Sources of nitrate in stratocumulus cloud water: Airborne measurements during the 2011 E-PEACE and 2013 NiCE studies
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Authors
Prabhakar, Gouri
Ervens, B.
Wang, Z.
Maudlin, L.C.
Coggon, M.M.
Jonsson, H.H.
Seinfeld, J.H.
Sorooshian, A.
Subjects
cloud water
chloride depletion
stratocumulus
marine
biomass burning
sea-salt
chloride depletion
stratocumulus
marine
biomass burning
sea-salt
Advisors
Date of Issue
2014
Date
2014
Publisher
Elsevier Ltd.
Language
Abstract
This study examines the sources of NO₃ˉ
in stratocumulus clouds over the eastern Pacific Ocean off the
California coast using airborne and surface measurement data from the Eastern Pacific Emitted Aerosol
Cloud Experiment (E-PEACE; 2011) and Nucleation in California Experiment (NiCE; 2013). Average NO₃ˉ
air-equivalent concentrations in cloud water samples categorized as having been influenced by ship
exhaust (2.5 μg m ˉ³), strong marine emissions (2.5 μg m ˉ³) and fires (2.0 μg m ˉ³) were more than twice
that in the background cloud water (0.9 μg m ˉ³). During periods when biomass burning plumes resided
above cloud top, 16 of 29 cloud water samples were impacted due to instability in the entrainment
interface layer with NO₃ˉ
levels reaching as high as 9.0 μg m ˉ³. Nucleation scavenging of chloride
depleted sea-salt is a source of cloud water NO₃ˉ
, with the lowest Cl ˉ:Na⁺ ratio (1.5) observed in shipinfluenced
samples. Surface aerosol measurements show that NO₃ˉ
concentrations peak in the particle
diameter range of 1.0-5.6 μm, similar to Na, Cl ˉ and Si, suggesting that drop activation of crustal particles
and sea salt could be an important source of NO₃ˉ
in cloud water. The contrasting behavior of NO₃ˉ
and SO ²₄ˉ is emphasized by the NO₃ˉ
:SO ²₄ˉ mass concentration ratio which is highest in cloud water (by
more than a factor of two) followed by above cloud aerosol, droplet residual particles, and below cloud
aerosol. Trends of a decreasing NO₃ˉ
:SO ²₄ˉ ratio with altitude in clouds are confirmed by parcel model
studies due to the higher rate of in-cloud sulfate formation as compared to HNO₃ uptake by droplets.
Type
Article
Description
The article of record as published may be found at http://dx.doi.org/10.1016/j.atmosenv.2014.08.019
includes supplementary material
includes supplementary material
Series/Report No
Department
Organization
Naval Postgraduate School (U.S.)
Identifiers
NPS Report Number
Sponsors
Funder
Office of Naval Research grants N00014-11-1-0783, N00014-10-1-0200, and N00014-10-1-0811
National Science Foundation grant AGS-1008848
National Science Foundation grant AGS-1008848
Format
8 p.
Citation
Prabhakar, Gouri, et al. "Sources of nitrate in stratocumulus cloud water: Airborne measurements during the 2011 E-PEACE and 2013 NiCE studies." Atmospheric Environment 97 (2014): 166-173.
Distribution Statement
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.