An overview of the Lagrangian experiments undertaken during the North Atlantic regional Aerosol Characterisation Experiment (ACE-2)

One of the primary aims of the North Atlantic regional Aerosol Characterisation Experiment (ACE-2) was to quantify the physical and chemical processes affecting the evolution of the major aerosol types over the North Atlantic. The best, practical way of doing this is in a Lagrangian framework where a parcel of air is sampled over several tens of hours and its physical and chemical properties are intensively measured. During the intensive observational phase of ACE-2, between 15 June 1997 and 24 July 1997, 3 cloudy Lagrangian experiments and 3 cloud-free, Lagrangian experiments were undertaken between the south west tip of the Iberian Peninsula and the Canary Islands. This paper gives an overview of the aims and logistics of all of the Lagrangian experiments and compares and contrasts them to provide a framework for the more focused Lagrangian papers in this issue and future process modelling studies and parametrisation development. The characteristics of the cloudy Lagrangian experiments were remarkably different, enabling a wide range of different physical and chemical processes to be studied. In the 1st Lagrangian, a clean maritime air mass was sampled in which salt particle production, due to increased wind speed, dominated the change in the accumulation mode concentrations. In the 2nd Lagrangian, extensive cloud cover resulted in cloud processing of the aerosol in a polluted air mass, and entrainment of air from the free troposphere influenced the overall decrease in aerosol concentrations in the marine boundary layer (MBL). Very little change in aerosol characteristics was measured in the 3rd Lagrangian, where the pollution in the MBL was continually being topped up by entraining air from a residual continental boundary layer (CBL) above. From the analysis of all the Lagrangian experiments, it has been possible to formulate, and present here, a generalised description of a European continental outbreak of pollution over the sub-tropical North Atlantic

Radical chemistry and ozone production at a UK coastal receptor site

OH, HO2, total and partially speciated RO2, and OH reactivity (kOH′) were measured during the July 2015 ICOZA (Integrated Chemistry of OZone in the Atmosphere) project that took place at a coastal site in north Norfolk, UK. Maximum measured daily OH, HO2 and total RO2 radical concentrations were in the range 2.6–17 × 106, 0.75–4.2 × 108 and 2.3–8.0 × 108 molec. cm−3, respectively. kOH′ ranged from 1.7 to 17.6 s−1, with a median value of 4.7 s−1. ICOZA data were split by wind direction to assess differences in the radical chemistry between air that had passed over the North Sea (NW–SE sectors) and that over major urban conurbations such as London (SW sector). A box model using the Master Chemical Mechanism (MCMv3.3.1) was in reasonable agreement with the OH measurements, but it overpredicted HO2 observations in NW–SE air in the afternoon by a factor of ∼ 2–3, although slightly better agreement was found for HO2 in SW air (factor of ∼ 1.4–2.0 underprediction). The box model severely underpredicted total RO2 observations in both NW–SE and SW air by factors of ∼ 8–9 on average. Measured radical and kOH′ levels and measurement–model ratios displayed strong dependences on NO mixing ratios, with the results suggesting that peroxy radical chemistry is not well understood under high-NOx conditions. The simultaneous measurement of OH, HO2, total RO2 and kOH′ was used to derive experimental (i.e. observationally determined) budgets for all radical species as well as total ROx (i.e. OH + HO2 + RO2). In NW–SE air, the ROx budget could be closed during the daytime within experimental uncertainty, but the rate of OH destruction exceeded the rate of OH production, and the rate of HO2 production greatly exceeded the rate of HO2 destruction, while the opposite was true for RO2. In SW air, the ROx budget analysis indicated missing daytime ROx sources, but the OH budget was balanced, and the same imbalances were found with the HO2 and RO2 budgets as in NW–SE air. For HO2 and RO2, the budget imbalances were most severe at high-NO mixing ratios, and the best agreement between HO2 and RO2 rates of production and destruction rates was found when the RO2 + NO rate coefficient was reduced by a factor of 5. A photostationary-steady-state (PSS) calculation underpredicted daytime OH in NW–SE air by ∼ 35 %, whereas agreement (∼ 15 %) was found within instrumental uncertainty (∼ 26 % at 2σ) in SW air. The rate of in situ ozone production (P(Ox)) was calculated from observations of ROx, NO and NO2 and compared to that calculated from MCM-modelled radical concentrations. The MCM-calculated P(Ox) significantly underpredicted the measurement-calculated P(Ox) in the morning, and the degree of underprediction was found to scale with NO.</p

Pacific Atmospheric Sulfur Experiment (PASE): dynamics and chemistry of the south Pacific tropical trade wind regime

The Pacific Atmospheric Sulfur Experiment (PASE) was a comprehensive airborne study of the chemistry and dynamics of the tropical trade wind regime (TWR) east of the island of Kiritibati (Christmas Island, 157º, 20′ W, 2º 52′ N). Christmas Island is located due south of Hawaii. Geographically it is in the northern hemisphere yet it is 6–12º south of the intertropical convergence zone (ITCZ) which places it in the southern hemisphere meteorologically. Christmas Island trade winds in August and September are from east south east at 3–15 ms−1. Clouds, if present, are fair weather cumulus located in the middle layer of the TWR which is frequently labeled the buffer layer (BuL). PASE provided clear support for the idea that small particles (80 nm) were subsiding into the tropical trade wind regime (TWR) where sulfur chemistry transformed them to larger particles. Sulfur chemistry promoted the growth of some of these particles until they were large enough to activate to cloud drops. This process, promoted by sulfur chemistry, can produce a cooling effect due to the increase in cloud droplet density and changes in cloud droplet size. These increases in particle size observed in PASE promote additional cooling due to direct scattering from the aerosol. These potential impacts on the radiation balance in the TWR are enhanced by the high solar irradiance and ocean albedo of the TWR. Finally because of the large area involved there is a large factional impact on earth’s radiation budget. The TWR region near Christmas Island appears to be similar to the TWR that persists in August and September, from southwest of the Galapagos to at least Christmas Island. Transport in the TWR between the Galapagos and Christmas involves very little precipitation which could have removed the aerosol thus explaining at least in part the high concentrations of CCN (≈300 at 0.5% supersaturation) observed in PASE. As expected the chemistry of sulfur in the trade winds was found to be initiated by the emission of DMS into the convective boundary layer (BL, the lowest of three layers). However, the efficiency with which this DMS is converted to SO2 has been brought into further question by this study. This unusual result has come about as result of our using two totally different approaches for addressing this long standing question. In the first approach, based on accepted kinetic rate constants and detailed steps for the oxidation of DMS reflecting detailed laboratory studies, a DMS to SO2 conversion efficiency of 60–73% was determined. This range of values lies well within the uncertainties of previous studies. However, using a completely different approach, involving a budget analysis, a conversion value of 100% was estimated. The latter value, to be consistent with all other sulfur studies, requires the existence of a completely independent sulfur source which would emit into the atmosphere at a source strength approximately half that measured for DMS under tropical Pacific conditions. At this time, however, there is no credible scientific observation that identifies what this source might be. Thus, the current study has opened for future scientific investigation the major question: is there yet another major tropical marine source of sulfur? Of equal importance, then, is the related question, is our global sulfur budget significantly in error due to the existence of an unknown marine source of sulfur? Pivotal to both questions may be gaining greater insight about the intermediate DMS oxidation species, DMSO, for which rather unusual measurements have been reported in previous marine sulfur studies. The 3 pptv bromine deficit observed in PASE must be lost over the lifetime of the aerosol which is a few days. This observation suggests that the primary BrO production rate is very small. However, considering the uncertainties in these observations and the possible importance of secondary production of bromine radicals through aerosol surface reactions, to completely rule out the importance of bromine chemistry under tropical conditions at this time cannot be justified. This point has been brought into focus from prior work that even at levels of 1 pptv, the effect of BrO oxidation on DMS can still be quite significant. Thus, as in the case of DMS conversion to SO2, future studies will be needed. In the latter case there will need to be a specific focus on halogen chemistry. Such studies clearly must involve specific measurements of radical species such as BrO

Development of a combined heart-cut and comprehensive two-dimensional gas chromatography system to extend the carbon range of volatile organic compounds analysis in a single instrument

The majority of atmospheric measurements of volatile organic compounds (VOCs) are usually limited to a small range, either in volatility or time resolution. A combined heart-cut gas chromatography (GC) with comprehensive two-dimensional GC (GC×GC) instrument was developed, specifically to increase the number of VOCs analysed using a single instrument. The system uses valve based modulation and was fully automated, making it suitable for use in the field. A laboratory comparison to an existing dual-channel GC (DC-GC) instrument demonstrated that this new GC-GC×GC can accurately measure atmospheric mixing ratios of C -C VOC species with a wide range of functionalities. Approximately hourly field measurements were conducted at a remote marine atmospheric research station in Bachok, Malaysia. This region was shown to be influenced by clean marine air masses, local anthropogenic and biogenic emission sources and aged emissions transported from highly polluted South East Asian regions. A dramatic shift in air mass direction was observed each day associated with the development of a sea breeze, which influenced the diurnal profiles of species measured at the Bachok site. A proton-transfer-reaction mass spectrometer (PTR-MS) was also deployed at Bachok and compared to the new GC-GC×GC instrument. Overall, the GC-GC×GC instrument has been shown to perform well in lab comparisons and during field observations. This represents a good compromise between volatility and high complexity measurements of VOCs

Pet Rodents and Fatal Lymphocytic Choriomeningitis in Transplant Patients

A unique strain of this virus was traced back to hamsters from an Ohio rodent distribution facility

Sensory Communication

Contains table of contents for Section 2, an introduction and reports on fifteen research projects.National Institutes of Health Grant RO1 DC00117National Institutes of Health Grant RO1 DC02032National Institutes of Health Contract P01-DC00361National Institutes of Health Contract N01-DC22402National Institutes of Health/National Institute on Deafness and Other Communication Disorders Grant 2 R01 DC00126National Institutes of Health Grant 2 R01 DC00270National Institutes of Health Contract N01 DC-5-2107National Institutes of Health Grant 2 R01 DC00100U.S. Navy - Office of Naval Research/Naval Air Warfare Center Contract N61339-94-C-0087U.S. Navy - Office of Naval Research/Naval Air Warfare Center Contract N61339-95-K-0014U.S. Navy - Office of Naval Research/Naval Air Warfare Center Grant N00014-93-1-1399U.S. Navy - Office of Naval Research/Naval Air Warfare Center Grant N00014-94-1-1079U.S. Navy - Office of Naval Research Subcontract 40167U.S. Navy - Office of Naval Research Grant N00014-92-J-1814National Institutes of Health Grant R01-NS33778U.S. Navy - Office of Naval Research Grant N00014-88-K-0604National Aeronautics and Space Administration Grant NCC 2-771U.S. Air Force - Office of Scientific Research Grant F49620-94-1-0236U.S. Air Force - Office of Scientific Research Agreement with Brandeis Universit

A year of H 2 measurements at Weybourne Atmospheric Observatory, UK

We present a year-long high precision time series of atmospheric molecular hydrogen (H2) measured at the UK North Sea coast from March 2008 to February 2009. We observed a pronounced seasonal cycle in H2 with mean values in late winter/early spring ~40 ppb higher than those in late summer/early autumn. Background-subtracted molar H2/CO ratios (&#x0394;H2/&#x0394;CO) averaged 0.35&#x00B1;0.002 for all data combined and 0.25&#x00B1;0.002 when &#x0394;H2 was above 10 ppb. The &#x0394;H2/&#x0394;CO ratio was highest in summer, possibly as a result of larger photochemical production. Using simultaneous measurements of ozone, we estimated the deposition velocity of H2 during nocturnal inversion events to average 3.5&#x00B1;0.7&#x00D7;10&#x2212;4 m s&#x2212;1 for June 2008 and 1.9&#x00B1;1&#x00D7;10&#x2212;4 m s&#x2212;1 for July 2008, in good agreement with other reported estimates. In May 2008, we observed an episode of exceptionally clean air being transported from the tropics but arriving from the north, in which H2 was slightly elevated indicating minimal surface loss. On another occasion with south-easterly winds, we believe we detected emissions from H2 production facilities in the near-continent characterised by H2 mixing ratios reaching 1450 ppb