https://ams.confex.com/ams/pdfpapers/71176.pdf

Fully coupled “online” chemistry within the WRF model

. Kinetic and mechanistic data relevant to the tropospheric degradation of volatile organic compounds (VOC), and the production of secondary pollutants, have previously been used to define a protocol which underpinned the construction of a near-explicit Master Chemical Mechanism. In this paper, an update to the previous protocol is presented, which has been used to define degradation schemes for 107 non-aromatic VOC as part of version 3 of the Master Chemical Mechanism (MCM v3). The treatment of 18 aromatic VOC is described in a companion paper. The protocol is divided into a series of subsections describing initiation reactions, the reactions of the radical intermediates and the further degradation of first and subsequent generation products. Emphasis is placed on updating the previous information, and outlining the methodology which is specifically applicable to VOC not considered previously (e.g. a - and b -pinene). The present protocol aims to take into consideration work available in the open literature up to the beginning of 2001, and some other studies known by the authors which were under review at the time. Application of MCM v3 in appropriate box models indicates that the representation of isoprene degradation provides a good description of the speciated distribution of oxygenated organic products observed in reported field studies where isoprene was the dominant emitted hydrocarbon, and that the a -pinene degradation chemistry provides a good description of the time dependence of key gas phase species in a -pinene/NOX photo-oxidation experiments carried out in the European Photoreactor (EUPHORE). Photochemical Ozone Creation Potentials (POCP) have been calculated for the 106 non-aromatic non-methane VOC in MCM v3 for idealised conditions appropriate to north-west Europe, using a photochemical trajectory model. The POCP values provide a measure of the relative ozone forming abilities of the VOC. Where applicable, the values are compared with those calculated with previous versions of the MCM.

/pdf/protocol-for-the-development-of-the-master-chemical-21efizove5.pdf

Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part A): tropospheric degradation of non-aromatic volatile organic compounds

Urban air pollution represents one of the greatest environmental challenges facing mankind in the 21st century. Noticeably, many developing countries, such as China and India, have experienced severe air pollution because of their fast-developing economy and urbanization. Globally, the urbanization trend is projected to continue: 70% of the world population will reside in urban centers by 2050, and there will exist 41 megacities (with more than 10 million inhabitants) by 2030. Air pollutants consist of a complex combination of gases and particulate matter (PM). In particular, fine PM (particles with the aerodynamic diameter smaller than 2.5 μm or PM_(2.5)) profoundly impacts
human health, visibility, the ecosystem, the weather, and the climate, and these PM effects are largely dependent on the aerosol properties, including the number concentration, size, and chemical composition. PM is emitted directly into the atmosphere (primary) or formed in the atmosphere through
gas-to-particle conversion (secondary) (Figure 1). Also,
primary and secondary PM undergoes chemical and physical
transformations and is subjected to transport, cloud processing, and removal from the atmosphere.

Formation of Urban Fine Particulate Matter

Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose (and some other sugars such as raffinose and polyols) across plant organs through the phloem. However, sugar transport through the phloem can be affected by many environmental factors that alter source/sink relationships. In this paper, we summarize current knowledge about the phloem transport mechanisms and review the effects of several abiotic (water and salt stress, mineral deficiency, CO2, light, temperature, air, and soil pollutants) and biotic (mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants) factors. Concerning abiotic constraints, alteration of the distribution of sugar among sinks is often reported, with some sinks as roots favored in case of mineral deficiency. Many of these constraints impair the transport function of the phloem but the exact mechanisms are far from being completely known. Phloem integrity can be disrupted (e.g., by callose deposition) and under certain conditions, phloem transport is affected, earlier than photosynthesis. Photosynthesis inhibition could result from the increase in sugar concentration due to phloem transport decrease. Biotic interactions (aphids, fungi, viruses…) also affect crop plant productivity. Recent breakthroughs have identified some of the sugar transporters involved in these interactions on the host and pathogen sides. The different data are discussed in relation to the phloem transport pathways. When possible, the link with current knowledge on the pathways at the molecular level will be highlighted.

/pdf/source-to-sink-transport-of-sugar-and-regulation-by-3izapdndox.pdf

Source-to-sink transport of sugar and regulation by environmental factors

The Secondary Organic Aerosol Model (SORGAM) has been developed for use in comprehensive air quality model systems. Coupled to a chemistry-transport model, SORGAM is capable of simulating secondary organic aerosol (SOA) formation including the production of low-volatility products and their subsequent gas/particle partitioning. The current model formulation assumes that all SOA compounds interact and form a quasi-ideal solution. This has significant impact on the gas/particle partitioning, since in this case the saturation concentrations of the SOA compounds depend on the composition of the SOA and the amount of absorbing material present. Box model simulations have been performed to investigate the sensitivity of the model against several parameters. Results clearly show the importance of the temperature dependence of saturation concentrations on the partitioning process. Furthermore, SORGAM has been coupled to the comprehensive European Air Pollution and Dispersion/Modal Aerosol Dynamics Model for Europe air quality model system, and results of a three-dimensional model application are presented. The model results indicate that assuming interacting SOA compounds, biogenic and anthropogenic contributions significantly influence each other and cannot be treated independently.

Modeling the formation of secondary organic aerosol within a comprehensive air quality model system

A new gas-phase chemical mechanism for the modeling of regional atmospheric chemistry, the “Regional Atmospheric Chemistry Mechanism” (RACM) is presented. The mechanism is intended to be valid for remote to polluted conditions and from the Earth's surface through the upper troposphere. The RACM mechanism is based upon the earlier Regional Acid Deposition Model, version 2 (RADM2) mechanism [Stockwell et al., 1990] and the more detailed Euro-RADM mechanism [Stockwell and Kley, 1994]. The RACM mechanism includes rate constants and product yields from the most recent laboratory measurements, and it has been tested against environmental chamber data. A new condensed reaction mechanism is included for biogenic compounds: isoprene, α-pinene, and d-limonene. The branching ratios for alkane decay were reevaluated, and in the revised mechanism the aldehyde to ketone ratios were significantly reduced. The relatively large amounts of nitrates resulting from the reactions of unbranched alkenes with NO3 are now included, and the production of HO from the ozonolysis of alkenes has a much greater yield. The aromatic chemistry has been revised through the use of new laboratory data. The yield of cresol production from aromatics was reduced, while the reactions of HO, NO3, and O3 with unsaturated dicarbonyl species and unsaturated peroxynitrate are now included in the RACM mechanism. The peroxyacetyl nitrate chemistry and the organic peroxy radical-peroxy radical reactions were revised, and organic peroxy radical +NO3 reactions were added.

/pdf/a-new-mechanism-for-regional-atmospheric-chemistry-modeling-1xgvkhtnkg.pdf

A new mechanism for regional atmospheric chemistry modeling

First-order sensitivity analysis of models with time-dependent parameters: an application to PAN and ozone

The kinetics of the reactions of selected secondary and tertiary peroxy radicals (RO2) with CH3C(O)O2 have been investigated. Values of (1.0±0.3)×10−11, (1.1±0.3)×−11(1.0±0.5)×10−11 and (1.1±0.3)×10−11 (units of cm3 molecule−1 s−1, statistical errors 2σ) have been obtained at 298 K for the rate constants of the reactions of CH3C(O)O2 radicals with c-C6H11O2, sec-C10H21O2, sec-C12H25O2 and t-C4H9O2 radicals, respectively. A systematic propagation of error analysis has yielded overall (statistical + systematical) uncertainty factors of 1.6, 1.8, 1.9, and 1.5, respectively, for the above rate constant values. The present results, combined with the results previously reported for primary peroxy radicals, show that all cross reactions of CH3C(O)O2 are fast with rate constants of around 1.0×10−11 cm3 molecule−1 s−1, independent of the RO2 radical structure and of its self-reaction rate constant. This suggests that all acylperoxy radicals present the same high reactivity as CH3C(O)O2, and hence it is proposed to assign the above rate constant value to all cross reactions of acylperoxy radicals. These new rate constant values were implemented in the Regional Atmospheric Chemistry Mechanism [Stockwell et al., 1997] to estimate the importance of the cross reactions in the chemistry of acylperoxy radicals in the troposphere. In the case of a moderately polluted troposphere, under low NOx and high volatile organic compounds (VOC) concentrations, the cross reactions of acylperoxy radicals with organic peroxy radicals account for more than 20% of the acylperoxy loss reactions, and peroxyacyl nitrates concentrations decrease by more than 4%, compared with the previous estimates of Kirchner and Stockwell [1996].

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JD00926

Kinetics and atmospheric implications of peroxy radical cross reactions involving the CH3C(O)O2 radical

A relative rate study has been performed on the reactions CH3C(O)O2• + NO2 + M → CH3C(O)O2NO2 + M (1) and CH3C(O)O2• + NO → CH3• + CO2 + NO2 (2) in an atmospheric flow system in which the relative yields of CH3C(O)O2NO2 (PAN) have been measured as a function of the ratio of reactants [NO]/[NO2]. Over the temperature range 247−298 K, at a total pressure of ∼1 atm, the ratio was independent of temperature, k1/k2 = 0.41 ± 0.03, where the error limits are 2σ. The results are discussed with reference to other relative rate measurements of k1/k2 and to absolute measurements of k1 and k2. The atmospheric implications of the ratio k1/k2 in relation to PAN are briefly considered.

Relative Rate Study of the Reactions of Acetylperoxy Radicals with NO and NO2: Peroxyacetyl Nitrate Formation under Laboratory Conditions Related to the Troposphere

Peroxyacyl nitrates [RC(O)OONO2] are formed in the atmosphere in the oxidative degradation of many organic compounds of both anthropogenic and biogenic origin. They are important oxidant components of photochemical smog and can cause eye irritation and plant damage. Moreover, peroxyacyl nitrates act as temporary reservoirs for reactive intermediates involved in photochemical smog formation, and they play an important role in the transport of NOx in the troposphere. It is therefore essential to establish reliable data on the kinetics and mechanisms of their formation and removal for inclusion in models of atmospheric chemistry. The kinetic data base for the most atmospherically abundant of the series, acetylperoxy nitrate [CH3C(O)OONO2, PAN], is quite well established, but data are lacking for the higher homologues, e.g., peroxypropionyl nitrate [CH3CH2C(O)O2NO2, PPN], which has also been detected in the troposphere. Here we report data on a relative rate study of the reactions CH3CH2C(O)O2· + NO2 + M → CH...

Kinetics of the Reactions of Propionylperoxy Radicals with NO and NO2: Peroxypropionyl Nitrate Formation under Laboratory Conditions Related to the Troposphere

Stephan Seefeld

Papers

A new mechanism for regional atmospheric chemistry modeling

First-order sensitivity analysis of models with time-dependent parameters: an application to PAN and ozone

Kinetics and atmospheric implications of peroxy radical cross reactions involving the CH3C(O)O2 radical

Relative Rate Study of the Reactions of Acetylperoxy Radicals with NO and NO2: Peroxyacetyl Nitrate Formation under Laboratory Conditions Related to the Troposphere

Kinetics of the Reactions of Propionylperoxy Radicals with NO and NO2: Peroxypropionyl Nitrate Formation under Laboratory Conditions Related to the Troposphere