4 research outputs found
HOx and NOx production in oxidation flow reactors via photolysis of isopropyl nitrite, isopropyl nitrite-d(7), and 1,3-propyl dinitrite at lambda=254, 350, and 369 nm
Oxidation flow reactors (OFRs) are an emerging technique for studying the formation and oxidative aging of organic aerosols and other applications. In these flow reactors, hydroxyl radicals (OH), hydroperoxyl radicals (HO2), and nitric oxide (NO) are typically produced in the following ways: photolysis of ozone (O-3) at), = 254 nm, photolysis of H2O at), = 185 nm, and via reactions of O(D-1) with H2O and nitrous oxide (N2O); O(D-1) is formed via photolysis of O-3 at = 254 nm and/or N2O at = 185 nm. Here, we adapt a complementary method that uses alkyl nitrite photolysis as a source of OH via its production of HO2 and NO followed by the reaction NO + HO2 -> NO2 + OH. We present experimental and model characterization of the OH exposure and NO, levels generated via photolysis of C3 alkyl nitrites (isopropyl nitrite, perdeuterated isopropyl nitrite, 1,3-propyl dinitrite) in the Potential Aerosol Mass (PAM) OFR as a function of photolysis wavelength (7, = 254 to 369 nm) and organic nitrite concentration (0.5 to 20 ppm). We also apply this technique in conjunction with chemical ionization mass spectrometer measurements of multifunctional oxidation products generated following the exposure of a-Pinene to HO, and NO, obtained using both isopropyl nitrite and O-3 + H2O + N2O as the radical precursors.Peer reviewe
Kinetics, Products, and Brown Carbon Formation by Aqueous-Phase Reactions of Glycolaldehyde with Atmospheric Amines and Ammonium Sulfate
Glycolaldehyde (GAld) is a C2 water-soluble aldehyde produced during the atmospheric oxidation of isoprene and many other species and is commonly found in cloudwater. Previous work has established that glycolaldehyde evaporates more readily from drying aerosol droplets containing ammonium sulfate (AS) than does glyoxal, methylglyoxal, or hydroxyacetone, which implies that it does not oligomerize as quickly as these other species. Here, we report NMR measurements of glycolaldehyde’s aqueous-phase reactions with AS, methylamine, and glycine. Reaction rate constants are smaller than those of respective glyoxal and methylglyoxal reactions in the pH range of 3–6. In follow-up cloud chamber experiments, deliquesced glycine and AS seed particles were found to take up glycolaldehyde and methylamine and form brown carbon. At very high relative humidity, these changes were more than 2 orders of magnitude faster than predicted by our bulk liquid NMR kinetics measurements, suggesting that reactions involving surface-active species at crowded air–water interfaces may play an important role. The high-resolution liquid chromatography–electrospray ionization–mass spectrometric analysis of filter extracts of unprocessed AS + GAld seed particles identified sugar-like C6 and C12 GAld oligomers, including proposed product 3-deoxyglucosone, with and without modification by reactions with ammonia to diimine and imidazole forms. Chamber exposure to methylamine gas, cloud processing, and simulated sunlight increased the incorporation of both ammonia and methylamine into oligomers. Many C4–C16 imidazole derivatives were detected in an extract of chamber-exposed aerosol along with a predominance of N-derivatized C6 and C12 glycolaldehyde oligomers, suggesting that GAld is capable of forming brown carbon SOA
Kinetics, products, and brown carbon formation by aqueous-phase reactions of glycolaldehyde with atmospheric amines and ammonium sulfate (Raw data)
The zipped data files are in the following formats: Metadata: Word documents (.docx), Chamber data: Excel spreadsheets (.xlsx) and European Data Format files (.edf), organized by experiment number and instrumentation. “CAPS” files contain cavity attenuated phase shift (CAPS) extinction and scattering data; “SMPS” files contain scanning mobility particle sizing aerosol number and aerosol mass data
Brown Carbon Production in Ammonium- or Amine-Containing Aerosol Particles by Reactive Uptake of Methylglyoxal and Photolytic Cloud Cycling
The
effects of methylglyoxal uptake on the physical and optical
properties of aerosol containing amines or ammonium sulfate were determined
before and after cloud processing in a temperature- and RH-controlled
chamber. The formation of brown carbon was observed upon methylglyoxal
addition, detected as an increase in water-soluble organic carbon
mass absorption coefficients below 370 nm and as a drop in single-scattering
albedo at 450 nm. The imaginary refractive index component <i>k</i><sub>450</sub> reached a maximum value of 0.03 ± 0.009
with aqueous glycine aerosol particles. Browning of solid particles
occurred at rates limited by chamber mixing (<1 min), and in liquid
particles occurred more gradually, but in all cases occurred much
more rapidly than in bulk aqueous studies. Further browning in AS
and methylammonium sulfate seeds was triggered by cloud events with
chamber lights on, suggesting photosensitized brown carbon formation.
Despite these changes in optical aerosol characteristics, increases
in dried aerosol mass were rarely observed (<1 ÎĽg/m<sup>3</sup> in all cases), consistent with previous experiments on methylglyoxal.
Under dry, particle-free conditions, methylglyoxal reacted (presumably
on chamber walls) with methylamine with a rate constant <i>k</i> = (9 ± 2) × 10<sup>–17</sup> cm<sup>3</sup> molecule<sup>–1</sup> s<sup>–1</sup> at 294 K and activation energy <i>E</i><sub>a</sub> = 64 ± 37 kJ/mol