Date of Award

Winter 1999

Project Type

Dissertation

Program or Major

Earth Sciences

Degree Name

Doctor of Philosophy

First Advisor

Robert W Talbot

Abstract

An intensive sampling program was carried out from May 1994 through November 1997 on the shore of the Gulf of Maine in New Castle, New Hampshire. Daily (24 hour averages) samples of bulk aerosol and gas phase HNO3, precipitation, and 20 aerosol size distributions were obtained. Particulate NH4+ and gas phase HNO3 were the dominant water-soluble nitrogen species in the atmosphere. Nitrate was the dominant inorganic nitrogen ion in precipitation.

These samples were used with 1000 hPa streamlines to classify sampled air masses according to their surface level transport and chemistry. Overall, mixed conditions occurred in 42% of the samples, continental species were dominant in 37%, and marine species were dominant in 21%. Rain occurred frequently under sea salt dominant conditions; about 47% of the days classified as such had rain events. Particulate NO3-- was associated with sea salt Na+ in the coarse aerosol fraction peaking at approximately 4 mum in diameter. Particulate NH4+ was associated with non-sea-salt-SO42--, with the bulk of the NH4+ present on particles in the 0.43--1.1 mum diameter range.

The direct atmospheric deposition of water-soluble nitrogen to the surface waters of the Gulf of Maine was assessed. Wet deposition dominated dry deposition, contributing 80--90% of the total flux annually. The total atmospheric direct nitrogen (ADN) deposition numbers reported here do not include the contributions of fog and dissolved organic nitrogen as they were not regularly sampled during this study. Total ADN flux ranged from 1--4262 mumol N m--2 d--1 (median 23 mumol N m --2 d--1), depositing 52 mmol N m --2 yr--1 to the surface waters of the Gulf of Maine, 3% of the total N input to those waters annually. However, this deposition was highly episodic with events over 500 mumol N m--2 d--1 occurring in 8% of the days sampled, but contributing 56% of the total measured flux. Estimates of the episodic atmospheric nitrogen flux to the Gulf of Maine surface waters suggest large deposition events could be sufficient to support substantial chlorophyll a production.

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