Role of Organic Coatings in Regulating N₂O₅ Reactive Uptake to Sea Spray Aerosol

Abstract

Previous laboratory measurements and field observations have suggested that the reactive uptake of N 2 O 5 to sea spray aerosol particles is a complex function of particle chemical composition and phase, where surface active organics can suppress the reactive uptake by up to a factor of 60. To date, there are no direct studies of the reactive uptake of N 2 O 5 to nascent sea spray aerosol that permit assessment of the role that organic molecules present in sea spray aerosol (SSA) may play in suppressing or enhancing N 2 O 5 uptake kinetics. In this study, SSA was generated from ambient seawater and artificial seawater matrices using a Marine Aerosol Reference Tank (MART), capable of producing nascent SSA representative of ambient conditions. The reactive uptake coefficient of N 2 O 5 (γ(N 2 O 5 )) on nascent SSA was determined using an entrained aerosol flow reactor coupled to a chemical ionization mass spectrometer for measurement of surface area dependent heterogeneous loss rates. Population averaged measurements of γ(N 2 O 5 ) for SSA generated from salt water sequentially doped with representative organic molecular mimics, or from ambient seawater, do not deviate statistically from that observed for sodium chloride (γ(N 2 O 5 ) NaCl = 0.01−0.03) for relative humidity (RH) ranging between 50 and 65%. The results are consistent with measurements made under clean marine conditions at the Scripps Institution of Oceanography Pier and those conducted on nascent SSA generated in the marine aerosol reference tank. The results presented here suggest that organic films present on nascent SSA (at RH greater than 50%) likely do not significantly limit N 2 O 5 reactive uptake.

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

“…29,30 Interestingly, studies seeking to replicate microbial blooms in a controlled manner (using informed representative organic species for each stage of the bloom) showed that N 2 O 5 uptake on SSA did not differ significantly from simplistic laboratory-generated NaCl particles (see Figure 3b). 31 This implies either (1) the complex nature of the organic species result in loose surface packing 20,32 or (2) the organic species are well mixed or present in low enough concentrations so as not to impact uptake. Both have significant implications for understanding how chemical changes dictate aerosol climate properties (i.e., heterogeneous reactivity, hygroscopicity, and interaction with solar radiation).…”

“…28 Segment B shows results that N 2 O 5 uptake is not suppressed in the presence of complex organics produced over the course of a microbial bloom. 31 Segment C illustrates a previously unrecognized reaction pathway for HNO 3 with functional groups present in bioorganic molecules produced during microbial blooms. 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.…”

Linking hygroscopicity and the surface microstructure of model inorganic salts, simple and complex carbohydrates, and authentic sea spray aerosol particles

“…organic component of the particle. 88 The calculated OVF as a function of particle size for the 1 : 1 mass ratios of NaCl/glucose and NaCl/laminarin is shown in Fig. 4C.…”

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.…”