of such entity.
(h) “License” shall mean the terms and conditions for use, reproduction, and distribution of a Work as defined by this Agreement.
(i) “Licensor” shall mean Cockroach Labs or a Contributor, as applicable.
(j) “Object” form shall mean any form resulting from mechanical transformation or translation of a Source form, including but not limited to compiled object code, generated documentation, and conversions to other media types.
(k) “Source” form shall mean the preferred form for making modifications, including but not limited to software source code, documentation source, and configuration files.
(l) “Third Party Works” shall mean Works, including Contributions, and other technology owned by a person or Legal Entity other than Cockroach Labs, as indicated by a copyright notice that is included in or attached to such Works or technology.
(m) “Work” shall mean the work of authorship, whether in Source or Object form, made available under a License, as indicated by a copyright notice that is included in or attached to the work.
(n) “You” (or “Your”) shall mean an individual or Legal Entity exercising permissions granted by this License.
(a) License to CockroachDB Core.The License for CockroachDB Core is the Apache License, Version 2.0 (“Apache License”). The Apache License includes a grant of patent license, as well as redistribution rights that are contingent on several requirements. Please see http://www.apache.org/licenses/LICENSE-2.0 for full terms. CockroachDB Core is a no-cost, entry-level license and as such, contains the following disclaimers: NOTWITHSTANDING ANYTHING TO THE CONTRARY HEREIN, COCKROACHDB CORE IS PROVIDED “AS IS” AND “AS AVAILABLE”, AND ALL EXPRESS OR IMPLIED WARRANTIES ARE EXCLUDED AND DISCLAIMED, INCLUDING WITHOUT LIMITATION THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, NON-INFRINGEMENT, AND ANY WARRANTIES ARISING BY STATUTE OR OTHERWISE IN LAW OR FROM COURSE OF DEALING, COURSE OF PERFORMANCE, OR USE IN TRADE. For clarity, the terms of this Agreement, other than the relevant definitions in Section 1 and this Section 2(a) do not apply to CockroachDB Core.
(b) License to CockroachDB Enterprise Edition.
i Grant of Copyright License: Subject to the terms of this Agreement, Licensor hereby grants to You a worldwide, non-exclusive, non-transferable limited license to reproduce, prepare Enterprise Derivative Works (as defined below) of, publicly display, publicly perform, sublicense, and distribute CockroachDB Enterprise Edition for Your business purposes, for so long as You are not in violation of this Section 2(b) and are current on all payments required by Section 4 below.
ii Grant of Patent License: Subject to the terms of this Agreement, Licensor hereby grants to You a worldwide, non-exclusive, non-transferable limited patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer CockroachDB Enterprise Edition, where such license applies only to those patent claims licensable by Licensor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed.
iii License to Third Party Works: From time to time Cockroach Labs may use, or provide You access to, Third Party Works in connection CockroachDB Enterprise Edition. You acknowledge and agree that in addition to this Agreement, Your use of Third Party Works is subject to all other terms and conditions set forth in the License provided with or contained in such Third Party Works. Some Third Party Works may be licensed to You solely for use with CockroachDB Enterprise Edition under the terms of a third party License, or as otherwise notified by Cockroach Labs, and not under the terms of this Agreement. You agree that the owners and third party licensors of Third Party Works are intended third party beneficiaries to this Agreement.
3. Support. From time to time, in its sole discretion, Cockroach Labs may offer professional services or support for CockroachDB, which may now or in the future be subject to additional fees.
4. Fees for CockroachDB Enterprise Edition or CockroachDB Support.
(a) Fees. The License to CockroachDB Enterprise Edition is conditioned upon Your payment of the fees specified on /pricing/ which You agree to pay to Cockroach Labs in accordance with the payment terms set out on that page. Any professional services or support for CockroachDB may also be subject to Your payment of fees, which will be specified by Cockroach Labs when you sign up to receive such professional services or support. Cockroach Labs reserves the right to change the fees at any time with prior written notice; for recurring fees, any such adjustments will take effect as of the next pay period.
(b) Overdue Payments and Taxes. Overdue payments are subject to a service charge equal to the lesser of 1.5% per month or the maximum legal interest rate allowed by law, and You shall pay all Cockroach Labs’ reasonable costs of collection, including court costs and attorneys’ fees. Fees are stated and payable in U.S. dollars and are exclusive of all sales, use, value added and similar taxes, duties, withholdings and other governmental assessments (but excluding taxes based on Cockroach Labs’ income) that may be levied on the transactions contemplated by this Agreement in any jurisdiction, all of which are Your responsibility unless you have provided Cockroach Labs with a valid tax-exempt certificate.
(c) Record-keeping and Audit. If fees for CockroachDB Enterprise Edition are based on the number of cores or servers running on CockroachDB Enterprise Edition or another use-based unit of measurement, You must maintain complete and accurate records with respect Your use of CockroachDB Enterprise Edition and will provide such records to Cockroach Labs for inspection or audit upon Cockroach Labs’ reasonable request. If an inspection or audit uncovers additional usage by You for which fees are owed under this Agreement, then You shall pay for such additional usage at Cockroach Labs’ then-current rates.
5. Trial License. If You have signed up for a trial or evaluation of CockroachDB Enterprise Edition, Your License to CockroachDB Enterprise Edition is granted without charge for the trial or evaluation period specified when You signed up, or if no term was specified, for thirty (30) calendar days, provided that Your License is granted solely for purposes of Your internal evaluation of Cockroach Enterprise Edition during the trial or evaluation period (a “Trial License”). You may not use CockroachDB Enterprise Edition under a Trial License more than once in any twelve (12) month period. Cockroach Labs may revoke a Trial License at any time and for any reason. Sections 3, 4, 9 and 11 of this Agreement do not apply to Trial Licenses.
6. Redistribution. You may reproduce and distribute copies of the Work or Derivative Works thereof in any medium, with or without modifications, and in Source or Object form, provided that You meet the following conditions:
(a) You must give any other recipients of the Work or Derivative Works a copy of this License; and
(b) You must cause any modified files to carry prominent notices stating that You changed the files; and
(c) You must retain, in the Source form of any Derivative Works that You distribute, all copyright, patent, trademark, and attribution notices from the Source form of the Work, excluding those notices that do not pertain to any part of the Derivative Works; and
(d) If the Work includes a “NOTICE” text file as part of its distribution, then any Derivative Works that You distribute must include a readable copy of the attribution notices contained within such NOTICE file, excluding those notices that do not pertain to any part of the Derivative Works, in at least one of the following places: within a NOTICE text file distributed as part of the Derivative Works; within the Source form or documentation, if provided along with the Derivative Works; or, within a display generated by the Derivative Works, if and wherever such third-party notices normally appear. The contents of the NOTICE file are for informational purposes only and do not modify the License.You may add Your own attribution notices within Derivative Works that You distribute, alongside or as an addendum to the NOTICE text from the Work, provided that such additional attribution notices cannot be construed as modifying the License.
You may add Your own copyright statement to Your modifications and may provide additional or different license terms and conditions for use, reproduction, or distribution of Your modifications, or for any such Derivative Works as a whole, provided Your use, reproduction, and distribution of the Work otherwise complies with the conditions stated in this License.
(e) Enterprise Derivative Works: Derivative Works of CockroachDB Enterprise Edition (“Enterprise Derivative Works”) may be made, reproduced and distributed in any medium, with or without modifications, in Source or Object form, provided that each Enterprise Derivative Work will be considered to include a License to CockroachDB Enterprise Edition and thus will be subject to the payment of fees to Cockroach Labs by any user of the Enterprise Derivative Work.
7. Submission of Contributions. Unless You explicitly state otherwise, any Contribution intentionally submitted for inclusion in CockroachDB by You to Cockroach Labs shall be under the terms and conditions of https://cla-assistant.io/cockroachdb/cockroach (which is based off of the Apache License), without any additional terms or conditions, payments of royalties or otherwise to Your benefit. Notwithstanding the above, nothing herein shall supersede or modify the terms of any separate license agreement You may have executed with Cockroach Labs regarding such Contributions.
8. Trademarks. This License does not grant permission to use the trade names, trademarks, service marks, or product names of Licensor, except as required for reasonable and customary use in describing the origin of the Work and reproducing the content of the NOTICE file.
9. Limited Warranty.
(a) Warranties.Cockroach Labs warrants to You that: (i) CockroachDB Enterprise Edition will materially perform in accordance with the applicable documentation for ninety (90) days after initial delivery to You; and (ii) any professional services performed by Cockroach Labs under this Agreement will be performed in a workmanlike manner, in accordance with general industry standards.
(b) Exclusions. Cockroach Labs’ warranties in this Section 9 do not extend to problems that result from: (i) Your failure to implement updates issued by Cockroach Labs during the warranty period; (ii) any alterations or additions (including Enterprise Derivative Works and Contributions) to CockroachDB not performed by or at the direction of Cockroach Labs; (iii) failures that are not reproducible by Cockroach Labs; (iv) operation of CockroachDB Enterprise Edition in violation of this Agreement or not in accordance with its documentation; (v) failures caused by software, hardware or products not licensed or provided by Cockroach Labs hereunder; or (vi) Third Party Works.
(c) Remedies. In the event of a breach of a warranty under this Section 9, Cockroach Labs will, at its discretion and cost, either repair, replace or re-perform the applicable Works or services or refund a portion of fees previously paid to Cockroach Labs that are associated with the defective Works or services. This is Your exclusive remedy, and Cockroach Labs’ sole liability, arising in connection with the limited warranties herein.
10. Disclaimer of Warranty. Except as set out in Section 9, unless required by applicable law, Licensor provides the Work (and each Contributor provides its Contributions) on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied, arising out of course of dealing, course of performance, or usage in trade, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, CORRECTNESS, RELIABILITY, or FITNESS FOR A PARTICULAR PURPOSE, all of which are hereby disclaimed. You are solely responsible for determining the appropriateness of using or redistributing Works and assume any risks associated with Your exercise of permissions under the applicable License for such Works.
11. Limited Indemnity.
(a) Indemnity. Cockroach Labs will defend, indemnify and hold You harmless against any third party claims, liabilities or expenses incurred (including reasonable attorneys’ fees), as well as amounts finally awarded in a settlement or a non-appealable judgement by a court (“Losses”), to the extent arising from any claim or allegation by a third party that CockroachDB Enterprise Edition infringes or misappropriates a valid United States patent, copyright or trade secret right of a third party; provided that You give Cockroach Labs: (i) prompt written notice of any such claim or allegation; (ii) sole control of the defense and settlement thereof; and (iii) reasonable cooperation and assistance in such defense or settlement. If any Work within CockroachDB Enterprise Edition becomes or, in Cockroach Labs’ opinion, is likely to become, the subject of an injunction, Cockroach Labs may, at its option, (A) procure for You the right to continue using such Work, (B) replace or modify such Work so that it becomes non-infringing without substantially compromising its functionality, or, if (A) and (B) are not commercially practicable, then (C) terminate Your license to the allegedly infringing Work and refund to You a prorated portion of the prepaid and unearned fees for such infringing Work. The foregoing states the entire liability of Cockroach Labs with respect to infringement of patents, copyrights, trade secrets or other intellectual property rights.
(b) Exclusions. The foregoing obligations shall not apply to: (i) Works modified by any party other than Cockroach Labs (including Enterprise Derivative Works and Contributions), if the alleged infringement relates to such modification, (ii) Works combined or bundled with any products, processes or materials not provided by Cockroach Labs where the alleged infringement relates to such combination, (iii) use of a version of CockroachDB Enterprise Edition other than the version that was current at the time of such use, as long as a non-infringing version had been released, (iv) any Works created to Your specifications, (v) infringement or misappropriation of any proprietary right in which You have an interest, or (vi) Third Party Works. You will defend, indemnify and hold Cockroach Labs harmless against any Losses arising from any such claim or allegation, subject to conditions reciprocal to those in Section 11(a).
12. Limitation of Liability. In no event and under no legal or equitable theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts), and notwithstanding anything in this Agreement to the contrary, shall Licensor or any Contributor be liable to You for (i) any amounts in excess, in the aggregate, of the fees paid by You to Cockroach Labs under this Agreement in the twelve (12) months preceding the date the first cause of liability arose), or (ii) any indirect, special, incidental, punitive, exemplary, reliance, or consequential damages of any character arising as a result of this Agreement or out of the use or inability to use the Work (including but not limited to damages for loss of goodwill, profits, data or data use, work stoppage, computer failure or malfunction, cost of procurement of substitute goods, technology or services, or any and all other commercial damages or losses), even if such Licensor or Contributor has been advised of the possibility of such damages. THESE LIMITATIONS SHALL APPLY NOTWITHSTANDING THE FAILURE OF THE ESSENTIAL PURPOSE OF ANY LIMITED REMEDY.
13. Accepting Warranty or Additional Liability. While redistributing Works or Derivative Works thereof, and without limiting your obligations under Section 6, You may choose to offer, and charge a fee for, acceptance of support, warranty, indemnity, or other liability obligations and/or rights consistent with this License. However, in accepting such obligations, You may act only on Your own behalf and on Your sole responsibility, not on behalf of any other Contributor, and only if You agree to indemnify, defend, and hold Cockroach Labs and each other Contributor harmless for any liability incurred by, or claims asserted against, such Contributor by reason of your accepting any such warranty or additional liability.
(a) Relationship of Parties. You and Cockroach Labs are independent contractors, and nothing herein shall be deemed to constitute either party as the agent or representative of the other or both parties as joint venturers or partners for any purpose.
(b) Export Control. You shall comply with the U.S. Foreign Corrupt Practices Act and all applicable export laws, restrictions and regulations of the U.S. Department of Commerce, and any other applicable U.S. and foreign authority.
(c) Assignment. This Agreement and the rights and obligations herein may not be assigned or transferred, in whole or in part, by You without the prior written consent of Cockroach Labs. Any assignment in violation of this provision is void.This Agreement shall be binding upon, and inure to the benefit of, the successors and permitted assigns of the parties.
(d) Governing Law. This Agreement shall be governed by and construed under the laws of the State of New York and the United States without regard to conflicts of laws provisions thereof, and without regard to the Uniform Computer Information Transactions Act.
(e) Attorneys’ Fees. In any action or proceeding to enforce rights under this Agreement, the prevailing party shall be entitled to recover its costs, expenses and attorneys’ fees.
(f) Severability. If any provision of this Agreement is held to be invalid, illegal or unenforceable in any respect, that provision shall be limited or eliminated to the minimum extent necessary so that this Agreement otherwise remains in full force and effect and enforceable.
(g) Entire Agreement; Waivers; Modification. This Agreement constitutes the entire agreement between the parties relating to the subject matter hereof and supersedes all proposals, understandings, or discussions, whether written or oral, relating to the subject matter of this Agreement and all past dealing or industry custom. The failure of either party to enforce its rights under this Agreement at any time for any period shall not be construed as a waiver of such rights. No changes, modifications or waivers to this Agreement will be effective unless in writing and signed by both parties.
An aerosol is a suspension of liquid or solid particles in a gas, with particle diameters in the range of 10−9 to 10−4 m.
Download as PDF
About this page
Vertical Profiling of Aerosol Optical Properties From LIDAR Remote Sensing, Surface Visibility, and Columnar Extinction Measurements
Atmospheric aerosols are generating from the Earth’s surface except from aviation emissions or meteorite debris. The height of aloft aerosol layers is a critical determinant of global aerosol transport and dispersion. Despite its importance in geo-locational characteristics of aerosols, aerosols vertical information is typically unknown. Aerosol vertical profile is an important parameter for understanding the radiative effects of aerosols and for generating more accurate aerosol models. With the development and improvement of the remote sensing techniques, the integrated dataset from both active and passive remote sensing techniques have been provided a comprehensive observation of aerosols and radiation which are urgently required for air quality and climatic study. Ground-based sensors or satellite observations are well-developed and used for measuring aerosol vertical profiles. In this chapter, measurement techniques for the aerosol vertical profiles is explained and discussed, which is estimated using integrated data from ground-based measurement, satellite observation, radiative transfer model (RTM) calculation.
RADIATION TRANSFER IN THE ATMOSPHERE | Radiation, Solar
Effects of Aerosols on Solar Radiation
Aerosols are suspensions of liquid and solid particles in the atmosphere, excluding clouds and precipitation. The aerosol particle sizes range from 10 −4 to 10 μm, falling under the following broad categories: sulfates, black carbon, organic carbon, dust, and sea salt. Aerosol concentrations and compositions vary significantly with time and location. Visibility measurements reflect the aerosol concentration at ground level. The visual range can vary from a few meters to 200 km, depending on the proximity to sources, the strength of the sources, and atmospheric conditions.
Aerosols scatter and absorb solar radiation. Sulfate aerosols scatter primarily solar radiation and cause cooling of the Earth–atmosphere system. The increase in the reflected solar radiation at the top of the atmosphere due to such nonabsorbing aerosols is nearly identical to the reduction in the solar radiation at the surface. Carbonaceous aerosols (black carbon and organics) absorb and scatter solar radiation. The presence of black carbon aerosols results in the absorption of solar radiation, which reduces the solar radiation reaching the surface. At the same time, these aerosols absorb the upward solar radiation reflected from below and reduce the solar radiation reflected to space. Therefore, the effect of black carbon aerosols opposes the cooling effect of other aerosols at the top of the atmosphere, whereas at the surface all aerosols reduce the solar radiation. The changes arising from the aerosol scattering and absorption of solar radiation are referred to as their direct radiative forcing. Aerosols can also modify the solar radiation through their role in cloud condensation and as ice nuclei, an effect known as aerosol indirect radiative forcing.
Aerosol particles in the atmosphere are produced both in nature and by people. A global aerosol optical depth of about 0.12 is suggested. These aerosols increase the reflected solar radiation at the top of the atmosphere by about 3 W m −2 globally. Anthropogenic sources contribute significantly to the global aerosol optical depth. Global anthropogenic emissions of sulfates, organics, and black carbon even exceed natural sources. Such a large perturbation of the global aerosol loading due to human activities may significantly modify regional and global climates.
Radiometry in the Optical Domain
Aerosols are defined as a combination of liquid or solid particles suspended in a gaseous or liquid environment. In the atmosphere, these particles are mainly situated in the low layers of the atmosphere ( 1.5 km) since aerosol sources are located on the terrestrial surface. However, certain aerosols can still be found in the stratosphere, especially volcanic aerosols ejected into the high altitude layers.
The origin of atmospheric aerosols is either natural or the result of anthropogenic activities. They are usually classified as a function of their composition and origin:
terrigenous aerosols or dust: these aerosols come from continental surfaces such as deserts or bare soil. They are mainly composed of clay, quartz, feldspar and calcite. They are injected into the atmosphere by the uplifting of particles on the ground due to wind. The smallest particles can travel distances higher than a thousand kilometers. These aerosols are found in the highest quantity in the atmosphere;
oceanic aerosols and sea spray: as their name indicates, these come from maritime regions. They are formed by waves (sea spray) and by the evaporation of water on the ocean surface;
soluble aerosols: this term designates a large number of aerosols, especially sulfates, which are very present in urban environments. Soluble aerosols also include nitrates. They mainly come from cities, industrial sites and vegetation;
combustion aerosols: these aerosols are a result of biomass and domestic fires, industrial emissions and traffic;
volcanic aerosols: these aerosols are mainly composed of sulfur dioxide emitted by volcanic eruptions and thrown into the stratosphere. As a result of their injection into this part of the atmosphere, they can progressively spread throughout the entire globe.
Atmospheric Aerosols and Their Role in Climate Change
Atmospheric aerosols consist of solid/aqueous particles suspended in the atmosphere and are typically of sizes in the range 0.001 μm–10 μm. Aerosols are generated from a wide range of natural and anthropogenic sources. Natural aerosols include sulphate aerosols that are formed from emissions of sulphur dioxide from volcanic eruptions or from dimethyl sulphide emissions from phytoplankton in the ocean, sea salt particles emitted at the ocean surface, or mineral dust aerosol that is emitted by the effects of wind erosion on arid land. Anthropogenic aerosols, i.e. those that are generated from human activities, include sulphate, nitrate, black carbon and organic carbon aerosols from fossil fuel burning, deforestation fires and burning of agricultural waste.
Aerosols scatter and absorb sunlight and terrestrial radiation and therefore increased concentrations of atmospheric aerosols from anthropogenic activities such as fossil fuel burning and biomass burning lead to modifications of Earth’s energy balance and hence modulate climate. Atmospheric aerosols can also act as cloud condensation nuclei and can change the microphysical and radiative properties and hence the lifetime of clouds and further modulate climate. Furthermore, emissions of natural aerosols may be enhanced or reduced in response to changes in climate. For example, should future climate lead to a reduction in soil moisture in a particular area and consequently increase the spatial extent of arid areas, then mineral dust emissions may increase and dust particles will interact with sunlight and terrestrial radiation, further affecting climate. These responses to climate change are known as climate feedback mechanisms, and aerosols are explicitly coupled to the climate system through them.
Here we will describe the life cycle of aerosols in the lowest layer of the atmosphere known as the troposphere and present estimates of their current global distribution (stratospheric aerosols are presented in detail in Chapter 26 ). We will then use simple approximations to gain a physical understanding of the important parameters associated with atmospheric aerosols in quantifying aerosol-radiation interactions and aerosol-cloud interactions. The role of aerosols in climate feedback mechanisms will be discussed, and recent work on the potential role of aerosols in geoengineering schemes that aim to counterbalance the impacts of global warming will be presented.
Aerosols are formed by three mechanisms: condensation, atomization, and entrainment. The relative sizes produced by these formation mechanisms are given in Fig. 5.7 .
Figure 5.7 . Aerosol types ( Brown et al., 1994 ).
Aerosols formed by condensation of a vapor into a liquid are the smallest and most difficult to remove contaminants having a size distribution in the range of 0.2–5 microns. Atomization creates aerosol drops by breaking up larger liquid drops through mechanical shear such as passing through a constriction in a valve under a high velocity. Atomization forms aerosols in the size range of 10–200 microns. Entrainment involves the movement of liquid slugs along pipelines, and here the liquid drop sizes are very large from 500 to 5000 microns. All three types of aerosol liquids are commonly found in gas systems. High-efficiency liquid–gas coalescers can effectively remove the fine aerosols created by the condensation mechanism.
AEROSOLS | Aerosol–Cloud Interactions and Their Radiative Forcing
Aerosols are essential for cloud formation. Every cloud droplet needs an aerosol particle, called cloud condensation nucleus (CCN), for activation. Likewise ice crystals either form on a subset of aerosol particles that act as ice nuclei (IN) or form by homogeneous freezing of supercooled solution drops (liquid aerosols that took up water). In the absence of aerosols, several 100% relative humidity (RH) would be necessary for cloud droplets to form by homogeneous nucleation from supersaturated water vapor. Due to the ubiquitous presence of CCN, the RH in water clouds hardly exceeds 101%. The situation is different for ice clouds because IN are sparse, and formation of cirrus clouds is dominated by homogeneous freezing of solution droplets. This takes place at relative humidities below 100% with respect to water but well above 100% with respect to ice (at −60 °C the RH for homogeneous freezing is 150%). At the same time, removal of aerosols by clouds and precipitation is the largest sinks for aerosols with diameters
13.4.1 The Role of Sulfate Aerosols as a Climatically-Active Compound
Sulfate aerosols , either naturally produced or anthropogenerated, have been studied extensively. The sulfur cycle involving production, chemical conversion, transport, and removal of sulfate aerosol exemplifies a typical lifecycle of trace chemicals in the atmosphere. Other types of aerosols may also experience a similar lifecycle, although without strong chemical conversions (such as mineral dust and BC), while other chemical conversions are too complicated and not fully understood (such as OAs). We use sulfate as an example to demonstrate aerosol climate–chemistry interactions, with an added note that, unlike mineral dust and BC aerosols, which have strong absorption of solar radiation, sulfate aerosols mainly reflect solar radiation.
AEROSOLS | Climatology of Tropospheric Aerosols
Atmospheric aerosols are solid and liquid particles in suspension in the air, ranging in size from a few nanometers to tens of microns (10 −9 –10 −5 m), with the exception of cloud droplets and ice crystals. Natural sources of aerosols include sea salt generated from breaking waves, mineral dust blown from the surface by wind, and organic aerosols from biogenic emissions. Artificial, also called anthropogenic, aerosols include sulfate, nitrate, and carbonaceous aerosols, and are mainly from fossil fuel combustion sources. The first aerosol studies were motivated by visibility, and in 1880 the British scientist John Aitken correctly postulated that aerosol particles act as nuclei for the condensation of water vapor to form fog and clouds. In the second part of the twentieth century, aerosol particles were linked to an increase in human respiratory diseases and acid rain, prompting the need to improve air quality by reducing emissions of aerosols and their precursors. At the same time, scientists started quantifying the impact of aerosols on the Earth’s energy budget and simple aerosol representations were introduced in weather forecast and climate models. Climatologies of aerosols in the troposphere have been developed over time, tailored to the diverse interests in aerosol properties. Climatologies of aerosol surface concentrations and chemical composition originate from air quality monitoring networks such as the European Monitoring and Evaluation Programme and the Clean Air Status and Trends Network of the United States Environmental Protection Agency. Dedicated instrumented aircraft campaigns provide regional snapshots of aerosol composition and size across the lower atmosphere, including information on aerosol microphysical properties and vertical profiles. Networks of remote sensing instruments have been deployed at selected sites worldwide, forming for example the Aerosol Robotic Network (AERONET). AERONET sun photometers provide measurements of the column-integrated extinction of visible or near-infrared radiation by aerosols, called optical depth, and these measurements can be inverted to provide an estimate of aerosol size. The launch of dedicated satellite instruments beginning in the late 1990s provides a global view of aerosol distributions of optical depth. More recently, vertical aerosol distribution has been routinely observed by lidars, located on the ground, aboard aircrafts, or on satellite platforms. In parallel to improved observational capabilities, numerical models have developed and provide daily aerosol forecasts, increasingly often initialized from assimilation of satellite observations, as well as centennial simulations for climate projections. Numerical models vary in the number of aerosol species they include and in the number of aerosol characteristics they are able to represent depending on the need for computational speed.
In spite of those diverse sources of data, there are a number of difficulties associated with obtaining the aerosol climatology that fits a given application. By definition, aerosols encompass a large range of particle sizes and chemical compositions. Their sources are very diverse and unevenly distributed across the globe. Aerosols are removed from the atmosphere primarily by spatially inhomogeneous precipitation processes and, to a smaller extent, turbulence. Thus, aerosols have a relatively short residence time in the troposphere of typically up to 1 or 2 weeks. Consequently, aerosol concentrations vary greatly in time and space, both horizontally and vertically, in contrast to well-mixed greenhouse gases like carbon dioxide. Well-defined aerosol plumes can often be identified in observations, with aerosol number and mass varying by orders of magnitudes within a few kilometers in the horizontal and a few hundred or even a few tens of meters in the vertical across the plume. Measurements at the surface may therefore not be indicative of aerosol concentrations and properties higher up in the atmosphere. There are also several ways to characterize aerosols. Since aerosols are typically present in large numbers in the atmosphere, their population is described by its size distribution, which gives the number, surface area, or volume of the particles as a function of their radii. As depicted in Figure 1 , a typical tropospheric aerosol size distribution exhibits several maxima, called modes. The smaller particles, with radii smaller than 50 nm, belong to the nucleation and Aitken modes and provide most of the total aerosol number. The accumulation mode covers particles with radii up to 0.5 μm, which dominate the aerosol surface area. Both Aitken and accumulation modes are often called fine modes to contrast with the coarse mode, which comprises particles larger than 0.5 μm and makes up the bulk of aerosol volume. Minima in the size distribution arise from coagulation processes, where smaller particles of favorable sizes aggregate into larger particles. Air quality networks routinely report aerosol concentrations for particles with aerodynamic diameters smaller than 2.5 and 10 μm, labeled Particulate Matter (PM) 2.5 and PM10, respectively. Air quality regulations impose thresholds on both the annual average and daily average of PM concentrations in many countries. In Europe, daily average PM10 concentrations should not exceed 50 μg m −3 for more than 35 days per year. In newly industrialized countries, where air quality regulation is weaker, PM10 concentrations routinely exceed 100 μg m −3 on an annual average.
Figure 1 . Distribution of the volume of aerosol particles as a function of their radii, as sampled by the Facility for Airborne Atmospheric Measurements aircraft (black lines) and inverted from ground-based sun-photometer measurements of the Aerosol Robotic Network (gray lines). Panels gather measurements of generic aerosol types at different locations: (a) Industrial aerosol, (b) Mineral dust aerosol, (c) Biomass-burning aerosol, and (d) Marine aerosol.
Osborne, S.R., Haywood, J.M., 2005. Aircraft observations of the microphysical and optical properties of major aerosol species. Atmospheric Research 73, 173–201. © Crown.
Aerosols are also characterized by their production processes and chemical composition. Primary aerosols are emitted into the atmosphere directly as particles. They include the carbonaceous by-products of incomplete combustion processes and wind-blown mineral dust aerosols. In contrast, secondary aerosols originate from gas-to-particle conversions. Gaseous precursors, such as sulfur dioxide and ammonia, are oxidized in the dry atmosphere or in clouds and become soluble in water. Eventually, a large fraction of the emitted precursor enters the aerosol phase, dissolved in a droplet. As such, water represents a sizable fraction of the total aerosol mass. Gas-to-particle conversion processes also mean that aerosols are part of the chemistry of the atmosphere and indirectly affect the concentrations of gaseous species such as ozone and methane. Aerosol populations are typically of diverse chemical composition and their mixing state can be both internal, where the mixed composition lies within the same particle, and external, where each particle has a chemically distinct composition. Particle size can be a simplified marker of the production process. Fine-mode aerosols often originate from gas-to-particle conversion or combustion processes. Coarse-mode particles typically originate from mechanical processes such as wind friction. The shape of the particles also depends on the production process: aerosol solutions are spherical droplets. Combustion aerosols, grains of mineral dust, and pollens have more complex, irregular shapes.
Aerosols can finally be characterized by their natural or anthropogenic origin. This distinction is difficult to obtain from observations alone, but is important for climate studies. Aerosols emitted into the atmosphere by human activities since the start of the industrial revolution have scattered and absorbed additional solar and thermal radiation. They also have modified cloud droplet sizes and number, again affecting solar radiation, albeit indirectly. In effect, anthropogenic aerosols have changed the radiative balance of the Earth in a process called radiative forcing. Although uncertain, this forcing is estimated to be negative, and the climate system responds by cooling. Estimates for the year 2000 suggest that aerosol forcing compensates two-thirds of the positive forcing by long-lived greenhouse gases. Local climate changes driven by anthropogenic emissions can also affect emissions of natural aerosols, desertification being a typical example. In that case, the anthropogenic or natural classification of the aerosol is not obvious.
AEROSOLS | Role in Climate Change
Aerosols , the liquid and solid particles in suspension in the atmosphere, matter to the scientific study of climate change for three reasons. First, they are optically active species, interacting with solar and terrestrial radiation directly by scattering and absorption, and indirectly by modifying the microphysical properties of clouds and the radiative properties of surfaces covered by snow and ice. Perturbations to atmospheric distributions of aerosols therefore translate into perturbations of the Earth’s radiative budget, which can enhance or counteract the radiative perturbations exerted by changes in the concentrations of long-lived greenhouse gases such as carbon dioxide and methane.
Second, human activities have profoundly perturbed aerosol distributions. Since the start of the Industrial Revolution in the eighteenth century, road transport, aviation, maritime shipping, industries, power plants, domestic cooking stoves, and forest-clearing fires have all emitted aerosols and their gaseous precursors, increasing the amount of particles in the atmosphere and modifying their chemical composition. Figure 1 (a) shows a time series of globally averaged emissions of the main anthropogenic aerosol and precursor species since the year 1850. According to those estimates, anthropogenic emissions of sulfur dioxide, the gaseous precursor to sulfate aerosols, have risen from a global total of 2 Tg for the year 1850 to more than 120 Tg per year at the end of the twentieth century. Over the same period, primary emissions of carbonaceous aerosols from fossil fuel combustion, and emissions of ammonia, the precursor of nitrate aerosols, increased by a factor 3. Increases in emissions increase aerosol mass over the source region and transport pathways, as illustrated by Figure 1 (b), which shows changes in surface concentrations of sulfate aerosols over the industrial period. Increases do not cover the whole globe because strong sinks, dominated by washout by precipitation, prevent aerosols from accumulating in the atmosphere. The very heterogeneous distribution of aerosol concentrations and compositions in the atmosphere complicates the study of their climatic role compared to that of well-mixed and long-lived greenhouse gases such as carbon dioxide.
Figure 1 . (a) Left panel: Time series of global, annual anthropogenic emissions of sulfur dioxide, ammonia, and primary carbonaceous aerosols over the period 1850–2000 according to the CMIP5 data set. (b) Right panel: Modeled changes in column-integrated concentrations of sulfate aerosols, in mg[S] m −2 , due to changes in anthropogenic emissions of sulfur dioxide over the period 1850–2000.
The third and last reason why aerosols play an important role in climate change is the dependence of their sources and sinks on the state of the climate. As climate responds to an initial radiative perturbation, the distributions of natural and anthropogenic aerosols and their gaseous precursors change, giving rise to radiative feedbacks that either oppose or reinforce the initial radiative perturbation. The Introduction section of this article introduces the three important concepts of radiative forcing (RF), fast adjustments, and climate response, which are relevant to the multiple roles of aerosols in climate change. Section Instantaneous and Effective RF, and Climate Response then reviews the mechanisms through which aerosols perturb the Earth’s RF, while Section Mechanisms of Aerosol RF discusses how aerosols are in turn influenced by climate change. Finally, the proposed use of aerosols as tools for climate mitigation is discussed in Section Climate Response and Aerosol Feedbacks .
Remote Sensing of Aerosols From Space: Retrieval of Properties and Applications
Atmospheric aerosols are multicomponent mixtures typically composed of liquid and/or solid particles suspended in the atmosphere. Aerosols originate from numerous sources, having successively evolved through various microphysical processes before being removed either by wet or dry depositions. The implications of these airborne particulates on the regional and global climate are many but most notably through regulating the atmospheric heat budget either by absorbing/scattering insolation or by modifying cloud microphysical properties. Global distributions of aerosols are typically regional; thereby, they pose a strong regional signature that induces additional uncertainties in estimating aerosols, induced climate forcing. Satellite remote sensing of aerosols has extensive applications in identifying aerosol columnar properties, especially in terms of optical depth, composition, morphology, and vertical distribution. This ultimately provides evidence in establishing the source-transport-receptor relations of aerosols over a synoptic scale. Further, satellite data of atmospheric compositions are often used for identifying pollutant emissions, transboundary movement, forecasting air quality, and, more recently, in associating air quality with human health. The principles of remote sensing of aerosols are quite different from that of trace gases as the extinction of light by aerosols is a function of wavelength. With the gradual advancement of sensing technologies, monitoring of atmospheric aerosols has become more precise. Therefore, it has become more widely applied in various academic disciplines, studies, policies, and decision-making processes. This article emphasizes the state of the art in the field of satellite remote sensing, specifically in terms of polar-orbiting satellites for tropospheric aerosols including both active- and passive-based observations; associated complexities and uncertainties; brief descriptions of data products; and the subsequent applications in climate science.