Identification

Title

HOx chemistry during INTEX-A 2004: Observation, model calculation, and comparison with previous studies

Abstract

OH and HO₂ were measured with the Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) as part of a large measurement suite from the NASA DC-8 aircraft during the Intercontinental Chemical Transport Experiment-A (INTEX-A). This mission, which was conducted mainly over North America and the western Atlantic Ocean in summer 2004, was an excellent test of atmospheric oxidation chemistry. The HOx results from INTEX-A are compared to those from previous campaigns and to results for other related measurements from INTEX-A. Throughout the troposphere, observed OH was generally 0.95 of modeled OH; below 8 km, observed HO₂ was generally 1.20 of modeled HO₂. This observed-to-modeled comparison is similar to that for TRACE-P, another midlatitude study for which the median observed-to-modeled ratio was 1.08 for OH and 1.34 for HO₂, and to that for PEM-TB, a tropical study for which the median observed-to-modeled ratio was 1.17 for OH and 0.97 for HO₂. HO₂ behavior above 8 km was markedly different. The observed-to-modeled HO₂ ratio increased from ~1.2 at 8 km to ~3 at 11 km with the observed-to-modeled ratio correlating with NO. Above 8 km, the observed-to-modeled HO₂ and observed NO were both considerably greater than observations from previous campaigns. In addition, the observed-to-modeled HO₂/OH, which is sensitive to cycling reactions between OH and HO₂, increased from ~1.5 at 8 km to almost 3.5 at 11 km. These discrepancies suggest a large unknown HOx source and additional reactants that cycle HOx from OH to HO₂. In the continental planetary boundary layer, the observed-to-modeled OH ratio increased from 1 when isoprene was less than 0.1 ppbv to over 4 when isoprene was greater than 2 ppbv, suggesting that forests throughout the United States are emitting unknown HOx sources. Progress in resolving these discrepancies requires a focused research activity devoted to further examination of possible unknown OH sinks and HOx sources.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d7cf9q95

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

Keyword set

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

2008-03-08T00:00:00Z

Frequency of update

Quality and validity

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Conformity

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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