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

Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

https://dspace.stir.ac.uk/bitstream/1893/30981/1/intcal20_northern_hemisphere_radiocarbon_age_calibration_curve_055_cal_kbp.pdf

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)

 The Lagrangian particle dispersion model FLEXPART was originally (about 8 years ago) designed for calculating the long-range and mesoscale dispersion of air pollutants from point sources, such as after an accident in a nuclear power plant In the meantime FLEXPART has evolved into a comprehensive tool for atmospheric transport modeling and analysis Its application fields were extended from air pollution studies to other topics where atmospheric transport plays a role (eg, exchange between the stratosphere and troposphere, or the global water cycle) It has evolved into a true community model that is now being used by at least 25 groups from 14 different countries and is seeing both operational and research applications A user manual has been kept actual over the years and was distributed over an internet page along with the model's source code In this note we provide a citeable technical description of FLEXPART's latest version (62)

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Technical note: The Lagrangian particle dispersion model FLEXPART version 6.2

There is growing evidence that the rate of warming is amplified with elevation, such that high-mountain environments experience more rapid changes in temperature than environments at lower elevations. Elevation-dependent warming (EDW) can accelerate the rate of change in mountain ecosystems, cryospheric systems, hydrological regimes and biodiversity. Here we review important mechanisms that contribute towards EDW: snow albedo and surface-based feedbacks; water vapour changes and latent heat release; surface water vapour and radiative flux changes; surface heat loss and temperature change; and aerosols. All lead to enhanced warming with elevation (or at a critical elevation), and it is believed that combinations of these mechanisms may account for contrasting regional patterns of EDW. We discuss future needs to increase knowledge of mountain temperature trends and their controlling mechanisms through improved observations, satellite-based remote sensing and model simulations.

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Elevation-dependent warming in mountain regions of the world

Organic carbon (OC) accounts for a large fraction of atmospheric aerosol and has profound effects on air quality, atmospheric chemistry and climate forcing. Molecular composition of the OC and its evolution during common processes of atmospheric aging have been a subject of extensive research over the last decade (see reviews of Ervens et al.,1 Hallquist et al.,2 Herckes et al.,3 Carlton et al.,4 Kroll and Seinfeld,5 Rudich et al.,6 and Kanakidou et al.7). Even though many fundamental advances have been reported in these studies, our understanding of the climate-related properties of atmospheric OC is still incomplete and the specific ways in which OC impacts atmospheric environment and climate forcing are just beginning to be understood. This review covers one topic of particular interest in this area –environmental chemistry of light-absorbing aerosol OC and its impact on radiative forcing.

Chemistry of atmospheric brown carbon.

In this paper we report a climatological analysis of nitrogen dioxide total column amounts at Mt. Cimone station 44/sup /spl deg// 11' N, 10/sup /spl deg// 42' E, 2165 m asl). Eight years of measurements obtained with the Gas Absorption Spectrometer Correlating Optical Differences (GASCOD) UV-Vis spectrometer are presented and a method based on the power spectrum analysis is proposed to investigate the nitrogen dioxide long term trend. This kind of diagnostic approach uses the geophysical phenomena (predictor) Identification in the frequency space to filter the time series from the natural induced oscillations. The advantage with respect to a statistical approach based on the correlation study between measurements and geophysical predictors is that only the identified phenomena are removed from the trend. On the other hand the effect of data missing in the filtering should be discussed and quantified in order to avoid misunderstanding in the results interpretation. Results show that a 7% increase per decade in the total column NO/sub 2/ is present at northern mid-latitudes.

Stratospheric NO/sub 2/ climatological trend at northern mid-latitudes from 8 years of ground based observations at Mt. Cimone Station

Variations in the concentration of surface ozone measured at a pollution-free mountain site from March 1991 to March 1992 are reported and discussed. Two of the ozone-transport episodes are presented in this case study: a stratospheric intrusion recorded in November 1991 and a horizontal transport in August 1991.

Episodes of vertical and horizontal ozone transport monitored at Italy's Mt. Cimone Observatory

A monitoring campaign of atmospheric pollutants was conducted in February 1993 by several of Italy's CNR institute in heavily polluted greater Milan. This metropolitan area, the largest one in northern Italy, is situated in the northernmost part of the Po Valley and, because of its topography and orography is frequently marked by low ventilation and inversion phenomena, a fast that promotes the accumulation and vertical layering over the city of pollutants. The need for more detailed information on air circulation and changes occurring in the lower atmospheric layers, as well as to understand why air-mass exchange does not take place, thereby impeding the dispersion of pollutants, was the project's goal- orientation. Measurement of NO2, SO2, O3, HNO2 were carried out over a 1.7 Km path in the city center by means of a DOAS system called GASCOD developed by remote sensing group of FISBAT-CNR at Bologna. The light source has been equipped with a remote-controlled occulting devices in order to separate the sky light scattered into the field of bye of the receiving system, which can interfere with the lamp spectra during daytime. The light from the source is collected by a Cassegrain telescope and focused on the spectrograph's entrance slit receiving system; the detector is a linear image sensor featuring an array of 512 MOS photodiodes. Data recorded in the same and boundary areas by a conventional analyzer from city's air-pollution monitoring network are reported for comparison. The statistical correlation of concentration values to the main weather and atmospheric stability parameters are stressed.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Measurements of atmospheric pollutants by a DOAS spectrometer in urban areas

The Mediterranean basin is characterized by elevated aerosol amounts and co-existence of different aerosol types, both natural and anthropogenic, while it is one of the most climatically sensitive areas. Therefore, it offers ideal conditions for studying aerosol processes and aerosol-climate interactions. An intensive aerosol physico-chemical characterization campaign was held at the Environmental-Climatic Observatory at Capo Granitola (Sicily; 37.5753◦ N, 12.6595◦ E) during April 2016, under the framework of the project Air-Sea Lab. The Observatory is located at the coast-line, facing the Strait of Sicily, and is part of the national I-AMICA network (http://www.i-amica.it/i-amica/?lang=en). Sub-micrometer aerosol chemical composition was measured by high resolution time of flight aerosol mass spectrometer (HR-ToF-AMS), for the first time at Capogranitola. Sea-salt concentration was estimated from AMS measurements following Ovadnevaite et al. (2012). For a complete mass closure of the submicron aerosol, black carbon (BC) concentration was derived from multiangle absorption photometer (MAAP) measurements. Positive matrix factorization was deployed to investigate organic aerosol (OA) sources at the site. Aerosol chemical composition confirms that Capogranitola is a representative background site, with generally low contribution of BC and nitrate and highly oxidized OA. In particular, aerosol sampled in the marine sector (130-310◦) is less affected by local sources and it is likely representative of the central Mediterranean background. Aerosol in background conditions is dominated by sulfate and OA (37% and 31%), followed by ammonium (12%), sea-salt (10%), BC (6%) and nitrate (3%). The average reconstructed sub-micrometer aerosol mass in background conditions is 3.7±2.3 μg m−3. OA source apportionment shows a minor contribution from primary sources, with hydrocarbon-like OA (HOA), from fossil fuel combustion, contributing for 3% and biomass burning OA (BBOA) for 2%. Oxidized OA (OOA) dominates the rest of OA mass. In particular, OOA1 and OOA2 (70% in total, OM:OC∼ 2.5) represent the result of prolonged atmospheric processing of OA, while OOA3 (25%, OM:OC ∼ 2.0) clearly represents fresher inputs of OOA from land. Investigation of HOA and BC time trends suggests that HOA in background conditions may be strongly contributed by ship traffic more than by land sources. The representativity of the background aerosol collected at Capogranitola will be discussed by comparing with measurements performed in parallel at the other I-AMICA southern Italy coastal stations and with those acquired in a subsequent cruise (May-June 2016) around the Italian Peninsula. Aerosol climate relevant properties, in relation with chemical composition, will be also presented and discussed.

Physico-chemical characterization of Mediterranean background aerosol at the Capogranitola observatory (Sicily)

Troposphere ozone concentration has been monitored since March 1991 at the Mt. Cimone Observatory (44 degree(s)12' N, 10 degree(s)42' E, 2165 m asl), a mountain site far from sources of anthropogenic pollution. The yearly trends of surface ozone concentration clearly evince a variation marked by peaks in spring and summer. That no ozone diurnal variations are usually found in late autumn, winter and early spring means that Mt. Cimone can be considered a baseline station over this period. In the warmer months, the daily ozone variation is affected by local mixing with the upwelling of ozone-poor low tropospheric air over the mid-daytime hours. Screening out the latter values, as well as those induced by horizontal transport phenomena from the pollutant-rich Po valley lowlands, yields free tropospheric ozone concentrations.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Paolo Bonasoni

Papers

Stratospheric NO/sub 2/ climatological trend at northern mid-latitudes from 8 years of ground based observations at Mt. Cimone Station

Episodes of vertical and horizontal ozone transport monitored at Italy's Mt. Cimone Observatory

Measurements of atmospheric pollutants by a DOAS spectrometer in urban areas

Physico-chemical characterization of Mediterranean background aerosol at the Capogranitola observatory (Sicily)

Surface ozone observations at Mt. Cimone Observatory, Italy