Contents Welcome Core Measurements Instrumentation Data Processing and Analysis Tools Data Archive Contacts

Welcome to the Core Measurements for Field Programs website!   This project provides a core set of field measurements essential to field projects in ASP examining aerosol radiative forcing.  Research-grade instruments are operated on behalf of the program for aerosol precursors, atmospheric oxidants, aerosol microphysical properties, aerosol composition and ancillary trace gases.  This equipment has been field proven and meets the unique requirements of aircraft-based sampling, primarily aboard the DOE Research Aircraft Facility.  Multiple associated infrastructure activities are an important component of this project and include providing quality assurance, aircraft installation, trained operators, ‘first-look’ data in the field, final-data reduction and archival distribution of final-form results.  To meet the needs of Atmospheric Science Program (ASP) goals, the instrument systems are being expanded to encompass anticipated measurement capabilities as required by climate-related aerosol studies.  Return to top

 

Core Measurements Instrumentation

Oxides of Nitrogen:  Nitric oxide is a by-product of fossil-fuel combustion and, in the presence of sunlight and hydrocarbons acts as the catalyst for the formation of atmospheric ozone.  These photochemical processes produce nitric acid, which is the precursor to aerosol nitrate.  Thus, measurement of the oxides of nitrogen is important both from  the perspective of the  photochemistry leading to aerosol formation, but also to the formation of an important aerosol precursor.  We currently operate a three-channel, chemiluminescent-based, oxides of nitrogen detector, designed and constructed at BNL for use on aircraft.  The instrument simultaneously measures NO, NO₂ and the sum of odd-nitrogen species, NO_y.  This instrument provides 10-, 50-, and 200-pptv detection limits at 1-, 4- and 1-s integration times, respectively, for its three measurement channels.  In the current configuration, it does not measure nitric acid specifically, but NO_z, calculated as NO_y – (NO + NO₂), is a useful approximation under many conditions.  Calibration of instrument response is traceable to a NIST-certified, ‘primary’ NO standard.  NO₂ response is calibrated by quantitative titration of the gaseous NO standard.  Unit conversion of HNO₃ is verified for the NO_y channel.

Sulfur Dioxide:  A primary pollutant that forms sulfate aerosol when oxidized and the principal precursor  for anthropogenic aerosols.  Our instrument consists of an extensively modified commercial unit (TEI-43S) based on pulsed fluorescence detection.  At present, the instrument provides a ~200-pptv limit of quantitation and faster than 10-s response time.  In-flight stability is verified by periodic standard additions (traceable to NIST) in ambient air and chemical zeroes.

Ozone:  Ozone is the principal oxidant formed as a consequence of atmospheric  photochemistry.  Its photolysis is the principal source of the OH radical which, in turn, initiates the O₃ formation process.  The OH radical also directly reacts with a variety of trace substances in the atmosphere to form aerosols and aerosol precursors (e.g., with SO₂).  Several modified commercial analyzers that measure ozone by the UV-absorbance method are available.  These units have been modified for automatic zeroing and calibration during aircraft sampling.  These instruments have a 2-3 ppbv resolution and a 4-s time response.  Calibration procedures for ozone are traceable to the same NIST certified, ‘primary’ NO described above.

Peroxides:  Peroxides are the principal oxidant converting SO₂ to sulfate in clouds.  The ASP operates a three-channel instrument that continuously measures H₂O₂ and two organic peroxides in the gas phase.  A coil scrubber concentrates ambient samples in aqueous solution.  Peroxides are then determined by selective chemistry and fluorescence detection.  The time response is roughly 1-min with a ~60-pptv detection limit as operated aboard aircraft.

Carbon Monoxide:  Carbon  monoxide is a relatively long lived (~8 weeks) tracer of vehicular and biomass combustion processes (power plants normally produce little CO) and can be thus used to identify the contribution of aerosols and aerosol precursors from these sources.  CO measurements are provided from aircraft using a vacuum ultraviolet (VUV) fluorescence technique recently developed by Resonance Ltd. and tested at BNL.  This instrument has a 1-s response time with better than 4-ppbv resolution (compared with the previous method’s 30-s averaging and 20-30 ppbv resolution)!  In addition to providing high-resolution spatial mapping, this response speed is sufficient for the eddy-flux correlation method used to measure vertical fluxes of pollutants from aircraft.

Data Processing and Analysis Tools

During aircraft sampling, primary data from many real-time instruments are recorded as binary files (click here for details on the real-time data system).  Following each flight, researchers are supplied with ‘first look’ data sets within 1 hour.  The primary files are translated into ASCII files on a common time base using nominal calibration factors and can contain any combination of researcher-selected data streams.  These preliminary data sets serve multiple purposes including, verification of instrument operation, identification of unusual phenomena and aiding in subsequent mission planning.  Taking advantage of processing routines developed over the years, we are able to rapidly produce a variety of visualizations.  Some of these are shown below.

Time Series Data such as shown in the following figure,

when combined with the flight track, this information can be gridded to show the two-dimensional dispersion of emission sources:

Note the arrows are vectors of wind velocity measured in flight.

Particle size spectra can be flexibly displayed over time

as number, area or volume distributions from multiple sizing probes. Time series displays of the same data for the entire flight use color as a third dimension:

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Data Archive

Data from G-1 field campaigns are freely available to the research community at ftp://ftp.asd.bnl.gov/pub/ASP Field Programs/.  The file “READ ME.TXT” is updated to reflect the current status of each data set.  The file “File Guide.xls” contains a summary of all flight information (take-off and landing times, etc.).  Recently, graphic displays of each flight are presented as PDF files.  Data from the archive are made freely available, but appropriate inclusion of Principal Investigators (as co-authors or in the acknowlgement as appropriate) and acknowledgement of DOE/ASP is expected in any presentations and/or publications in accordance with the ASP data policy.

As of March 14, 2005, ftp://ftp.asd.bnl.gov/pub/ASP Field Programs/ is the primary location for data taken during ASP supported programs using the G-1 Research Aircraft Facility.  In the future, this location may change.  Data on the ftp site are 10-s averages.  1-s data is available on request as time permits.

The self-documenting structure of these files has been consistent since 1993. 

Conventions:

            1)         Files are named yymmddL_xx.txt where:

                        yy, mm, dd is the year, month and day (in UTC) of the date at take off. 

L is a letter begining at A and increments to differentiate between multiple flights on the same day.

xx denotes the time resolution of the data in seconds.

            2)         Date and Time are given in UTC.  Averaged data is, by definition, reported at the beginning of the averaging period.

            3)         Final processed data are reported in ASCII ‘flat files’ in PC/DOS conventions (tab delimited fields, CR/LF line termination).

            4)         The filename is in row 1 of each data column

The ‘last revision’ date is in row 7

Instrument descriptions are in rows 9-12

Comments on data or instrument operation are in rows 14-19

Constants used in processing (internal use mainly) are in rows 21-24

Statistics for each signal (n, min, max, avg) are in rows 26-30

Data titles are in row 35 and 36

Units are in row 37

Data start in row 40 and run uniformly to end of the file

            5)         All data have been time shifted (to the best of the P.I.’s ability) to reflect sampling time.

            6)         Integrated samples (such as filter packs or PILS measurements) are duplicated over all times corresponding to the sampling period.

            7)         Missing data are reported as empty fields (consecutive tab delimiters).

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Support Activities

For ground operations and to support Aircraft activities, a 34-foot mobile laboratory is made available.  The mobile laboratory is used to:

Transport equipment,

Conduct ground-based sampling,

Serve as a laboratory for ‘wet chemistry’ preparation,

Serve as a well-equipped base for instrument maintenance, repair and calibration, and

Provide office space for personnel.

In addition, a wireless LAN is provided along with limited network support for all program participants.

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Contacts

 

  This page was last updated 17Oct2006

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