Estimation of rate coefficients and branching ratios for gas-phase reactions of OH with aliphatic organic compounds for use in automated mechanism construction

Reaction with the hydroxyl (OH) radical is the dominant removal process for volatile organic compounds (VOCs) in the atmosphere. Rate coefficients for reactions of OH with VOCs are therefore essential parameters for chemical mechanisms used in chemistry transport models, and are required more generally for impact assessments involving the estimation of atmospheric lifetimes or oxidation rates for VOCs. Updated and extended structure–activity relationship (SAR) methods are presented for the reactions of OH with aliphatic organic compounds, with the reactions of aromatic organic compounds considered in a companion paper. The methods are optimized using a preferred set of data including reactions of OH with 489 aliphatic hydrocarbons and oxygenated organic compounds. In each case, the rate coefficient is defined in terms of a summation of partial rate coefficients for H abstraction or OH addition at each relevant site in the given organic compound, so that the attack distribution is defined. The information can therefore guide the representation of the OH reactions in the next generation of explicit detailed chemical mechanisms. Rules governing the representation of the subsequent reactions of the product radicals under tropospheric conditions are also summarized, specifically their reactions with O2 and competing processes

Estimation of rate coefficients and branching ratios for reactions of organic peroxy radicals for use in automated mechanism construction

Organic peroxy radicals (RO2), formed from the degradation of hydrocarbons and other volatile organic compounds (VOCs), play a key role in tropospheric oxidation mechanisms. Several competing reactions may be available for a given RO2 radical, the relative rates of which depend on both the structure of RO2 and the ambient conditions. Published kinetics and branching ratio data are reviewed for the bimolecular reactions of RO2 with NO, NO2, NO3, OH and HO2; and for their self-reactions and cross-reactions with other RO2 radicals. This information is used to define generic rate coefficients and structure–activity relationship (SAR) methods that can be applied to the bimolecular reactions of a series of important classes of hydrocarbon and oxygenated RO2 radicals. Information for selected unimolecular isomerization reactions (i.e. H-atom shift and ring-closure reactions) is also summarized and discussed. The methods presented here are intended to guide the representation of RO2 radical chemistry in the next generation of explicit detailed chemical mechanisms

Estimation of rate coefficients for the reactions of O3 with unsaturated organic compounds for use in automated mechanism construction

Reaction with ozone (O3) is an important removal process for unsaturated volatile organic compounds (VOCs) in the atmosphere. Rate coefficients for reactions of 3with VOCs are therefore essential parameters for chemical mechanisms used in chemistry transport models. Updated and extended structure-activity relationship (SAR) methods are presented for the reactions of O3 with mono- and polyunsaturated organic compounds. The methods are optimized using a preferred set of data including reactions of O3 with 221 unsaturated compounds. For conjugated dialkene structures, site-specific rates are defined, and for isolated polyalkenes rates are defined for each double bond to determine the branching ratios for primary ozonide formation. The information can therefore guide the representation of the O3 reactions in the next generation of explicit detailed chemical mechanisms

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume VII-Criegee intermediates

This article, the seventh in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation. It covers an extension of the gas-phase and photochemical reactions related to Criegee intermediates previously published in Atmospheric Chemistry and Physics (ACP) in 2006 and implemented on the IUPAC website up to 2020. The article consists of an introduction, description of laboratory measurements, a discussion of rate coefficients for reactions of O3 with alkenes producing Criegee intermediates, rate coefficients of unimolecular and bimolecular reactions and photochemical data for reactions of Criegee intermediates, and an overview of the atmospheric chemistry of Criegee intermediates. Summary tables of the recommended kinetic and mechanistic parameters for the evaluated reactions are provided. Data sheets summarizing information upon which the recommendations are based are given in two files, provided as a Supplement to this article. © Author(s) 2020

Joint Polar Satellite System (JPSS) Micrometeoroid and Orbital Debris (MMOD) Assessment

The Joint Polar Satellite System (JPSS) Project requested the NASA Engineering and Safety Center (NESC) conduct an independent evaluation of the Micrometeoroid and Orbital Debris (MMOD) models used in the latest JPSS MMOD risk assessment. The principal focus of the assessment was to compare Orbital Debris Engineering Model version 3 (ORDEM 3.0) with the Meteoroid and Space Debris Terrestrial Environment Reference version 2009 (MASTER-2009) and Aerospace Debris Environment Projection Tool (ADEPT) and provide recommendations to the JPSS Project regarding MMOD protection. The outcome of the NESC assessment is contained in this report

Global modelling studies of hydrogen and its isotopomers using STOCHEM-CRI:Likely radiative forcing consequences of a future hydrogen economy

A global chemistry-transport model has been employed to describe the global sources and sinks of hydrogen (H2) and its isotopomer (HD). The model is able to satisfactorily describe the observed tropospheric distributions of H2 and HD and deliver budgets and turnovers which agree with literature studies. We than go on to quantify the methane and ozone responses to emission pulses of hydrogen and their likely radiative forcing consequences. These radiative forcing consequences have been expressed on a 1 Tg basis and integrated over a hundred-year time horizon. When compared to the consequences of a 1 Tg emission pulse of carbon dioxide, 1 Tg of hydrogen causes 5 ± 1 times as much time-integrated radiative forcing over a hundred-year time horizon. That is to say, hydrogen has a global warming potential (GWP) of 5 ± 1 over a hundred-year time horizon. The global warming consequences of a hydrogen-based low-carbon energy system therefore depend critically on the hydrogen leakage rate. If the leakage of hydrogen from all stages in the production, distribution, storage and utilisation of hydrogen is efficiently curtailed, then hydrogen-based energy systems appear to be an attractive proposition in providing a future replacement for fossil-fuel based energy systems

Investigating the background and local contribution of the oxidants in London and Bangkok

Birth registration marks a child’s right to identity and is the first step to establishing citizenship and access to services. At the population level, birth registration data can inform effective programming and planning. In Tanzania, almost two-thirds of births are in health facilities, yet only 26% of children under 5 years have their births registered. Our mixed-methods research explores the gap between hospital birth and birth registration in Dar es Salaam, Tanzania. Methods: The study was conducted in the two Tanzanian hospital sites of the Every Newborn-Birth Indicators Research Tracking in Hospitals (EN-BIRTH) multi-country study (July 2017–2018). We described the business processes for birth notification and registration and collected quantitative data from women’s exit surveys after giving birth (n = 8038). We conducted in-depth interviews (n = 21) to identify barriers and enablers to birth registration among four groups of participants: women who recently gave birth, women waiting for a birth certificate at Temeke Hospital, hospital employees, and stakeholders involved in the national birth registration process. We synthesized findings to identify opportunities to improve birth registration

A two-decade anthropogenic and biogenic isoprene emissions study in a London urban background and a London urban traffic site

A relationship between isoprene and 1,3-butadiene mixing ratios was established to separate the anthropogenic and biogenic fractions of the measured isoprene in London air in both urban background (Eltham) and urban traffic (Marylebone Road) areas over two decades (1997–2017). The average daytime biogenic isoprene mixing ratios over this period reached 0.09 ± 0.04 ppb (Marylebone Road) and 0.11 ± 0.06 ppb (Eltham) between the period of 6:00 to 20:00 local standard time, contributing 40 and 75% of the total daytime isoprene mixing ratios. The average summertime biogenic isoprene mixing ratios for 1997–2017 are found to be 0.13 ± 0.02 and 0.15 ± 0.04 ppb which contribute 50 and 90% of the total summertime isoprene mixing ratios for Marylebone Road and Eltham, respectively. Significant anthropogenic isoprene mixing ratios are found during night-time (0.11 ± 0.04 ppb) and winter months (0.14 ± 0.01 ppb) at Marylebone Road. During high-temperature and high-pollution events (high ozone) there is a suggestion that ozone itself may be directly responsible for some of the isoprene emission. By observing the positive correlation between biogenic isoprene levels with temperature, photosynthetically active radiation and ozone mixing ratios during heatwave periods, the Cobb-Douglas production function was used to obtain a better understanding of the abiotic factors that stimulate isoprene emission from plants. Other reasons for a correlation between ozone and isoprene are discussed. The long-term effects of urban stressors on vegetation were also observed, with biogenic isoprene mixing ratios on Marylebone Road dropping over a 20-year period regardless of the sustained biomass levels