Aerosol medication

Putaud, J. P. et al. A European aerosol phenomenology-3: Physical and chemical characteristics of particulate matter from 60 rural, urban, and kerbside sites across Europe. Atmospheric Environment 44, 1308-1320 (2010).

Aerosols in pharmacy

Liao, H. & Seinfeld, J. H. Global impacts of gas-phase chemistry-aerosol interactions on direct radiative forcing by anthropogenic aerosols and ozone. Journal of Geophysical Research-Atmospheres 110, D18208 (2005).

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Primary aerosols consist of both inorganic and organic components. Inorganic primary aerosols are relatively large (often larger than 1 μm) and originate from sea spray, mineral dust, and volcanoes. These coarse aerosols have short atmospheric lifetimes, typically only a few days. Combustion processes, biomass burning, and plant/microbial materials are sources of carbonaceous aerosols, including both organic carbon (OC) and solid black carbon (BC). BC is the main anthropogenic light-absorbing constituent present in aerosols. Its main sources are the combustion of fossil fuels (such as gasoline, oil, and coal), wood, and other biomass. Primary BC and OC containing aerosols are generally smaller than 1 µm.

Aerosol vape

Hansen, J. et al. Radiative forcing and climate response. Journal of Geophysical Research-Atmospheres 102, 6831-6864 (1997).

Koch, D. & Del Genio, A. D. Black carbon semi-direct effects on cloud cover: review and synthesis. Atmospheric Chemistry and Physics 10, 7685-7696 (2010).

Types of aerosols

IPCC. The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change Cambridge, UK: Cambridge University Press, 2007

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Myhre, G. Consistency between satellite-derived and modeled estimates of the direct aerosol effect. Science 325, 187-190 (2009).

Knutti, R. & Hegerl, G. C. The equilibrium sensitivity of the Earth's temperature to radiation changes. Nature Geoscience 1, 735-743 (2008).

Schulz, M. et al. Radiative forcing by aerosols as derived from the AeroCom present-day and pre-industrial simulations. Atmospheric Chemistry and Physics 6, 5225-5246 (2006).

Figure 1: Sources and appearance of atmospheric aerosols.Top: local and large scale air pollution. Sources include (bottom, counterclockwise) volcanic eruptions (producing volcanic ash and sulphate), sea spray (sea salt and sulphate aerosols), desert storms (mineral dust), savannah biomass burning (BC and OC), coal power plants (fossil fuel BC and OC, sulphate, nitrate), ships (BC, OC, sulphates, nitrate), cooking* (domestic BC and OC), road transport (sulphate, BC, VOCs yielding OC). Center: Electron microscope images of (A) sulphates, (B) soot, (C) fly ash, a product of coal combustion (Posfai et al., 1999).© 2013 Nature Education Images courtesy of Eyjafjallajökull eruption: courtesy of Árni Friðriksson, Wikimedia commons; Sea spray: NASA/JPL; Desert storm: Wikimedia commons; Savannah biomass burning: Wikimedia Commons ; Coal power plants: Wikimedia Commons; Ship in a Norwegian fjord: Stefan Großmann, Wikimedia commons; Cooking: Fullerton et al.2009; Truck: U. S. EPA, Wikimedia commons. All rights reserved.

Aerosol Spray

Pósfai, M. et al. Soot and sulfate aerosol particles in the remote marine troposphere. Journal of Geophysical Research-Atmospheres 104, 21685-21693 (1999).

Graber, E. R. & Rudich, Y. Atmospheric HULIS: How humic-like are they? A comprehensive and critical review. Atmospheric Chemistry and Physics 6, 729-753 (2006).

Boucher, O. & Haywood, J. On summing the components of radiative forcing of climate change. Climate Dynamics 18, 297-302 (2001).

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Ramanathan, V. et al. Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze. Journal of Geophysical Research-Atmospheres 106, 28371-28398 (2001).

Secondary aerosol particles are produced in the atmosphere from precursor gases by condensation of vapours on pre-existing particles or by nucleation of new particles. A considerable fraction of the mass of secondary aerosols is formed through cloud processing (Ervens et al. 2011). Secondary aerosols are small; they range in size from a few nanometres up to 1 µm and have lifetimes of days to weeks. Secondary aerosols consist of mixtures of compounds; the main components are sulphate, nitrate, and OC. The main precursor gases are emitted from fossil fuel combustion, but fires and biogenic emissions of volatile organic compounds (VOCs) are also important. Occasionally volcanic eruptions result in huge amounts of primary and secondary aerosols both at the ground and in the stratosphere (Boulon et al. 2011). The size and chemical composition of the particles evolve with time through coagulation, condensation, and chemical reactions. Particles may grow by uptake of water, a process that depends on chemical composition, particle size, and ambient relative humidity. The different particles have varying impacts in the atmosphere depending on composition, and the numerous sources and large range in size distributions further complicate a quantification of their effects. Both particle growth and the mixing of different particle types influence the climate effect of aerosols.

Boulon, J. et al. Observations of nucleation of new particles in a volcanic plume. Proceedings of the National Academy of Sciences (USA) 108, 12223-12226 (2011).

Remer, L. A. et al. Global aerosol climatology from the MODIS satellite sensors. Journal of Geophysical Research-Atmospheres 113, D14s07 (2008).

Kaufman, Y. J. & Chou, M. D. Model simulations of the competing climatic effects of SO2 and CO2. Journal of Climate 6, 1241-1252 (1993).

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Figure 4: Aerosol functions.(a) Probability density functions of aerosol effects (Isaksen et al. (2009), with small updates of cloud albedo and lifetime effects). The total aerosol radiative forcing (red and blue curves), with and without clouds are estimated by combining the individual effects in a Monte Carlo calculation (Boucher & Haywood 2001). Vertical lines show 90% confidence intervals. (b) Climate sensitivity for a doubling of CO2 as a function of the total aerosol RF. Radiative imbalances of 0.85 (solid line, Hansen et al. 2005), 0.7 and 1.0 Wm-2 (grey band) and 0.0 (radiative equilibrium, dashed line) are shown. Industrial era temperature change is taken as 0.8 Kelvin (K), and RF of non-aerosol components +2.9 Wm-2.© 2013 Nature Education All rights reserved.

Stevens, B. & Feingold, G. Untangling aerosol effects on clouds and precipitation in a buffered system. Nature 461, 607-613 (2009).

Figure 3: The direct aerosol effect and the cloud albedo effect.(a) The direct aerosol effect for low and high surface albedo, for scattering and absorbing aerosols. A dark surface (low albedo) will already absorb a large portion of the solar radiation, and absorbing aerosols will thus have a small effect. Scattering aerosols will instead amplify the total reflectance of solar radiation, since the solar radiation would otherwise be absorbed at the surface. Over a bright surface (high albedo) scattering aerosols have a reduced effect. Absorbing aerosols may, however, substantially reduce the outgoing radiation and thus have a warming effect. (b) The cloud albedo effect (first indirect aerosol effect), cloud lifetime effect (second indirect aerosol effect), and semi-direct effect.© 2013 Nature Education All rights reserved.

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Kanakidou, M. et al. Organic aerosol and global climate modelling: A review. Atmospheric Chemistry and Physics 5, 1053-1123 (2005).

Lohmann, U. & Feichter, J. Impact of sulfate aerosols on albedo and lifetime of clouds: A sensitivity study with the ECHAM4 GCM. Journal of Geophysical Research-Atmospheres 102, 13685-13700 (1997).

Charlson, R. J. et al. Perturbation of the Northern-Hemisphere radiative balance by backscattering from anthropogenic sulfate aerosols. Tellus Series a-Dynamic Meteorology and Oceanography 43, 152-163 (1991).

If we assume a total aerosol RF and a current energy imbalance, we can compute the resulting climate sensitivity using Equation 1 (Figure 4b). This can then be compared with the PDFs for the current aerosol RF to get an indication of the range in climate sensitivities allowed by the present knowledge (red and blue lines in figure 4b). A similar figure has previously been presented in Andreae et al. (2005). The allowed climate sensitivity ranges from about 2 to 8 Kelvin (K) for a doubling of CO2 using the known industrial age warming of around 0.8 K, the present best knowledge of RF from non-aerosol components, the 90% confidence interval of the total aerosol RF for the most certain effects, and radiative imbalance.

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Holben, B. N. et al. AERONET - A federated instrument network and data archive for aerosol characterization. Remote Sensing of Environment 66, 1-16 (1998).

Koch, D. et al. Distinguishing Aerosol Impacts on Climate over the Past Century. Journal of Climate 22, 2659-2677 (2009).

What Is aerosol in Chemistry

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Haywood, J. M. & Shine, K. P. The effect of anthropogenic sulfate and soot aerosol on the clear-sky planetary radiation budget. Geophysical Research Letters 22, 603-606 (1995).

Menon, S. et al. GCM Simulations of the aerosol indirect effect: Sensitivity to cloud parameterization and aerosol burden. Journal of the Atmospheric Sciences 59, 692-713 (2002).

Isaksen, I. S. A. et al. Atmospheric composition change: Climate-chemistry interactions. Atmospheric Environment 43, 5138-5192 (2009).

All atmospheric aerosols scatter incoming solar radiation, and a few aerosol types can also absorb solar radiation. BC is the most important of the latter, but mineral dust and some OC components are also sunlight absorbers. Aerosols that mainly scatter solar radiation have a cooling effect, by enhancing the total reflected solar radiation from the Earth. Strongly absorbing aerosols have a warming effect. In the atmosphere, there is a mixture of scattering and absorbing aerosols, and their net effect on Earth's energy budget is dependent on surface and cloud characteristics. Scattering aerosols above a dark surface and absorbing aerosols above a bright surface are most efficient (see Figure 3a). Scattering (absorbing) aerosol above a bright (dark) surface are less efficient because the solar radiation is reflected (absorbed) anyway. Absorbing aerosols are particularly efficient when positioned above clouds, which are a main contributor to the total reflection of solar radiation back to space.

Atmospheric aerosols are suspensions of liquid, solid, or mixed particles with highly variable chemical composition and size distribution (Putaud et al. 2010). Their variability is due to the numerous sources and varying formation mechanisms (Figure 1). Aerosol particles are either emitted directly to the atmosphere (primary aerosols) or produced in the atmosphere from precursor gases (secondary aerosols).

Storelvmo, T. et al. Global modeling of mixed-phase clouds: The albedo and lifetime effects of aerosols. Journal of Geophysical Research-Atmospheres 116, D05207 (2011).

Ervens, B. et al. Secondary organic aerosol formation in cloud droplets and aqueous particles (aqSOA): a review of laboratory, field and model studies. Atmospheric Chemistry and Physics 11, 11069-11102 (2011).

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Lohmann, U. & Hoose, C. Sensitivity studies of different aerosol indirect effects in mixed-phase clouds. Atmospheric Chemistry and Physics 9, 8917-8934 (2009).

Jacobson, M. Z. Global direct radiative forcing due to multicomponent anthropogenic and natural aerosols. Journal of Geophysical Research-Atmospheres 106, 1551-1568 (2001).

Zhang, Q. et al. Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-influenced Northern Hemisphere midlatitudes. Geophysical Research Letters 34, L13801 (2007).

Aerosols are vital for cloud formation because a subset of them may serve as cloud condensation nuclei (CCN) and ice nuclei (IN). An increased amount of aerosols may increase the CCN number concentration and lead to more, but smaller, cloud droplets for fixed liquid water content. This increases the albedo of the cloud, resulting in enhanced reflection and a cooling effect, termed the cloud albedo effect (Twomey 1977; Figure 3b). Smaller drops require longer growth times to reach sizes at which they easily fall as precipitation. This effect, called the cloud lifetime effect, may enhance the cloud cover (see illustration in Figure 3b) and thus impose an additional cooling effect (Albrecht 1989). However, the life cycles of clouds are controlled by an intimate interplay between meteorology and aerosol-and-cloud microphysics, including complex feedback processes, and it has proven difficult to identify the traditional lifetime effect put forth by Albrecht (1989) in observational data sets. Absorbing aerosols also have the potential to modify clouds properties, without directly acting as CCN and IN, by: (1) heating the air surrounding them while reducing the amount of solar radiation reaching the ground, which stabilizes the atmosphere and diminishes the convection and thus the potential for cloud formation, (2) increasing the atmospheric temperature, which reduces the relative humidity, inhibits cloud formation, and enhances evaporation of existing clouds. This is collectively termed the semi-direct aerosol effect (Hansen et al. 1997). The net effect is uncertain (see Figure 3b) and highly depends on the vertical profile of BC (Koch & Del Genio 2010). In addition, BC and other absorbing aerosols deposited on snow or ice surfaces may reduce the surface albedo, leading to reduced reflectance of solar radiation, and hence a heating effect (Hansen & Nazarenko 2004). Radiative forcing (RF) is often used to quantify and compare the potential climate impact of the various aerosol effects. RF is defined as a change in the Earth's radiation balance due to a perturbation of anthropogenic or natural origin.. The total aerosol forcing probability density function (PDF), in addition to individual aerosol components, indicating both the magnitudes and uncertainty of the effects, is shown in Figure 4a. The wider a PDF, the larger is the uncertainty. Combining all aerosol effects (blue dashed curve in Figure 4a) enhances the uncertainty compared to considering only the direct aerosol effect and cloud albedo effect.

Aerosol examples

Andrews, E. et al. Climatology of aerosol radiative properties in the free troposphere. Atmospheric Research 102, 365-393 (2011).

Jones, A. et al. A climate model study of indirect radiative forcing by anthropogenic sulfate aerosols. Nature 370, 450-453 (1994).

What are aerosols in the atmosphere

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Hansen, J. & Nazarenko, L. Soot climate forcing via snow and ice albedos. Proceedings of the National Academy Of Sciences (USA) 101, 423-428 (2004).

Novakov, T. et al. Airborne measurements of carbonaceous aerosols on the East Coast of the United States. Journal of Geophysical Research-Atmospheres 102, 30023-30030 (1997).

Fullerton, D. G. et al. Biomass fuel use and indoor air pollution in homes in Malawi. Occupational and Environmental Medicine 66, 777-783 (2009).

Forster, P. et al. Changes in Atmospheric Constituents and in Radiative Forcing, Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK: Cambridge University Press, 2007.

Quinn, P. K. & Bates, T. S. Regional aerosol properties: Comparisons of boundary layer measurements from ACE 1, ACE 2, aerosols99, INDOEX, ACE asia, TARFOX, and NEAQS. Journal of Geophysical Research-Atmospheres 110, D14202 (2005).

Myhre, G. et al. Modelled radiative forcing of the direct aerosol effect with multi-observation evaluation. Atmospheric Chemistry and Physics 9, 1365-1392 (2009).

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