S. Fuzzi

Flood or Drought: How Do Aerosols Affect Precipitation?

Aerosols serve as cloud condensation nuclei (CCN) and thus have a substantial effect on cloud properties and the initiation of precipitation. Large concentrations of human-made aerosols have been reported to both decrease and increase rainfall as a result of their radiative and CCN activities. At one extreme, pristine tropical clouds with low CCN concentrations rain out too quickly to mature into long-lived clouds. On the other hand, heavily polluted clouds evaporate much of their water before precipitation can occur, if they can form at all given the reduced surface heating resulting from the aerosol haze layer. We propose a conceptual model that explains this apparent dichotomy.

Biogenically driven organic contribution to marine aerosol.

Marine aerosol contributes significantly to the global aerosol load and consequently has an important impact on both the Earths albedo and climate. So far, much of the focus on marine aerosol has centred on the production of aerosol from sea-salt and non-sea-salt sulphates. Recent field experiments, however, have shown that known aerosol production processes for inorganic species cannot account for the entire aerosol mass that occurs in submicrometre sizes. Several experimental studies have pointed to the presence of significant concentrations of organic matter in marine aerosol. There is some information available about the composition of organic matter, but the contribution of organic matter to marine aerosol, as a function of aerosol size, as well as its characterization as hydrophilic or hydrophobic, has been lacking. Here we measure the physical and chemical characteristics of submicrometre marine aerosol over the North Atlantic Ocean during plankton blooms progressing from spring through to autumn. We find that during bloom periods, the organic fraction dominates and contributes 63% to the submicrometre aerosol mass (about 45% is water-insoluble and about 18% water-soluble). In winter, when biological activity is at its lowest, the organic fraction decreases to 15%. Our model simulations indicate that organic matter can enhance the cloud droplet concentration by 15% to more than 100% and is therefore an important component of the aerosol–cloud–climate feedback system involving marine biota.

Cloud albedo enhancement by surface-active organic solutes in growing droplets

Understanding the properties of clouds in the Earths atmosphere is currently limited by difficulties at the fundamental level of adequately describing the processes of cloud droplet nucleation and growth. Small changes in droplet population may significantly influence cloud albedo as well as formation of precipitation. Models of cloud formation based on laboratory studies with idealized composition of nuclei suggest that organic solutes significantly lower surface tension—one of the parameters determining droplet population—but the lack of data on composition and properties of the organic material in the atmosphere precludes realistic laboratory or model studies. Here, we report measurements on vacuum-evaporated samples of cloud water from the Po Valley, Italy, that show a large decrease in surface tension, by up to about one-third relative to pure water, for realistic concentrations of organic solutes expected to exist in growing droplets. Such large surface-tension changes, if they occur in cloud droplets near the critical size for nucleation, lead to an increase in droplet population and hence in cloud albedo. The error produced in ignoring this effect is estimated to be comparable to other calculated direct and indirect influences of aerosols on scattering and absorption of solar radiation.

Inorganic, organic and macromolecular components of fine aerosol in different areas of Europe in relation to their water solubility

A chemical mass balance of fine aerosol (<1.5 μm AED) collected at three European sites was performed with reference to the water solubility of the different aerosol classes of components. The sampling sites are characterised by different pollution conditions and aerosol loading in the air. Aspvreten is a background site in central Sweden, K-puszta is a rural site in the Great Hungarian Plain and San Pietro Capofiume is located in the polluted Po Valley, northern Italy. The average fine aerosol mass concentration was 5.9 μg m-3 at the background site Aspvreten, 24 μg m-3 at the rural K-puszta and 38 μg m-3 at the polluted site San Pietro Capofiume. However, a similarly high soluble fraction of the aerosol (65–75%) was measured at the three sites, while the percentage of water soluble organic species with respect to the total soluble mass was much higher at the background site (ca. 50%) than at the other two sites (ca. 25%). A very high fraction (over 70%) of organic compounds in the aerosol consisted of polar species. The presence of water soluble macromolecular compounds was revealed in the samples from K-puszta and San Pietro Capofiume. At both sites these species accounted for between ca. 20–50% of the water soluble organic fraction. The origin of the compounds was tentatively attributed to biomass combustion.

Characterization of water‐soluble organic compounds in atmospheric aerosol: A new approach

A new methodological approach is proposed to characterize aerosol water-soluble organic compounds (WSOC). Real aerosol and fog water samples were subjected to a procedure based on a combination of Chromatographic separations, functional group investigation by proton nuclear magnetic resonance (HNMR), and total organic carbon determination. The complex mixture of aerosol/fog WSOC was separated by a Chromatographic procedure into three main classes of compounds: (1) neutral/basic compounds; (2) mono- and di-carboxylic acids; (3) polyacidic compounds. Characterization by HNMR spectroscopy showed that fraction 1 is mainly composed of polyols or polyethers, fraction 2 is mainly composed of hydroxylated aliphatic acidic compounds, while fraction 3 is composed of highly unsaturated polyacidic compounds of predominantly aliphatic character, with a minor content of hydroxyl- groups. Quantitative data on the three classes of compounds were then derived from total organic carbon analysis, showing that the three separated fractions together account for 77% (in terms of C) of the total WSOC concentration of a fog water sample. Further quantitative information on the functional groups present in the three separated fractions can be obtained from HNMR spectra. This newly proposed approach to aerosol WSOC characterization provides comprehensive and synthetic information on aerosol organic composition which can be helpful for modeling purposes and is also particularly useful when aerosol chemical mass closure is pursued.

Advances in characterization of size‐resolved organic matter in marine aerosol over the North Atlantic

0.80 m gm � 3 , the remainder being non-sea-salt (nss) sulphate, 0.03 ± 0.01 m gm � 3 , and nitrate, 0.13 ± 0.04 m gm � 3 . By comparison, the mass of sea salt, nss sulphate, and nitrate in the submicron mode is found to be 0.39 ± 0.08 m gm � 3 , 0.26 ± 0.04 m gm � 3 , and 0.02 ± 0.01 m gm � 3 , respectively. Water-soluble organic carbon (WSOC) is observed in the submicron mode with a mass concentration of 0.25 ± 0.04 m gm � 3 , comparable to that of nss sulphate, and in the supermicron mode with a mass concentration of 0.17 ± 0.04 m gm � 3 . The WSOC to total carbon (TC) ratio is found to be 0.20 ± 0.12 for the submicron fraction and 0.29 ± 0.08 for the supermicron fraction, while the black carbon (BC) to TC ratio is, on average, 0.032 ± 0.001 for both aerosol modes. The remaining carbon, water-insoluble organic carbon, contributes 0.66 ± 0.11 m gm � 3 and 0.26 ± 0.06 m gm � 3 to the submicron and supermicron modes, respectively and, thus, represents the dominant submicron aerosol species. Furthermore, the WSOC chemical composition comprises mainly aliphatic and only partially oxidized species and humiclike substances, resulting in appreciable surface-active properties. The observed organic matter chemical features (size-dependent concentration, hydrophobic nature of a substantial fraction of the organic matter, and low oxidized and surface-active WSOC species) are consistent with the hypothesis of a primary marine source; bubble-bursting processes, occurring at the surface of the North Atlantic Ocean during phytoplankton blooms, effectively transfer organic matter into marine aerosol particles, particularly enriching the fine-aerosol fraction. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry;

Primary submicron marine aerosol dominated by insoluble organic colloids and aggregates

The chemical properties of sea-spray aerosol particles produced by artificially generated bubbles using oceanic waters were investigated during a phytoplankton bloom in the North Atlantic. Spray pa ...

Surface tension of atmospheric wet aerosol and cloud/fog droplets in relation to their organic carbon content and chemical composition

A decrease in surface tension with respect to pure water was observed in wet aerosol and cloud/fog samples. The measured decrease of surface tension is positively correlated with the concentration of total soluble organic compounds in the samples. On the basis of a previously developed methodology to fractionate soluble organic compounds into three different classes (neutral compounds, mono- and dicarboxylic acids and polycarboxylic acids), we investigated the surface-active behaviour of the compounds within each of these classes. Polycarboxylic acids having a molecular structure analogous to that of humic substances (humic-like substances) were found to be the most effective surface-active species within the droplets: three times more effective than mono- and dicarboxylic acids and one order of magnitude more than neutral compounds.

Chemical features and seasonal variation of fine aerosol water-soluble organic compounds in the Po Valley, Italy

Abstract We present here an investigation on the annual cycle of the carbonaceous fraction of the Po Valley (Italy) fine (d

Water soluble organic compounds formed by oxidation of soot

The water soluble organic compounds (WSOC) in soot samples as a function of the extent of ozone oxidation have been measured by a new methodology which utilises ion exchange chromatography, total carbon analysis and proton nuclear magnetic resonance. These results have been compared with the same analyses of various atmospheric aerosol samples. The WSOC produced from oxidation of soot particles increase rapidly with ozone exposure and consist primarily of aromatic polyacids which are found widely in atmospheric aerosols and which are frequently referred to as macromolecular humic-like substances (HULIS). This work demonstrates that the atmospheric oxidation of soot can produce HULIS in aerosols. The cloud condensation nuclei effectiveness of soot aerosol likely has its origin in these oxidation processes.