This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

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The HITRAN 2008 molecular spectroscopic database

The optical properties of the light-absorbing, carbonaceous substance often called “soot,” “black carbon,” or “carbon black" have been the subject of some debate. These properties are necessary to model how aerosols affect climate, and our review is targeted specifically for that application. We recommend the term light-absorbing carbon to avoid conflict with operationally based definitions. Absorptive properties depend on molecular form, particularly the size of sp 2-bonded clusters. Freshly-generated particles should be represented as aggregates, and their absorption is like that of particles small relative to the wavelength. Previous compendia have yielded a wide range of values for both refractive indices and absorption cross section. The absorptive properties of light-absorbing carbon are not as variable as is commonly believed. Our tabulation suggests a mass-normalized absorption cross section of 7.5 ± 1.2 m2/g at 550 nm for uncoated particles. We recommend a narrow range of refractive indices for s...

https://www.tandfonline.com/doi/pdf/10.1080/02786820500421521

Light Absorption by Carbonaceous Particles: An Investigative Review

 Many atmospheric chemicals occur in the gas phase as well as in liquid cloud droplets and aerosol particles Therefore, it is necessary to understand the distribution between the phases According to Henry's law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution Henry's law constants of trace gases of potential importance in environmental chemistry have been collected and converted into a uniform format The compilation contains 17 350 values of Henry's law constants for 4632 species, collected from 689 references It is also available at http://wwwhenrys-laworg 

/pdf/compilation-of-henry-s-law-constants-version-4-0-for-water-58il9q0ogv.pdf

Compilation of Henry's law constants (version 4.0) for water as solvent

A review on the human health impact of airborne particulate matter

Atmospheric aerosols play important roles in climate and atmospheric chemistry: They scatter sunlight, provide condensation nuclei for cloud droplets, and participate in heterogeneous chemical reactions. Two important aerosol species, sulfate and organic particles, have large natural biogenic sources that depend in a highly complex fashion on environmental and ecological parameters and therefore are prone to influence by global change. Reactions in and on sea-salt aerosol particles may have a strong influence on oxidation processes in the marine boundary layer through the production of halogen radicals, and reactions on mineral aerosols may significantly affect the cycles of nitrogen, sulfur, and atmospheric oxidants.

https://science.sciencemag.org/content/sci/276/5315/1052.full.pdf

Atmospheric aerosols: Biogeochemical sources and role in atmospheric chemistry

Recent measurements of inorganic chlorine gases [1] and hydrocarbons [2] indicate the presence of reactive chlorine in the remote marine boundary layer; reactions involving chlorine and bromine can affect the concentrations of ozone, hydrocarbons and cloud condensation nuclei.

A mechanism for halogen release from sea-salt aerosol in the remote marine boundary layer

A detailed set of reactions treating the gas and aqueous phase chemistry of the most important iodine species in the marine boundary layer (MBL) has been added to a box model which describes Br and Cl chemistry in the MBL. While Br and Cl originate from seasalt, the I compounds are largely derived photochemically from several biogenic alkyl iodides, in particular CH2I2, CH2ClI, C2H5I, C3H7I, or CH3I which are released from the sea. Their photodissociation produces some inorganic iodine gases which can rapidly react in the gas and aqueous phase with other halogen compounds. Scavenging of the iodine species HI, HOI, INO2, and IONO2 by aerosol particles is not a permanent sink as assumed in previous modeling studies. Aqueous-phase chemical reactions can produce the compounds IBr, ICl, and I2, which will be released back into the gas phase due to their low solubility. Our study, although highly theoretical, suggests that almost all particulate iodine is in the chemical form of IO-3. Other aqueous-phase species are only temporary reservoirs and can be re-activated to yield gas phase iodine. Assuming release rates of the organic iodine compounds which yield atmospheric concentrations similar to some measurements, we calculate significant concentrations of reactive halogen gases. The addition of iodine chemistry to our reaction scheme has the effect of accelerating photochemical Br and Cl release from the seasalt. This causes an enhancement in ozone destruction rates in the MBL over that arising from the well established reactions O(1D) + H2O → 2OH, HO2 + O3 → OH + 2O2, and OH + O3 → HO2 + O2. The given reaction scheme accounts for the formation of particulate iodine which is preferably accumulated in the smaller sulfate aerosol particles.

Iodine chemistry and its role in halogen activation and ozone loss in the marine boundary layer: A model study

Aerosol pH in the marine boundary layer: A review and model evaluation

Mass spectrometric measurements of size and composition of diesel exhaust particles have been performed under various conditions: chassis dynamometer tests, field measurements near a German motorway, and individual car chasing. Nucleation particles consisting of volatile sulfate and organic material could be detected both at the chassis dynamometer test facility and during individual car chasing. We found evidence that if nucleation occurs, sulfuric acid/water is the nucleating agent. Low-volatile organics species condense only on the preexisting sulfuric acid/water clusters. Nucleation was found to depend strongly on various parameters such as exhaust dilution conditions, fuel sulfur content, and engine load. The latter determines the fraction of the fuel sulfur that is converted to sulfuric acid. The organic compounds (volatile and low-volatile) condense only on preexisting particles, such as both sulfuric acid nucleation particles and larger accumulation mode soot particles. On the latter, sulfuric acid also condenses, if the conditions for nucleation are not given. The overall ratio of sulfate to organic (volatile and low-volatile) is also strongly dependent on the engine load. It was found that the production of nucleation particles even at high engine load can be suppressed by using low-sulfur fuel.

Nucleation Particles in Diesel Exhaust: Composition Inferred from In Situ Mass Spectrometric Analysis

This paper explores the extent to which standard dilution tunnel measurements of motor vehicle exhaust particulate matter modify particle number and size. Steady state size distributions made directly at the tailpipe, using an ejector pump, are compared to dilution tunnel measurements for three configurations of transfer hose used to transport exhaust from the vehicle tailpipe to the dilution tunnel. For gasoline vehicles run at a steady 50 70 mph, ejector pump and dilution tunnel measurements give consistent results of particle size and number when using an uninsulated stainless steel transfer hose. Both methods show particles in the 10 100 nm range at tailpipe concentrations of the order of 104 particles/cm3. When an insulated hose, or one containing a silicone rubber coupler, is used to test small 4 cylinder gasoline vehicles, a very intense nanoparticle / ultrafine mode at < ~30 nm develops in the dilution tunnel particle size distribution as the vehicle speed is increased to 60 and 70 mph. This nanoparticle mode coincides with a rise of the transfer line temperature to about 180 250 °C. It is much less evident for the full size gasoline sedan, which has cooler exhaust. Both tailpipe and dilution tunnel measurements of diesel vehicle exhaust reveal an accumulation mode peak of ~108 particles/cm3, centered at 80 -100 nm. In this case, even with the uninsulated transfer hose an intense ultrafine peak appears in the dilution tunnel size distributions. This mode is attributed to desorption and/or pyrolysis of organic material, either hydrocarbon deposits on the walls of the steel transfer hose or the silicone rubber, by hot exhaust gases, and their subsequent nucleation in the dilution tunnel. This substantially limits the ability to make accurate particle number and size measurements using dilution tunnel systems. INTRODUCTION Prompted by potential health concerns, the past few years have witnessed a growing interest in particulate matter (PM) measurements, both ambient and from a wide variety of emissions sources. These measurements are conventionally performed by recording PM mass. The ambient standards are written in terms of mass concentrations, and emission regulations are based on mass rates. However, in order to understand better the nature of the mobile source contribution to ambient PM, many research groups are currently extending their investigations to include measurements of the numbers and sizes of particles in motor vehicle exhaust. Because the standard procedure for tailpipe PM measurements utilizes a dilution tunnel to cool the exhaust and to prevent water condensation, concerns have emerged that the test cell measurements of motor vehicle PM do not reflect the “real world” emissions. The root of the concern is that vehicle exhaust, a hot, complex, mixture of gaseous emissions and particles, is transformed differently when diluted in a tunnel as compared to the “real world”. Particles are not immutable; they readily undergo transformations, such as coagulation, condensation, and adsorption, and new particles can be created by nucleation of gaseous particle precursors in the diluted and cooled exhaust. Under “real world” conditions, motor vehicle exhaust is diluted rapidly, in less than one second, and by a large amount, a dilution ratio of greater than 100, into air of variable temperature and humidity. In the test cell, the exhaust is conducted to the dilution tunnel, typically by a 10 cm diameter by 5 m long tube, where it is then diluted by a factor of between 5 and 50, depending on test conditions, using dry air at room temperature. This discrepancy between dilution times, extents, temperature, and humidity can potentially lead to significant differences in the nature of the particulate emissions.

Rainer Vogt

Papers

A mechanism for halogen release from sea-salt aerosol in the remote marine boundary layer

Iodine chemistry and its role in halogen activation and ozone loss in the marine boundary layer: A model study

Aerosol pH in the marine boundary layer: A review and model evaluation

Nucleation Particles in Diesel Exhaust: Composition Inferred from In Situ Mass Spectrometric Analysis

Vehicle Exhaust Particle Size Distributions: A Comparison of Tailpipe and Dilution Tunnel Measurements