BADC Doc: Research Achievements of the NAMBLEX Experiment
Source: environment.data.gov.uk (2018-06-19)

NAMBLEX - North Atlantic Marine Boundary Layer EXperiment  dataset collection: chemical and meteorological atmospheric measurements. The North Atlantic Marine Boundary Layer EXperiment (NAMBLEX) campaign was an atmospheric composition campaign conducted at Mace Head in Ireland from 24 July 2002 to 3 September 2002. The data consist of chemical and meteorological atmospheric measurements, model data and trajectories from a number of instruments, including several from the Universities Facility for Atmospheric Measurements (UFAM). The chemical species measured includes: O3, CO, H2, DMS, CH4, NMHC, NOx, NOy, PAN, VOCs, HCHO, peroxides, organo-halogenated species, a range of shorter lived halogen species (I2, OIO, IO, BrO), NO3 radicals, photolysis frequencies, and the free radicals OH, HO2 and (HO2 + Σ RO2). The BADC is the primary archiving and distribution data centre for NAMBLEX.

Research Achievements of the North Atlantic Marine Boundary Layer Experiment (NAMBLEX)

Introduction

The NAMBLEX consortium consists of the following institutions: The Universities of Aberystwyth, Birmingham, Bristol, Cambridge, Edinburgh, Leeds, Leicester, Manchester Institute of Science and Technology, Reading, East Anglia, York, Imperial College of Science, Technology and Medicine, and the National University of Ireland at Galway. In addition scientists from TNO, Holland, and the British Antarctic Survey participated in the campaign, that took place over 7 weeks in the summer of 2002 (July 23 - September 7, 2002), at the Mace Head Atmospheric Research Station, Ireland. The site is operated by the National University of Ireland, Galway, and the University of Bristol. More than 50 NERC-funded scientists were involved in the campaign (with a further 20 visiting). NAMBLEX represented perhaps the most detailed compositional study of the marine boundary layer, and deployed a wide range of instrumentation for the measurement of gaseous trace gases and aerosols, in some cases for the first time, several funded through the Universities Facility for Atmospheric Measurements (UFAM) Joint Infrastructure Fund award. Five instrumented shipping containers were deployed together at the shore site at Mace Head.

Achievements of the field campaign

Chemical and dynamical measurements. Chemists, physicists and meteorologists worked together during NAMBLEX. Detailed chemical compositional measurements ran alongside detailed physical measurements of the structure of the boundary layer. Events where the local flow is decoupled from the synoptic flow were identified from physical measurements (balloon, SODAR, wind profiler, sonic anemometers). This is crucial for interpretation of chemical data.

New molecules measured. First measurements of I2 and mid-latitude measurements of BrO. First measurements of OIO using broad-band cavity ring-down spectroscopy. Determination of NO3 using two methods - long path and in situ. Highly detailed speciation of oxygenated VOCs using several instruments, measured continuously during the campaign.

New instruments deployed. A number of new instruments, funded mainly through NERC, were deployed, including a wind profiler, two aerosol mass spectrometers, upgraded FAGE and DOAS instruments, two CH2O instruments, two peroxide instruments, a negative ion mass spectrometer for alkyl nitrates, speciated hydrocarbons and oxygenated VOCs using several GCS, a new broad-band cavity ring-down spectrometer, and a new MAX-DOAS instrument.

Comprehensive data sets during clean westerlies. Clean westerly trajectories were encountered over several weeks. Comprehensive measurements of many species, including NMHC, halogen precursors using GC-MS, o-VOCs, free-radicals (OH, HO2, RO2, NO3, IO), and a wide range of supporting measurements of free-radical sources and sinks.

Real time aerosol composition as a function of aerosol diameter using two complementary mass spectrometry methods (Aerodyne AMS and TSI ATOFMS), single particle analysis. Real time size/number distributions, coupled with growth factors (hygroscopicity) enables a realistic reactive surface area to be calculated and CCN activity to be evaluated.

Role of halogens in controlling the HOX budget. Coupling of HOx/XOx cycles clearly demonstrated in the troposphere (only demonstrated before in the stratosphere). Up to 40% of HO2 loss is controlled by reaction with IO at low tide.

Role of iodine in production of new particles in the MBL. Co-measurements of organic iodine compounds (using GC-MS), radical intermediates (IO, OIO), and I2, and measurement of aerosol phase iodine has aided the understanding of the formation of new particles in the marine environment, which can grow to CCN. Halogens are present in small particles formed from the interaction of seaweed with ozone/UV light. Model of aerosol nucleation developed.

Model comparisons - importance of oxygenates and halogens. Comparison of measurements of OH, HO2 and RO2 with predictions of box model based on the Master Chemical Mechanism. Modelled and measured HOx and ROx in much better agreement than previously observed at Mace Head, and better if oxygenated species (e.g. alcohols, acetylaldehye and acetone) included as sinks for OH. O-VOCs not measured before in the MBL under clean conditions. There are significant concentrations of HO2 and total peroxy radicals at night, in good agreement with the model

Intercomparisons. For some species, e.g. CH2O, peroxides, NMHC, measurements were made using more than one technique, enabling comparison of methods. In most cases agreement was excellent, enabling validation of instruments.

Summary
- The agreement between measured/MCM modelled concentrations of OH, HO2 and total peroxy radicals is good and much better than in previous campaigns at Mace Head. Halogens required to adequately describe the HOx chemistry.
- Excellent speciation of VOCs. Previously unmeasured oxygenated compounds have a significant effect on OH. O-VOCS appear mainly to have been generated during long-range transport, and the ocean shown to be a sink for methanol.
- I2 photolysis is the dominant source of iodine radicals. Evidence that the reaction I2+NO3 may provide a source of IO at night. First measurements of mid-latitude BrO, generated as a result of IBr photolysis produced from sea-salt aerosol.
- Aerosols ? novel composition measurements using two instruments, realistic surface areas. Very large data sets.
- Chemists and physicists have worked together. Intercomparisons and sharing of standards have improved instruments.