Identification

Title

Observations of heterogeneous reactions between Asian pollution and mineral dust over the Eastern North Pacific during INTEX-B

Abstract

In-situ airborne measurements of trace gases, aerosol size distributions, chemistry and optical properties were conducted over Mexico and the Eastern North Pacific during MILAGRO and INTEX-B. Heterogeneous reactions between secondary aerosol precursor gases and mineral dust lead to sequestration of sulfur, nitrogen and chlorine in the supermicrometer particulate size range. Simultaneous measurements of aerosol size distributions and weak-acid soluble calcium result in an estimate of 11 wt% of CaCO₃ for Asian dust. During transport across the North Pacific, ~5–30% of the CaCO₃ is converted to CaSO₄ or Ca(NO₃)₂ with an additional ~4% consumed through reactions with HCl. The 1996 to 2008 record from the Mauna Loa Observatory confirm these findings, indicating that, on average, 19% of the CaCO₃ has reacted to form CaSO₄ and 7% has reacted to form Ca(NO3)2 and ~2% has reacted with HCl. In the nitrogen-oxide rich boundary layer near Mexico City up to 30% of the CaCO₃ has reacted to form Ca(NO₃)₂ while an additional 8% has reacted with HCl. These heterogeneous reactions can result in a ~3% increase in dust solubility which has an insignificant effect on their optical properties compared to their variability in-situ. However, competition between supermicrometer dust and submicrometer primary aerosol for condensing secondary aerosol species led to a 25% smaller number median diameter for the accumulation mode aerosol. A 10–25% reduction of accumulation mode number median diameter results in a 30–70% reduction in submicrometer light scattering at relative humidities in the 80–95% range. At 80% RH submicrometer light scattering is only reduced ~3% due to a higher mass fraction of hydrophobic refractory components in the dust-affected accumulation mode aerosol. Thus reducing the geometric mean diameter of the submicrometer aerosol has a much larger effect on aerosol optical properties than changes to the hygroscopic:hydrophobic mass fractions of the accumulation mode aerosol. In the presence of dust, nitric acid concentrations are reduced to <50% of total nitrate (nitric acid plus particulate nitrate). NOy as a fraction of total nitrogen (NOy plus particulate nitrate), is reduced from >85% to 60–80% in the presence of dust. These observations support previous model studies which predict irreversible sequestration of reactive nitrogen species through heterogeneous reactions with mineral dust during long-range transport.

Resource type

document

Resource locator

Unique resource identifier

code

http://n2t.net/ark:/85065/d7cr5vmf

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

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Text

originating controlled vocabulary

title

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reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

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East bounding longitude

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Temporal reference

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End position

Dataset reference date

date type

publication

effective date

2009-11-03T00:00:00Z

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Conformity

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Use constraints

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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

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