Molecular Characterization of Nascent and Aged Sea Spray Aerosol

TL;DR

This study examines how sea spray aerosol particles change chemically when aged in a lab setup, revealing increases in organic compounds and sulfate.

Contribution

The study provides molecular-level insights into the chemical aging of sea spray aerosol and identifies specific organic species enhanced during aging.

Findings

Nascent SSA particles are primarily composed of inorganic ions, with organic carbon (OC) making up a small fraction.

Aging increases sulfate, phosphate, nitrate, ammonium, and OC concentrations relative to sodium, especially in submicron particles.

Organosulfates, including isoprene-derived ones, are significantly enhanced in aged SSA, indicating formation of secondary organic aerosol.

Abstract

The chemical aging of sea spray aerosol (SSA) was examined
in the
Sea Spray Chemistry and Particle Evolution (SeaSCAPE) experiment in
which nascent SSA particles were generated from seawater by breaking
waves in a glass wave channel. Particles and gases in the air in the
wave channel headspace were aged in an oxidative flow reactor. Nascent
SSA (before reaction) and aged SSA (after reaction) particles were
chemically analyzed for inorganic ions, organic carbon (OC), and select
organic species, including organosulfates, fatty acids, and alkyl
amines. Nascent SSA mass primarily consisted of inorganic ions associated
with sea salt. On average, OC accounted for 52% of particle mass <0.25
μm and 0.2% of mass in both supermicron and submicron particles,
with an increase in OC relative to Na+ with decreasing
particle size. The aging process increased the sulfate, phosphate,
nitrate, ammonium, and OC concentrations relative to sodium. The largest
increases in the sulfate and OC to Na+ ratios (by factors
of 7 and 5) in aged SSA were observed in particles with diameters
<0.25 μm. Organosulfates, which accounted for approximately
1% of SSA OC mass in PM1.0, were enhanced in aged SSA and
indicated the formation of low-volatility secondary organic aerosol
products associated with aging biological molecules such as unsaturated
fatty acids, isoprene, and monoterpenes. For example, isoprene-derived
organosulfates (e.g., 2-methyltetrol sulfate, C5H11SO7
–; m/z 215.0225) increased by a factor of 40 in samples of aged SSA and
marine volatile organic compounds. Among the strongest organosulfate
signals in nascent and aged SSA were alkyl organosulfates, which are
known to be anthropogenic surfactants in coastal waters. Homologous
series of saturated and unsaturated fatty acids, fatty acid derivatives,
and alkyl amines were also identified in nascent and aged SSA, with
some species enhanced by aging (i.e., diethylamine) and others not.
Together, these bulk and molecular analyses provide insight into molecular
modifications that occur upon the chemical aging of nascent SSA.

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