Uptake of Hydrogen Peroxide from the Gas Phase to Grain Boundaries: A Source in Snow and Ice.

Hydrogen peroxide is a primary atmospheric oxidant significant in terminating gas-phase chemistry and sulfate formation in the condensed phase. Laboratory experiments have shown an unexpected oxidation acceleration by hydrogen peroxide in grain boundaries. While grain boundaries are frequent in natural snow and ice and are known to host impurities, it remains unclear how and to which extent hydrogen peroxide enters this reservoir.

Hydrogen chloride (HCl) at ground sites during CalNex 2010 and insight into its thermodynamic properties.

Gas phase hydrogen chloride (HCl) was measured at Pasadena and San Joaquin Valley (SJV) ground sites in California during May and June 2010 as part of the CalNex study. Observed mixing ratios were on average 0.83 ppbv at Pasadena, ranging from below detection limit (0.

Kinetics of the oxidation of ammonia and amines with hydroxyl radicals in the aqueous phase.

While many studies have reported on the oxidation kinetics of ammonia and amines with the hydroxyl radical (OH) in the gas phase, the analogous reactions in the aqueous phase have not been adequately studied. In this work, the reaction rate constants of ammonia, dimethylamine (DMA) and diethylamine (DEA) with hydroxyl radicals in the aqueous phase were investigated using ion chromatography. The neutral and protonated forms of each base were shown to have differing rate constants with OH by performing the measurements over a range of pH from 7.

Simple Framework to Quantify the Contributions from Different Factors Influencing Aerosol pH Based on NH Phase-Partitioning Equilibrium.

While aerosol pH is among the most important parameters in atmospheric chemistry, it can be challenging to have a priori knowledge of the factors that are most strongly influencing the pH in a specific environment. In this study, we present a calculation method to more intuitively quantify the relationship between aerosol pH and its influencing factors, including gaseous NH concentration, particle properties, relative humidity, temperature, and nonvolatile cations, based on the NH phase-partitioning equilibrium used in the E-AIM thermodynamic model. The applications of this calculation framework include (1) expressing the pH values directly as the function of influencing factors, (2) quantitatively studying the contribution of different factors to pH value changes, and (3) decomposing the standard deviation of pH values to find the dominant influencing factors on total pH fluctuations.

Laboratory Investigation of Renoxification from the Photolysis of Inorganic Particulate Nitrate.

Nitrogen oxides (NO) play a key role in regulating the oxidizing capacity of the atmosphere through controlling the abundance of O, OH, and other important gas and particle species. Some recent studies have suggested that particulate nitrate, which is conventionally considered as the ultimate oxidation product of NO, can undergo "renoxification" via photolysis, recycling NO and HONO back to the gas phase. However, there are large discrepancies in estimates of the importance of this channel, with reported renoxification rate constants spanning three orders of magnitude.

Organic Peroxides and Sulfur Dioxide in Aerosol: Source of Particulate Sulfate.

Sulfur oxides (SO) are important atmospheric trace species in both gas and particulate phases, and sulfate is a major component of atmospheric aerosol. One potentially important source of particulate sulfate formation is the oxidation of dissolved SO by organic peroxides, which comprises a major fraction of secondary organic aerosol (SOA). In this study, we investigated the reaction kinetics and mechanisms between SO and condensed-phase peroxides.

Isocyanic acid (HNCO) and its fate in the atmosphere: a review.

Isocyanic acid (HNCO) has recently been identified in ambient air at potentially concerning concentrations for human health. Since its first atmospheric detection, significant progress has been made in understanding its sources and sinks. The chemistry of HNCO is governed by its partitioning between the gas and liquid phases, its weak acidity, its high solubility at pH above 5, and its electrophilic chemical behaviour.

Evidence for the Importance of Semivolatile Organic Ammonium Salts in Ambient Particulate Matter.

The gas/particle phase partitioning behavior of NH/NH and other semivolatile constituents was measured by a custom-designed Denuder-MOUDI-Denuder integrated sampling system in Toronto, Canada. In this setup, upstream denuders were used to capture alkaline and acidic gaseous components, and particle phase components were captured by the filters on MOUDI stages. Downstream denuders captured any alkaline and acidic gases that exited the MOUDI apparatus, likely representing semivolatile constituents.

Gas-Phase Mechanisms of the Reactions of Reduced Organic Nitrogen Compounds with OH Radicals.

Research on the fate of reduced organic nitrogen compounds in the atmosphere has gained momentum since the identification of their crucial role in particle nucleation and the scale up of carbon capture and storage technology which employs amine-based solvents. Reduced organic nitrogen compounds have strikingly different lifetimes against OH radicals, from hours for amines to days for amides to years for isocyanates, highlighting unique functional group reactivity. In this work, we use ab initio methods to investigate the gas-phase mechanisms governing the reactions of amines, amides, isocyanates and carbamates with OH radicals.

Nitrate Photolysis in Salty Snow.

Nitrate photolysis from snow can have a significant impact on the oxidative capacity of the local atmosphere, but the factors affecting the release of gas-phase products are not well understood. Here, we report a systematic study of the amounts of NO, NO, and total nitrogen oxides (NOy) emitted from illuminated snow samples as a function of both nitrate and total salt (NaCl and Instant Ocean) concentration. The results provide experimental evidence that the release of nitrogen oxides to the gas phase is directly related to the expected nitrate concentration in the brine at the surface of the snow crystals.

An Atmospheric Constraint on the NO2 Dependence of Daytime Near-Surface Nitrous Acid (HONO).

Recent observations suggest a large and unknown daytime source of nitrous acid (HONO) to the atmosphere. Multiple mechanisms have been proposed, many of which involve chemistry that reduces nitrogen dioxide (NO2) on some time scale. To examine the NO2 dependence of the daytime HONO source, we compare weekday and weekend measurements of NO2 and HONO in two U.

Atmospheric evolution of sulfur emissions from Kı̅lauea: real-time measurements of oxidation, dilution, and neutralization within a volcanic plume.

The high atmospheric concentrations of toxic gases, particulate matter, and acids in the areas immediately surrounding volcanoes can have negative impacts on human and ecological health. To better understand the atmospheric fate of volcanogenic emissions in the near field (in the first few hours after emission), we have carried out real-time measurements of key chemical components of the volcanic plume from Kı̅lauea on the Island of Hawai'i. Measurements were made at two locations, one ∼ 3 km north-northeast of the vent and the other 31 km to the southwest, with sampling at each site spanning a range of meteorological conditions and volcanic influence.

Experimental and theoretical understanding of the gas phase oxidation of atmospheric amides with OH radicals: kinetics, products, and mechanisms.

Atmospheric amides have primary and secondary sources and are present in ambient air at low pptv levels. To better assess the fate of amides in the atmosphere, the room temperature (298 ± 3 K) rate coefficients of five different amides with OH radicals were determined in a 1 m(3) smog chamber using online proton-transfer-reaction mass spectrometry (PTR-MS). Formamide, the simplest amide, has a rate coefficient of (4.

Gas phase oxidation of monoethanolamine (MEA) with OH radical and ozone: kinetics, products, and particles.

Monoethanolamine (MEA) is currently the benchmark solvent in carbon capture and storage (CCS), a technology aimed at reducing CO2 emissions in large combustion industries. To accurately assess the environmental impact of CCS, a sound understanding of the fate of MEA in the atmosphere is necessary. Relative and absolute rate kinetic experiments were conducted in a smog chamber using online proton transfer reaction mass spectrometry (PTR-MS) to follow the decay of MEA.

Insights into secondary organic aerosol formation mechanisms from measured gas/particle partitioning of specific organic tracer compounds.

In situ measurements of organic compounds in both gas and particle phases were made with a thermal desorption aerosol gas chromatography (TAG) instrument. The gas/particle partitioning of phthalic acid, pinonaldehyde, and 6,10,14-trimethyl-2-pentadecanone is discussed in detail to explore secondary organic aerosol (SOA) formation mechanisms. Measured fractions in the particle phase (f(part)) of 6,10,14-trimethyl-2-pentadecanone were similar to those expected from the absorptive gas/particle partitioning theory, suggesting that its partitioning is dominated by absorption processes.

Improved characterization of gas-particle partitioning for per- and polyfluoroalkyl substances in the atmosphere using annular diffusion denuder samplers.

Gas-phase perfluoroalkyl carboxylic acids (PFCAs) sorb strongly on filter material (i.e., GFF, QFF) used in conventional high volume air samplers, which results in an overestimation of the particle-phase concentration.

Characterization and optimization of an online system for the simultaneous measurement of atmospheric water-soluble constituents in the gas and particle phases.

In this work we present the results of extensive characterization and optimization of the Ambient Ion Monitor-Ion Chromatograph (AIM-IC) system, an instrument developed by URG Corp. and Dionex Inc. for simultaneous hourly measurements of the water-soluble chemical composition of atmospheric fine particulate matter (PM(2.