Role of Organics in Regulating ClNO₂ Production at the Air–Sea Interface

Abstract

We report measurements of the product yield for nitryl chloride (ClNO2) production following the reactive uptake of dinitrogen pentoxide (N2O5) to a wide variety of ambient seawater samples as well as seawater mimics. The ClNO2 yield, as measured for ambient seawater collected from both coastal and open ocean waters, was found to be both insensitive to chlorophyll-a, a marker for biological activity, and significantly lower (0.16-0.30) than that expected for equivalent salt-containing solutions (0.82 ± 0.05). Suppression in the ClNO2 yield can be induced by the addition of aromatic organic compounds (e.g., phenol and humic acid) to synthetic seawater matrices. In the case of phenol, surface tension measurements reveal that the surface phenol:chloride ratio can be enhanced by more than a factor of 100 as compared to bulk ratios for subtle changes in surface tension (<1.5 mN m(-1)), providing a mechanism to suppress ClNO2 production at low bulk phenol concentrations. We interpret measurements of the dependence of the ClNO2 yield on phenol using a kinetic model, where we confine the surface enhancement in phenol to the top 1 nm of the interface. Our results are most consistent with a model where N2O5 is ionized within the first three water monolayers (<1 nm), where the product nitronium ions react rapidly with interfacial phenol molecules. These results suggest that ClNO2 may not be formed at the air-sea interface at the yield expected for NaCl, and that the reactive uptake of N2O5 and the subsequent product yield of ClNO2 may serve as a unique probe for the composition of the interfacial region of the sea surface microlayer.

Sea Spray Aerosol: The Chemical Link between the Oceans, Atmosphere, and Climate

“…This finding was attributed to the previously unrecognized atmospheric reaction path, where organic nitrification reactions between NO 2 + and aromatic rings in humic substances or proteins suppress the production of ClNO 2 (Figure 3d). 35 Previous studies in marine environments have shown a change in cloud properties in regions of phytoplankton blooms. It has been hypothesized that the critical factors that drive such changes are the relative organic content and composition of SSA particles as well as their size distributions and number concentrations.…”

“…34 Segment D shows a previously unrealized competition between aromatic organics and Cl − for NO 2 + resulting from N 2 O 5 uptake to a surface. 35 integrated methodologies. Thus, simple systems informed by results from complex systems have been utilized to establish model chemical systems that can be leveraged to provide parametrizations of SSA chemistry that improve the understanding of real world complexity in the future.…”

Estimating N&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; uptake coefficients using ambient measurements of NO&lt;sub&gt;3&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt;, ClNO&lt;sub&gt;2&lt;/sub&gt; and particle-phase nitrate

“…A value of k 4 /k 2 of 450 is presently recommended (Ammann et al, 2013), but may be modified for systems with a significant concentration of aromatics which can also react with hydrated nitronium ions (Ryder et al, 2015). Nitrate formed in the uptake of N 2 O 5 can partition to the gas phase as nitric acid or remain in the particle depending on the pH, available ammonia/ammonium and temperature.…”

Introductory lecture: atmospheric chemistry in the Anthropocene

“…[304][305][306] In the atmosphere, they can alter the exchange between the gas phase and clouds, fogs and particles, [307][308][309][310][311][312][313] change the kinetics of reactions such as the hydrolysis of NO 2 (ref. 173) and the oxidation of organics, 268,314,315 and alter ion composition and chemistry at the interface.…”

“…555,560 Organic coatings also appear to decrease N 2 O 5 uptake on particles, although this may be sensitive to the relative amounts of water present (and hence relative humidity) as well as the viscosity of the organic coating. 312,313,556,[561][562][563][564][565][566][567] If chloride ions are present, there is a competing reaction to form nitryl chloride, ClNO 2 . [568][569][570][571][572][573] It is interesting that the chloride ion reaction occurs at the interface, while that with water occurs deeper into the bulk of the particle.…”