Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere.

The main nucleating vapor in the atmosphere is thought to be sulfuric acid (HSO), stabilized by ammonia (NH). However, in marine and polar regions, NH is generally low, and HSO is frequently found together with iodine oxoacids [HIO, i.e.

Synthesizing evidence for the external cycling of NO in high- to low-NO atmospheres.

External cycling regenerating nitrogen oxides (NO ≡ NO + NO) from their oxidative reservoir, NO, is proposed to reshape the temporal-spatial distribution of NO and consequently hydroxyl radical (OH), the most important oxidant in the atmosphere. Here we verify the in situ external cycling of NO in various environments with nitrous acid (HONO) as an intermediate based on synthesized field evidence collected onboard aircraft platform at daytime. External cycling helps to reconcile stubborn underestimation on observed ratios of HONO/NO and NO/NO by current chemical model schemes and rationalize atypical diurnal concentration profiles of HONO and NO lacking noontime valleys specially observed in low-NO atmospheres.

The gas-phase formation mechanism of iodic acid as an atmospheric aerosol source.

Iodine is a reactive trace element in atmospheric chemistry that destroys ozone and nucleates particles. Iodine emissions have tripled since 1950 and are projected to keep increasing with rising O surface concentrations. Although iodic acid (HIO) is widespread and forms particles more efficiently than sulfuric acid, its gas-phase formation mechanism remains unresolved.

Synergistic HNO-HSO-NH upper tropospheric particle formation.

New particle formation in the upper free troposphere is a major global source of cloud condensation nuclei (CCN). However, the precursor vapours that drive the process are not well understood. With experiments performed under upper tropospheric conditions in the CERN CLOUD chamber, we show that nitric acid, sulfuric acid and ammonia form particles synergistically, at rates that are orders of magnitude faster than those from any two of the three components.

Coupled Air Quality and Boundary-Layer Meteorology in Western U.S. Basins during Winter: Design and Rationale for a Comprehensive Study.

Wintertime episodes of high aerosol concentrations occur frequently in urban and agricultural basins and valleys worldwide. These episodes often arise following development of persistent cold-air pools (PCAPs) that limit mixing and modify chemistry. While field campaigns targeting either basin meteorology or wintertime pollution chemistry have been conducted, coupling between interconnected chemical and meteorological processes remains an insufficiently studied research area.

Direct field evidence of autocatalytic iodine release from atmospheric aerosol.

Reactive iodine plays a key role in determining the oxidation capacity, or cleansing capacity, of the atmosphere in addition to being implicated in the formation of new particles in the marine boundary layer. The postulation that heterogeneous cycling of reactive iodine on aerosols may significantly influence the lifetime of ozone in the troposphere not only remains poorly understood but also heretofore has never been observed or quantified in the field. Here, we report direct ambient observations of hypoiodous acid (HOI) and heterogeneous recycling of interhalogen product species (i.

Photo-oxidation of Aromatic Hydrocarbons Produces Low-Volatility Organic Compounds.

To better understand the role of aromatic hydrocarbons in new-particle formation, we measured the particle-phase abundance and volatility of oxidation products following the reaction of aromatic hydrocarbons with OH radicals. For this we used thermal desorption in an iodide-adduct Time-of-Flight Chemical-Ionization Mass Spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-ToF-CIMS). The particle-phase volatility measurements confirm that oxidation products of toluene and naphthalene can contribute to the initial growth of newly formed particles.

Molecular Composition and Volatility of Nucleated Particles from α-Pinene Oxidation between -50 °C and +25 °C.

We use a real-time temperature-programmed desorption chemical-ionization mass spectrometer (FIGAERO-CIMS) to measure particle-phase composition and volatility of nucleated particles, studying pure α-pinene oxidation over a wide temperature range (-50 °C to +25 °C) in the CLOUD chamber at CERN. Highly oxygenated organic molecules are much more abundant in particles formed at higher temperatures, shifting the compounds toward higher O/C and lower intrinsic (300 K) volatility. We find that pure biogenic nucleation and growth depends only weakly on temperature.

Multicomponent new particle formation from sulfuric acid, ammonia, and biogenic vapors.

A major fraction of atmospheric aerosol particles, which affect both air quality and climate, form from gaseous precursors in the atmosphere. Highly oxygenated organic molecules (HOMs), formed by oxidation of biogenic volatile organic compounds, are known to participate in particle formation and growth. However, it is not well understood how they interact with atmospheric pollutants, such as nitrogen oxides (NO ) and sulfur oxides (SO ) from fossil fuel combustion, as well as ammonia (NH) from livestock and fertilizers.

Rapid cycling of reactive nitrogen in the marine boundary layer.

Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed.

Formation of Low Volatility Organic Compounds and Secondary Organic Aerosol from Isoprene Hydroxyhydroperoxide Low-NO Oxidation.

Gas-phase low volatility organic compounds (LVOC), produced from oxidation of isoprene 4-hydroxy-3-hydroperoxide (4,3-ISOPOOH) under low-NO conditions, were observed during the FIXCIT chamber study. Decreases in LVOC directly correspond to appearance and growth in secondary organic aerosol (SOA) of consistent elemental composition, indicating that LVOC condense (at OA below 1 μg m(-3)). This represents the first simultaneous measurement of condensing low volatility species from isoprene oxidation in both the gas and particle phases.

Mercury Emission Ratios from Coal-Fired Power Plants in the Southeastern United States during NOMADSS.

We use measurements made onboard the National Science Foundation's C-130 research aircraft during the 2013 Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources, and Sinks (NOMADSS) experiment to examine total Hg (THg) emission ratios (EmRs) for six coal-fired power plants (CFPPs) in the southeastern U.S. We compare observed enhancement ratios (ERs) with EmRs calculated using Hg emissions data from two inventories: the National Emissions Inventory (NEI) and the Toxics Release Inventory (TRI).

ATMOSPHERIC SCIENCE. Comment on "Missing gas-phase source of HONO inferred from Zeppelin measurements in the troposphere".

Li et al. (Reports, 18 April 2014, p. 292) proposed a unity nitrous acid (HONO) yield for reaction between nitrogen dioxide and the hydroperoxyl-water complex and suggested a substantial overestimation in HONO photolysis contribution to hydroxyl radical budget.

Competing atmospheric reactions of CH2OO with SO2 and water vapour.

H2SO4 formation from the reaction CH2OO + SO2 has been measured as a function of the water vapour concentration for close to atmospheric conditions. Second-order kinetics with regard to water indicates a preferred reaction of CH2OO with the water dimer. The obtained kinetic parameters lead to the conclusion that the atmospheric fate of CH2OO is dominated by the reaction with water vapour.

Direct observations of atmospheric aerosol nucleation.

Atmospheric nucleation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the sub-2-nanometer (nm) size range, in which direct size-segregated observations have not been possible until very recently. Here, we present detailed observations of atmospheric nanoparticles and clusters down to 1-nm mobility diameter.

The role of sulfuric acid in atmospheric nucleation.

Nucleation is a fundamental step in atmospheric new-particle formation. However, laboratory experiments on nucleation have systematically failed to demonstrate sulfuric acid particle formation rates as high as those necessary to account for ambient atmospheric concentrations, and the role of sulfuric acid in atmospheric nucleation has remained a mystery. Here, we report measurements of new particles (with diameters of approximately 1.