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- ItemMaritime aerosol network as a component of AERONET - First results and comparison with global aerosol models and satellite retrievals(München : European Geopyhsical Union, 2011) Smirnov, A.; Holben, B.N.; Giles, D.M.; Slutsker, I.; O'Neill, N.T.; Eck, T.F.; Macke, A.; Croot, P.; Courcoux, Y.; Sakerin, S.M.; Smyth, T.J.; Zielinski, T.; Zibordi, G.; Goes, J.I.; Harvey, M.J.; Quinn, P.K.; Nelson, N.B.; Radionov, V.F.; Duarte, C.M.; Losno, R.; Sciare, J.; Voss, K.J.; Kinne, S.; Nalli, N.R.; Joseph, E.; Krishna Moorthy, K.; Covert, D.S.; Gulev, S.K.; Milinevsky, G.; Larouche, P.; Belanger, S.; Horne, E.; Chin, M.; Remer, L.A.; Kahn, R.A.; Reid, J.S.; Schulz, M.; Heald, C.L.; Zhang, J.; Lapina, K.; Kleidman, R.G.; Griesfeller, J.; Gaitley, B.J.; Tan, Q.; Diehl, T.L.The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. Over 80 cruises were completed through early 2010 with deployments continuing. Measurement areas included various parts of the Atlantic Ocean, the Northern and Southern Pacific Ocean, the South Indian Ocean, the Southern Ocean, the Arctic Ocean and inland seas. MAN deploys Microtops hand-held sunphotometers and utilizes a calibration procedure and data processing traceable to AERONET. Data collection included areas that previously had no aerosol optical depth (AOD) coverage at all, particularly vast areas of the Southern Ocean. The MAN data archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we present results of AOD measurements over the oceans, and make a comparison with satellite AOD retrievals and model simulations.
- ItemAerosol number size distributions from 3 to 500 nm diameter in the arctic marine boundary layer during summer and autumn(Copenhagen : Blackwell Munksgaard, 1996) Covert, D.S.; Wiedensohler, A.; Aalto, P.; Heintzenberg, J.; Mcmurry, P.H.; Leck, C.Aerosol physics measurements made onboard the Swedish icebreaker Oden in the late Summer and early Autumn of 1991 during the International Arctic Ocean Expedition (IAOE-91) have provided the first data on the size distribution of particles in the Arctic marine boundary layer (MBL) that cover both the number and mass modes of the size range from 3 to 500 nm diameter. These measurements were made in conjunction with atmospheric gas and condensed phase chemistry measurements in an effort to understand a part of the ocean-atmosphere sulfur cycle. Analysis of the particle physics data showed that there were three distinct number modes in the submicrometric aerosol in the Arctic MBL. These modes had geometric mean diameters of around 170 nm. 45 nm and 14 nm referred to as accumulation, Aitken and ultrafine modes, respectively. There were clear minima in number concentrations between the modes that appeared at 20 to 30 nm and at 80 to 100 nm. The total number concentration was most frequently between 30 and 60 particles cm-3 with a mean value of around 100 particles cm-3, but the hourly average concentration varied over two to three orders of magnitude during the 70 days of the expedition. On average, the highest concentration was in the accumulation mode that contained about 45% of the total number, while the Aitken mode contained about 40%. The greatest variability was in the ultrafine mode concentration which is indicative of active, earby sources (nucleation from the gas phase) and sinks; the Aitken and accumulation mode concentrations were much less variable. The ultrafine mode was observed about two thirds of the time and was dominant 10% of the time. A detailed description and statistical analysis of the modal aerosol parameters is presented here.
- ItemA comparison of aerosol chemical and optical properties from the 1st and 2nd Aerosol Characterization Experiments(Milton Park : Taylor & Francis, 2016) Quinn, P.K.; Bates, T.S.; Coffman, D.J.; Coffman, Derek J.; Miller, T.L.; Johnson, J.E.; Covert, D.S.; Putaud, J.- P.; Neusüß, C.; Novakov, T.Shipboard measurements of aerosol chemical composition and optical properties were made during both ACE-1 and ACE-2. ACE-1 focused on remote marine aerosol minimally perturbed by continental sources. ACE-2 studied the outflow of European aerosol into the NE Atlantic atmosphere. A variety of air masses were sampled during ACE-2 including Atlantic, polar, Iberian Peninsula, Mediterranean, and Western European. Reported here are mass size distributions of non-sea salt (nss) sulfate, sea salt, and methanesulfonate and submicron and supermicron concentrations of black and organic carbon. Optical parameters include submicron and supermicron aerosol scattering and backscattering coefficients at 550 nm, the absorption coefficient at 550±20 nm, the Ångström exponent for the 550 and 700 nm wavelength pair, and single scattering albedo at 550 nm. All data are reported at the measurement relative humidity of 55%. Measured concentrations of nss sulfate aerosol indicate that, relative to ACE-1, ACE-2 aerosol during both marine and continental flow was impacted by continental sources. Thus, while sea salt controlled the aerosol chemical composition and optical properties of both the submicron and supermicron aerosol during ACE-1, it played a relatively smaller role in ACE-2. This is confirmed by the larger average Ångström exponent for ACE-2 continental aerosol of 1.2±0.26 compared to the ACE-1 average of -0.03±0.38. The depletion of chloride from sea salt aerosol in ACE-2 continental air masses averaged 55±25% over all particle sizes. This compares to the ACE-2 marine average of 4.8±18% and indicates the enhanced interaction of anthropogenic acids with sea salt as continental air masses are transported into the marine atmosphere. Single scattering albedos averaged 0.95±0.03 for ACE-2 continental air masses. Averages for ACE-2 and ACE-1 marine air masses were 0.98±0.01 and 0.99±0.01, respectively.
- ItemOverview of the atmospheric research program during the International Arctic Ocean Expedition of 1991 (IAOE-91) and its scientific results(Milton Park : Taylor & Francis, 2017) Leck, C.; Bigg, E.K.; Covert, D.S.; Heintzenberg, J.; Maenhaut, W.; Nilsson, E.D.; Wiedensohler, A.The broad aim of the Atmospheric program of the International Arctic Ocean Expedition (IAOE-91) was to test the hypothesis that marine biogenically produced dimethyl sulfide (DMS) gas can exert a significant global climatic control. The hypothesis states that DMS is transferred to the atmosphere and is oxidised to form airborne particles. Some of these grow large enough to act as cloud condensation nuclei (CCN) which help determine cloud droplet concentration. The latter has a strong influence on cloud albedo and hence on the radiation balance of the area affected. In summer, the central Arctic is a specially favourable region for studying the natural sulfur cycle in that the open waters surrounding the pack ice are the only significant sources of DMS and there are almost no anthropogenic particle sources. Concentrations of seawater and atmospheric DMS decreased at about the same rate during the period of measurements, (1 August to 6 October, latitudes 75°N to 90°N) spanning about three orders of magnitude. Methane sulfonate and nonsea salt sulfate in the submicrometer particles, which may be derived from atmospheric DMS, also decreased similarly, suggesting that the first part of the hypothesis under test was true. Influences on cloud droplet concentration and radiation balance could not be measured. Size-resolved aerosol chemistry showed a much lower proportion of methane sulfonate to be associated with supermicrometer particles than has been found elsewhere. Its molar ratio to nonsea salt sulfate suggested that the processes controlling the particulate chemistry do not exhibit a net temperature dependence. Elemental analysis of the aerosol also revealed the interesting possibility that debris from Siberian rivers transported on the moving ice represent a fairly widespread source of supermicrometer crustal material within the pack ice. Highly resolved measurements of aerosol number size distributions were made in the diameter range 3 nm to 500 nm. 3 distinct modal sizes were usually present, the “ultrafine”, “Aitken” and “accumulation” modes centred on 14, 45 and 170 nm diameter, respectively. The presence of ultrafine particles, implying recent production, was more frequent than has been found in lower latitude remote marine areas. Evidence suggests that they were mixed to the surface from higher levels. Sudden and often drastic changes in aerosol concentration and size distribution were surprisingly frequent in view of the relatively slowly changing meteorology of the central Arctic during the study period and the absence of strong pollution sources. They were most common in particles likely to have taken part in cloud formation (> 80 nm diameter). 2 factors appear to have been involved in these sudden changes. The 1st was the formation of vertical gradients in aerosol concentration due to interactions between particles and clouds or favoured regions for new particle production during periods of stability. The 2nd was sporadic localised breakdowns of the stability, bringing changed particle concentrations to the measurement level. Probable reasons for these sporadic mixing events were indicated by the structure of the Marine Boundary Layer (MBL) investigated with high resolution rawinsondes. Low level jets were present about 60% of the time, producing conditions conductive to turbulence and shear-induced waves. It is concluded that an even more detailed study of meteorological processes in the MBL in conjunction with more highly time-resolved measurements of gas-aerosol physics and chemistry appears to be essential in any future research aimed at studying the indirect, cloud mediated, effect of aerosol particles.
- ItemSize-segregated chemical, gravimetric and number distribution-derived mass closure of the aerosol in Sagres, Portugal during ACE-2(Milton Park : Taylor & Francis, 2016) Neusüß, C.; Weise, D.; Birmili, W.; Wex, H.; Wiedensohler, A.; Covert, D.S.During the ACE-2 field campaign in the summer of 1997 an intensive, ground-based physical and chemical characterisation of the clean marine and continentally polluted aerosol was performed at Sagres, Portugal. Number size distributions of the dry aerosol in the size range 3–10 000 nm were continuously measured using DMPS and APS systems. Impactor samples were regularly taken at 60% relative humidity (RH) to obtain mass size distributions by weighing the impactor foils, and to derive a chemical mass balance by ion and carbon analysis. Hygroscopic growth factors of the metastable aerosol at 60% RH were determined to estimate the number size distribution at a relative humidity of 60%. A size segregated 3-way mass closure study was performed in this investigation for the first time. Mass size distributions at 60% RH derived from number size distribution measurements and impactors samples (weighing and chemical analysis) are compared. A good agreement was found for the comparison of total gravimetrically-determined mass with both number distribution-derived (slope=1.23/1.09; R2>0.97; depending on the parameters humidity growth and density) and chemical mass concentration (slope=1.02; R2=0.79) for particles smaller than 3 mm in diameter. Except for the smallest impactor size range relatively good correlations (slope=0.86–1.42) with small deviations (R2=0.76–0.98) for the different size fractions were found. Since uncertainties in each of the 3 methods are about 20% the observed differences in the size-segregated mass fractions can be explained by the measurement uncertainties. However, the number distributionderived mass is mostly higher than the chemically and gravimetrically determined mass, which can be explained by sampling losses of the impactor, but as well with measurement uncertainties as, e.g., the sizing of the DMPS/APS.