Identification

Title

Measurements of tropospheric HO₂ and RO₂ by oxygen dilution modulation and chemical ionization mass spectrometry

Abstract

An improved method for the measurement of hydroperoxy radicals (HO₂) and organic peroxy radicals (RO₂, where R is any organic group) has been developed that combines two previous chemical conversion/chemical ionization mass spectrometry (CIMS)peroxy radical measurement techniques. Applicable to both ground-based and aircraft platforms, the method provides good separation between HO₂ and RO₂ and frequent measurement capability with observations of both HO₂ and HO₂+RO₂ amounts each minute. This allows for analyses of measured [HO₂]/[HO₂+RO₂] ratios on timescales relevant to tropospheric photochemistry. By varying both [NO] and [O₂] simultaneously in the chemical conversion region of the PeRCIMS (Peroxy Radical CIMS) inlet, the method exploits the changing conversion efficiency of RO₂ to HO₂ under different inlet [NO]/[O₂] to selectively observe either primarily HO₂ or the sum of HO₂ and RO₂. Two modes of operation have been established for ambient measurements: in the ﬁrst half of the minute, RO2 radicals are measured at close to 100% efficiency along with HO₂ radicals (low [NO]/[O₂]=2.53×10-5) and in the second half of the minute, HO₂ is detected while the majority of ambient RO₂ radicals are measured with low efficiency, approximately 15% (high [NO]/[O₂]=6.80×10-4). The method has been tested extensively in the laboratory under various conditions and for a variety of organic peroxy radicals relevant to the atmosphere and the results of these tests are presented. The modified PeRCIMS instrument has been deployed successfully using the new measurement technique on a number of aircraft campaigns, including on the NSF/NCAR C-130 during the MIRAGE-Mex and NASA INTEX-B ﬁeld campaigns in the spring of 2006. A brief comparison of the peroxy radical measurements during these campaigns to a photochemical box model indicates good agreement under tropospheric conditions where NOx (NO+NO₂) concentrations are lower than 0.5 ppbV (parts per billion by volume).

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d76t0n4x

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

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keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

West bounding longitude

East bounding longitude

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Temporal reference

Temporal extent

Begin position

End position

Dataset reference date

date type

publication

effective date

2011-04-14T00:00:00Z

Frequency of update

Quality and validity

Lineage

Conformity

Data format

name of format

version of format

Constraints related to access and use

Constraint set

Use constraints

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

Metadata on metadata

Metadata point of contact