RICO C-130 Gas Phase Hydrogen Peroxide and Methylhydroperoxide

Brian Heikes
Graduate School of Oceanography
University of Rhode Island
Narragansett,RI 02882-1197
USA

voice: 401.874.6638
fax: 401.874.6898
email: bheikes@gso.uri.edu


The gas phase peroxide data reported herein were obtained using the method described in Lee et al., 
J. Atmos. Ocean. Tech., 1995, flown on board the NCAR C-130 platform during the RICO, Rain in
Cumulus over the Ocean, experiment between December 3, 2004, and January 27, 2005, based out of 
Antigua.  Hydrogen peroxide is symbolically represented by H2O2.  Methylhydroperoxide is 
sympolically given by CH3OOHThe meausrements are given as molecular mixing ratios; molecules of 
specific gas per molecules of whole air times 1,000,000,000,000. or ppt-v.  The partial pressure 
of a specific gas can be calculated by:  P(H2O2) = MixingRatio(pptv) * P(air) /1,000,000,000,000.

The goal of RICO was a detailed understanding of rain formation in shallow "warm" cumulus clouds 
over the ocean.  Objectives included following the number density distributions and chemical 
evolution of aerosol, cloud condensation nuclei, cloud droplets, and precipitation.  Sulfur gas 
and partcile chemistry leading to sulfate was consider a key process and the measurements of 
peroxides are directly related to particulate sulfate formation. 

The peroxides are also relevant to the teasing about physical controls on the rain formation 
processes.  Peroxides are secondary chemical compounds produced within the atmosphere and may be 
simply considered the product of sunlight, ozone from aloft and water vapor below.  As such, 
their abundance reflects Free-troposphere/marine-boundary-layer material exchange and reaction.
Their abundance is related to air-to-sea surface deposition, precipitation scavenging, and in-
cloud reaction with sulfur dioxide.  The observations with other chemical and physical 
parameters and numerical chemical-transport modeling adds constraints to meteorological and 
cloud-physics interpretation of RICO resultss.

In situ air samples were continuously monitored.  Ambient air conatinung peroxides was brought 
intothe C-130 through a PFA teflon inlet heated to 35 C to prevent condensation.  The air stream
was then passed through an collection device, mixed with liguid water, peroxides scangened from 
the gas into solution with the spent air exhausted into the C-130 common dump line.  The inlet 
was located on the left side of the aircraft (10 o'clock position facing front) just forward of
the prop-line, extended approximately 16" off the skin of the aircraft into the free stream flow,
and roughly sampled normal to the air streamlines about the aircraft.

The aqueous collection solution was analyzed for hydrogen peroxide and methylhydroperoxide using 
the HPLC-fluorescence method above.  Primary calibrations of the HPLC system were done using 
dilute aqueous standards.  The air sample system used mass flow controllers to regulate sample 
flow and these were calibrated using NIST traceable volume flow calibration devices. Fluorescence 
blanks were determined by replacing the ambient air stream with Ultra-High purity air (Scott-
Marrin, Riverside CA).  Occasionally gas pase peroxide standards were introduced at the tip on the 
inlet to evaluate and confirm all peroxides entering inlet reached the collection device.

Stock aqueous peroxide standards were titrated against NIST traceable solutions before and after 
deployment.  A 20% degradation in hydrogen peroxide was observed and the stock standard was 
assumed to have decayed linearly over time.

The data files follow the ICARTT format, a modified NASA-GTE NOAA-AL data file format;
(http:/www-air.larc.nasa.gov/missions/intexna/DataManagement_plan.htm).  The file name provides
flight date and NCAR/RAF flight designator.  Data files are space delimited ASCII text format with
approximately 50 header records.  Each data record gives:
sample start time (in UTC seconds past mid-night on the day the flight took off), 
sample stop time (seconds as above), 
sample midpoint (seconds as above), 
hydrogen peroxide molecular mixing ratio (ppt, part per trillion by molecule), and 
methylhydroperoxide molecular mixing ratio (ppt).