Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption; influence on liquid, mixed phase, and ice clouds; and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr−1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models and should be increased by a factor of almost 3. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m−2 with 90% uncertainty bounds of (+0.08, +1.27) W m−2. Total direct forcing by all black carbon sources, without subtracting the preindustrial background, is estimated as +0.88 (+0.17, +1.48) W m−2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m−2 with 90% uncertainty bounds of +0.17 to +2.1 W m−2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m−2, is the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of short-lived co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil fuel and biofuel) have an industrial-era climate forcing of +0.22 (−0.50 to +1.08) W m−2 during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all short-lived emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all short-lived species from black-carbon-rich sources becomes slightly negative (−0.06 W m−2 with 90% uncertainty bounds of −1.45 to +1.29 W m−2). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.

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Bounding the role of black carbon in the climate system: A scientific assessment

Rapid industrialization and urbanization in developing countries has led to an increase in air pollution, along a similar trajectory to that previously experienced by the developed nations. In China, particulate pollution is a serious environmental problem that is influencing air quality, regional and global climates, and human health. In response to the extremely severe and persistent haze pollution experienced by about 800 million people during the first quarter of 2013 (refs 4, 5), the Chinese State Council announced its aim to reduce concentrations of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 micrometres) by up to 25 per cent relative to 2012 levels by 2017 (ref. 6). Such efforts however require elucidation of the factors governing the abundance and composition of PM2.5, which remain poorly constrained in China. Here we combine a comprehensive set of novel and state-of-the-art offline analytical approaches and statistical techniques to investigate the chemical nature and sources of particulate matter at urban locations in Beijing, Shanghai, Guangzhou and Xi'an during January 2013. We find that the severe haze pollution event was driven to a large extent by secondary aerosol formation, which contributed 30-77 per cent and 44-71 per cent (average for all four cities) of PM2.5 and of organic aerosol, respectively. On average, the contribution of secondary organic aerosol (SOA) and secondary inorganic aerosol (SIA) are found to be of similar importance (SOA/SIA ratios range from 0.6 to 1.4). Our results suggest that, in addition to mitigating primary particulate emissions, reducing the emissions of secondary aerosol precursors from, for example, fossil fuel combustion and biomass burning is likely to be important for controlling China's PM2.5 levels and for reducing the environmental, economic and health impacts resulting from particulate pollution.

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High secondary aerosol contribution to particulate pollution during haze events in China

Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed.

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The formation, properties and impact of secondary organic aerosol: current and emerging issues

Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

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Evolution of Organic Aerosols in the Atmosphere

Organic aerosol (OA) data acquired by the Aerosol Mass Spectrometer (AMS) in 37 field campaigns were deconvolved into hydrocarbon-like OA (HOA) and several types of oxygenated OA (OOA) components. HOA has been linked to primary combustion emissions (mainly from fossil fuel) and other primary sources such as meat cooking. OOA is ubiquitous in various atmospheric environments, on average accounting for 64%, 83% and 95% of the total OA in urban, urban downwind, and rural/remote sites, respectively. A case study analysis of a rural site shows that the OOA concentration is much greater than the advected HOA, indicating that HOA oxidation is not an important source of OOA, and that OOA increases are mainly due to SOA. Most global models lack an explicit representation of SOA which may lead to significant biases in the magnitude, spatial and temporal distributions of OA, and in aerosol hygroscopic properties.

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Ubiquity and dominance of oxygenated species in organic aerosols in anthropogenically-influenced Northern Hemisphere midlatitudes

31 The high atmospheric concentrations of toxic gases, particulate matter, and acids in the areas 32 immediately surrounding volcanoes can have negative impacts on human and ecological health. 33 In order to better understand the atmospheric fate of volcanogenic emissions in the near field (in 34 the first few hours after emission), we have carried out real-time measurements of key chemical 35 components of the volcanic plume from Kīlauea on the Island of Hawai‘i. Measurements were 36 made at two locations, one ~3 km north-northeast of the vent and the other 31 km to the 37 southwest, with sampling at each site spanning a range of meteorological conditions and volcanic 38 influence. Instrumentation included a sulfur dioxide monitor and an Aerosol Chemical 39 Speciation Monitor, allowing for a measurement of the partitioning between the two major sulfur 40 species (gas-phase SO2 and particulate sulfate) every 5 minutes. During trade wind conditions, 41 which sent the plume toward the southwest site, sulfur partitioning exhibited a clear diurnal 42 pattern, indicating photochemical oxidation of SO2 to sulfate; this enabled the quantitative 43 determination of plume age (5 hours) and instantaneous SO2 oxidation rate (2,4x10 -6 s -1 at solar 44 noon). Under stagnant conditions near the crater, the extent of SO2 oxidation was substantially 45 higher, suggesting faster oxidation. The particles within the plume were extremely acidic, with 46 pH values (controlled largely by ambient relative humidity) as low as -0.8 and strong acidity 47 (controlled largely by absolute sulfate levels) up to 2200 nmol/m 3 . The high variability of sulfur 48 partitioning and particle composition underscores the chemically dynamic nature of volcanic 49 plumes, which may have important implications for human and ecological health. 50

Atmospheric evolution of volcanic smog ("vog") from Kılauea: Real-time measurements of oxidation, dilution, and neutralization within a volcanic plume

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2. Measurements of fine particulate chemical composition in two U.K. cities

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Delta - atlanta hartsfield (una-una) study

A new aerosol collector for on-line analysis of particulate organic matter: the Aerosol Collection Module (ACM) T. Hohaus, D. Trimborn, A. Kiendler-Scharr, I. Gensch, W. Laumer, B. Kammer, S. Andres, H. Boudries, K. A. Smith, D. R. Worsnop, and J. T. Jayne Institut für Chemie und Dynamik der Geosphäre, ICG 2: Troposphäre, Forschungszentrum Jülich GmbH, Jülich, Germany Aerodyne Research Inc., Billerica, MA, USA Massachusetts Institute of Technology, Cambridge, MA, USA Received: 8 February 2010 – Accepted: 18 March 2010 – Published: 31 March 2010 Correspondence to: A. Kiendler-Scharr (a.kiendler-scharr@fz-juelich.de) Published by Copernicus Publications on behalf of the European Geosciences Union.

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John T. Jayne

Papers

Atmospheric evolution of volcanic smog ("vog") from Kılauea: Real-time measurements of oxidation, dilution, and neutralization within a volcanic plume

2. Measurements of fine particulate chemical composition in two U.K. cities

Delta - atlanta hartsfield (una-una) study

A new aerosol collector for on-line analysis of particulate organic matter: the Aerosol Collection Module (ACM)

Quantifying and improving the performance of the LaserAblation Aerosol Particle Time of Flight Mass Spectrometer(LAAPToF) instrument