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Sources of nitrate in stratocumulus cloud water: Airborne measurements during the 2011 E-PEACE and 2013 NiCE studies

Prabhakar, Gouri and Ervens, B. and Wang, Z. and Maudlin, L. C. and Coggon, M. M. and Jonsson, H. H. and Seinfeld, J. H. and Sorooshian, A. (2014) Sources of nitrate in stratocumulus cloud water: Airborne measurements during the 2011 E-PEACE and 2013 NiCE studies. Atmospheric Environment, 97 . pp. 166-173. ISSN 1352-2310.

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This study examines the sources of NO_3^− 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 NO_3^− air-equivalent concentrations in cloud water samples categorized as having been influenced by ship exhaust (2.5 μg m^(−3)), strong marine emissions (2.5 μg m^(−3)) and fires (2.0 μg m^(−3)) were more than twice that in the background cloud water (0.9 μg m^(−3)). 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 NO_3^− levels reaching as high as 9.0 μg m^(−3). Nucleation scavenging of chloride depleted sea-salt is a source of cloud water NO^3^−, with the lowest Cl^−:Na^+ ratio (1.5) observed in ship-influenced samples. Surface aerosol measurements show that NO_3^− concentrations peak in the particle diameter range of 1.0–5.6 μm, similar to Na, Cl^− and Si, suggesting that drop activation of crustal particles and sea salt could be an important source of NO_3^− in cloud water. The contrasting behavior of NO_3^− and SO_4^(2−) is emphasized by the NO_3^−:SO_4^(2−) 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 NO_3^−:SO_4^(2−) ratio with altitude in clouds are confirmed by parcel model studies due to the higher rate of in-cloud sulfate formation as compared to HNO_3 uptake by droplets.

Item Type:Article
Related URLs:
URLURL TypeDescription
Wang, Z.0000-0002-7921-3134
Coggon, M. M.0000-0002-5763-1925
Jonsson, H. H.0000-0003-3043-1074
Seinfeld, J. H.0000-0003-1344-4068
Sorooshian, A.0000-0002-2243-2264
Additional Information:© 2014 Elsevier Ltd. Received 18 March 2014. Received in revised form 6 August 2014. Accepted 8 August 2014. Available online 9 August 2014. This work was funded by Office of Naval Research grants N00014-11-1-0783, N00014-10-1-0200, and N00014-10-1-0811, and National Science Foundation grant AGS-1008848. We acknowledge Dean Hegg for providing the cloud water collector. Barbara Ervens acknowledges support from NOAA's Climate Goal.
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-11-1-0783
Office of Naval Research (ONR)N00014-10-1-0200
Office of Naval Research (ONR)N00014-10-1-0811
National Oceanic and Atmospheric Administration (NOAA)UNSPECIFIED
Subject Keywords:Cloud water; Chloride depletion; Stratocumulus; Marine; Biomass burning; Sea-salt
Record Number:CaltechAUTHORS:20141118-070255543
Persistent URL:
Official Citation:Gouri Prabhakar, B. Ervens, Z. Wang, L.C. Maudlin, M.M. Coggon, H.H. Jonsson, J.H. Seinfeld, A. Sorooshian, Sources of nitrate in stratocumulus cloud water: Airborne measurements during the 2011 E-PEACE and 2013 NiCE studies, Atmospheric Environment, Volume 97, November 2014, Pages 166-173, ISSN 1352-2310, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:51876
Deposited By: Ruth Sustaita
Deposited On:18 Nov 2014 17:06
Last Modified:09 Mar 2020 13:19

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