Aircraft emissions play a role in human induced climate change, in particular condensation trails (contrails) formation, NOx and CO2 emissions. Recent years have seen increased research output in contrail studies and mitigation. Geo-engineering has gained attention in recent decades, with the objective to increase the global albedo resulting in reduced radiative forcing. Scenarios for geo-engineering include stratospheric aerosol injection (SAI), Marine Cloud Brightening (MCB), silver iodide injection as well as more niche scenarios. The interaction between aviation and geo-engineering remains underexplored. We explore the role of geo-engineering on contrail formation, persistence and aircraft plume chemistry employing the Aircraft Plume Chemistry, Emissions, and Microphysics Model (APCEMM). We apply this to jet fuel A-1 as well as potential alternative fuels with respective emission indices’ parameters including Synthetic aviation fuels (SAFs), hydrogen internal combustion jet engines and ammonia. We evaluate the chemistry background composition using theoretical adjustments and the G6-Sulfur experiment in CMIP6 model outputs. We explore how the result of increased particulate matter from increased aerosol number density, resulting from geo-engineering, facilitate the seeding of contrail formation. We find changes in ice crystal number density, heterogenous reaction rates of nitric acid, ozone perturbations optical depth of contrails, contrail lifetimes and total extinction, providing insights into the radiative forcings from SAI influenced contrails. [An increase in ice crystal number density is observed due to an abundance of sulfate aerosols acting as condensation nuclei. Reductions in the efficacy of alternative fuels such as hydrogen at minimising contrails, both in lifetime and forcing, when background aerosols replace soot as nucleating particles. Enhanced heterogonous reaction rate were found to increase HNO3 with SAI by 5 % for a 50 % increase in SO2 ]

Climate change will affect most of the world’s urban population. Developing resilient urban environments requires improved weather and climate modelling. Heterogeneity exists from street (100m) to neighbourhood (1km) to city (10km) scales due to urban form and function. How should it be parameterised, given that it influences atmospheric processes acting over a similar range of scales?To address this challenge, we combine city-scale field observations, resident interviews, high-resolution numerical (LES, NWP) and wind-tunnel (WT) modelling. The focus is on Bristol, UK, as it is compact, has representative land-use, and has coastal proximity and complex terrain. It follows other year-long urbisphere project campaigns in Berlin, Paris, Freiburg, and Heraklion.This talk provides an overview of the WT, LES and NWP modelling and observations thus far in the project. A case study is described where the sub-neighbourhood scale Avon River Gorge influences boundary layer and dispersion processes.

Climate change already affects most of the world’s urban population. Developing resilient urban environments requires improving both weather and climate modelling. Heterogeneity exists from street (100 m) to neighbourhood (1 km) to city (10 km) scales due to urban form and function. Hectometric-scale numerical weather prediction (NWP) may be starting to resolve neighbourhood-scale heterogeneity but how can observation networks be designed to capture spatial variation in urban climates (horizontally and vertically) to evaluate these model predictions robustly?To address these challenges, we combine city-scale field observations, resident interviews, high-resolution numerical (Large Eddy Simulation, NWP) and wind-tunnel modelling. Three research projects (ASSURE, urbisphere, and UrbanAIR) have collaborated to design and maintain an urban observation network in the UK. The focus is on Bristol as it is compact, has representative land-use, is close to the coast, and lies in relatively low-lying complex terrain. Bristol City authorities had previously used Met Office climate simulations at 2.2 km resolution to plan for urban heat vulnerability. Both partners were engaged in our design of a network of over 40 lamp-post mounted automatic weather stations that has run since spring 2024. A network of ground-based remote sensing (Doppler wind lidars, automatic lidar ceilometers) was deployed at six sites across the city to observe boundary layer development in response to the urban surface and orography. Other observations included indoor climate, radiation, vegetation, and tracer gas dispersion experiments. The core Bristol field campaign ran from spring 2024-2025 but a sub-set of measurements is ongoing. This follows other year-long urbisphere campaigns in Berlin, Paris, Freiburg, and Heraklion.This talk provides an overview of the observation network in the Bristol project and the data-set obtained. Key findings will be presented where field and modelling approaches were combined to design the deployment, e.g., a Virtual Doppler Lidar approach using LES, lessons learned from a testbed of a high-resolution NWP ensemble.

Quintero is a Chilean coastal city located 40 km north of Valparaiso. In the surroundings of Quintero, there are a number of industries that generate high levels of atmospheric pollutants such as sulfur dioxide (SO2), nitrogen oxides (NOx), carbon monoxide (CO) and non-methane hydrocarbons (NMHCs). These compounds may also be generated during oil handling in storage facilities in this area. Quintero Bay has a port that is being used mainly for oil and copper transportation. Since 2010, there have been reports of events producing nausea, vomiting and abdominal pain in the residents of Quintero, and some previous studies have correlated these medical events with high concentrations of SO2 and NMHCs. One of the main sources of SO2 in the area was identified to be the Ventanas copper foundry. Following public pressure, the government stopped the operation of the foundry by mid-2023, which led to a significant decrease in SO2 levels. However, reports of health problems persisted to some extent. In this work, delayed cross-correlation, trajectory and dispersion analyses indicate that an upwind source of air pollution impacting Quintero originates near the oil refinery in Concón, located 20 km to the south. This source of air pollution could provide a background of NMHCs, over which local emissions add up to attain very high concentrations in Quintero. Our analysis shows that there is evidence of the transport of NMHCs from the Concón refinery to the Quintero area. In 2022, of the 20 days with NMHC concentrations greater than 200 ppvb, 50% of them were associated with prevalent southwest winds. Using trajectory and dispersion analyses for eight episodes in Quintero, it has been found that an approximate fraction of pollution generated in Concón that could arrive in Quintero is between 2 and 24%.

Abstract. A large discrepancy of at least 10 Gg yr-1 exists between reported emissions of the potent greenhouse gas HFC-23 (CHF3, trifluoromethane) and emissions derived from atmospheric measurements. In-atmosphere production of HFC-23 from the breakdown of fluorinated source gases such as hydrofluorocarbons and hydrofluoroolefins contributes to this gap, but the magnitude of this source is weakly constrained. This uncertainty is due, in part, to limited experimental measurements of the photolysis quantum yield of trifluoroacetaldehyde (CF3CHO), a key degradation product which forms HFC-23 via photolysis. The parameters governing CF3CHO deposition are also poorly understood. Previous work reported an upper limit of the contribution of the in-atmosphere source to the global HFC-23 burden. Here, we use a 3D chemistry and transport model to further constrain this contribution, using recent estimates of source gas emissions, kinetic rate constants, photolysis rates and deposition parameters, as well as considering the uncertainties in these values. We find that in-atmosphere production of HFC-23 is in the range 0.013–0.035 Gg yr−1, significantly lower than previous estimates. This accounts for <0.5 % of the discrepancy between reported emissions and those derived from atmospheric observations, suggesting that this source makes a negligible contribution to the overall HFC-23 budget. As part of this work, we also calculate indirect global warming potentials for the HFC-23 source gases HFO-1234ze(E), HFO-1336mzz(Z) and HCFO-1233zd(E) and find that their impact on climate is up to ten times higher than previously reported.

Aviation is widely recognised to have global-scale climate impacts through the formation of ozone (O3) in the upper troposphere and lower stratosphere (UTLS), driven by emissions of nitrogen oxides (NOX). Ozone is known to be one of the most potent greenhouse gases formed from the interaction of aircraft emission plumes with atmospheric species. This paper follows up on previous research, where a Photochemical Trajectory Model was shown to be a robust measure of ozone formation along flight trajectories post-flight. We use a combination of a global Lagrangian chemistry-transport model and a box model to quantify the impacts of aircraft NOX on UTLS ozone over a five-day timescale. This work expands on the spatial and temporal range, as well as the chemical accuracy reported previously, with a greater range of NOX chemistry relevant chemical species. Based on these models, route optimisation has been investigated, through the use of network theory and algorithms. This is to show the potential inclusion of an understanding of climate-sensitive regions of the atmosphere on route planning can have on aviation’s impact on Earth’s Thermal Radiation balance with existing resources and technology. Optimised flight trajectories indicated reductions in O3 formation per unit NOX are in the range 1–40% depending on the spatial aspect of the flight. Temporally, local winter times and equatorial regions are generally found to have the most significant O3 formation per unit NOX; moreover, hotspots were found over the Pacific and Indian Ocean.

Urban air flow is affected by topography, built environment and meteorology in a way that can be difficult to predict. The deliberate release of inert, non-toxic tracers can provide measurements of air flow. A series of experiments in Bristol, UK, have used inert perfluorocarbon tracers to investigate the dispersion effects. Tracer data can be used to validate wind tunnel models and large eddy simulations of the test area.The River Avon, flows from the Severn Estuary through a gorge to the west of the city of Bristol into the Harbour. Hills of up to100 m elevation surround this location and tracer campaigns have been conducted in the Cotham area uphill and to the north. Modelling has shown the gorge to be important for the circulation of winds in the city, and a vehicle fire in the South East in January 2021 provided an example of pollutants being recirculated through the city.Tracers were released for 15 minutes and air sampled for 30 minutes in Tedlar bags in multiple locations for offline analysis by GCMS. Three releases from the North West in June 2021 with wind speeds between 1 and 4 m s-1 were detected 1.5 km downwind from the release point, but measurements from a similar distance from the South, North and South West in January 2022 at ~1 m s-1 were more disperse. Tracer releases with a southerly wind of up to 2 m s-1 in the Cotham area in September 2024 have shown that over the short distance scale, tracers follow street networks in the predominant wind direction. Perfluoromethylclohexane released on a street at the bottom of a hill was measured at 1741 ppq 320 m up the hill, but less than 550 ppq on side streets 400 m up the hill in the predominant wind direction.

The potential transition to a hydrogen-based economy, requires a comprehensive understanding of hydrogen's atmospheric behaviour for well-informed decision-making. Among the uncertainties surrounding the atmospheric fate of hydrogen, the chemical processes governing its formation and transformation are pressing. This study employs STOCHEM-CRI, a global 3D tropospheric chemical transport model, to explore the chemical uncertainty associated with atmospheric hydrogen. The primary objective is to improve our understanding of the hydrogen distribution, sources, and sinks on a global scale. Addressing the significant role of formaldehyde (HCHO) as a chemical source, we update its photolysis parameterisation in accordance with recent recommendations (JPL 2020 and IUPAC 2013) and assess its variability. Furthermore, we evaluate the atmospheric burden of HCHO as a function of its sources to identify key photochemical contributors to the present hydrogen budget. The study undertakes preliminary studies of the major sink of atmospheric hydrogen, namely uptake by soil, to gauge its impact. Through a meticulous examination of model outputs against observational data, various scenarios are systematically assessed for their ability to accurately replicate global hydrogen distribution and seasonal variations. Preliminary results show updates to the photochemical parameters of HCHO significantly reduce the hydrogen burden by between 50 and 90 ppb globally. This is namely due to updates to the quantum yield of the molecular (H2 producing) photolysis channel which varies significantly when compared to previous recommendations. There is limited variation between the two updates (JPL 2020 and IUPAC 2013) of up to 5 ppb. Additionally, minor updates relating to the temperature dependence of the soil sink result in significant improvement in the models replication of observational data, including seasonal variation.

Isoprene emissions can affect the oxidizing capacity of the atmosphere and are likely to increase with an increase in the world’s biomass. The emission of isoprene is strongest in tropical forested regions, suggesting a major portion of tropospheric chemistry occurs in the tropics. As well as deforestation and reforestation having a direct impact on the world’s climate through land cover, there is also an indirect environmental impact (e.g., global warming, air pollution) through the resulting change in isoprene emissions. Previously, incomplete understanding of isoprene oxidation chemistry caused a model-measurement breakdown for concentrations of HOx radicals observed over certain low-NOx regions, such as the pristine Amazon rainforest. Over the last decade, however, understanding of isoprene oxidation chemistry has been vastly improved. Numerous research studies have provided evidence for the involvement of 1,6-H and 1,5-H shift reactions in the isoprene oxidation mechanism, which increases the level of HOx recycling that occurs. As well as helping to reduce the model-measurement breakdown observed, the updated isoprene oxidation mechanism affects the tropospheric burdens of other species, including carbon monoxide (CO), methane (CH4), ozone (O3), organic peroxides (ROOH), secondary organic aerosol (SOA), and organic nitrates (RONO2). There are still gaps in the understanding of the impacts and oxidation chemistry of isoprene emissions, which this literature review identifies and discusses. In the future, there is still much scope for further research, including modeling future reforestation scenarios with isoprene emissions and their impacts on both global and regional scales.

The pandemic was a very difficult time for everyone, as well as teachers and their students. Teachers of first-year quantitative chemistry courses, both during the pandemic and postpandemic, encountered many pandemic-induced difficulties, including inter alia communicating with individual students, providing them with rapid formative feedback, and determining where they were on their learning journey. In addition, two cohorts of students requiring different teaching approaches were enrolled on this course during the period of this study (2020-2023). One cohort had a post-16 mathematics qualification (A-level that includes calculus) and the other, a pre-16 mathematics qualification (GCSE that does not include calculus) as their highest mathematics qualification. In this Article, we show the value of using Smart Worksheets to address these challenges. The Smart Worksheets provided valuable information about the students' ability to apply mathematical concepts within a chemistry context and, consequently, allowed the teaching team to shape workshops to cater for any application difficulties. Smart Worksheets clearly identified a number of (basic) skills that many of the students were struggling with, including graphing, uncertainty analysis, application of units, and application of logs to buffer calculations. Smart Worksheets also allowed the teaching team to connect with students, to either commend them on their work or ask how they were coping if they appeared to be struggling. Students highlighted how the instant formative feedback provided by Smart Worksheets and their unlimited availability during the course impacted positively on their learning. The Smart Worksheets also helped to identify two subgroups in the student cohort with the higher mathematics qualification; one subgroup could apply their mathematics knowledge within different chemistry contexts while the other subgroup was not able to move from a mathematical context to a chemistry context. This information allowed the teaching team to alter workshop approaches to emphasize translation from one context to another.

A Pollutant's Tale and its primary school version, Gases in the Air, are two talks that have been developed and modified over the last ca. 18 years, that provide audiences from approximately 4-90 years old with the background to the composition of the Earth's lower atmosphere, the Earth's climate, and the impact of air pollution. In this article, we describe the content of the talks and provide videos of each experiment individually as well as a recorded performance of both talks to an empty auditorium. In this article, we discuss ways that the talk can be further developed and its impact on audiences.

The transition to university-level chemistry often reveals numeracy skills gaps that can hinder student confidence and academic success. Online learning tools can help characterise and address these gaps. This study introduces a Scientific Numeracy Smart Worksheet (SNSW) resource to characterise and address the numeracy-based strengths and weaknesses of a large cohort of first-year chemistry students at a South African university. We also investigated student usage and perceptions of this educational resource. The SNSW integrates core mathematical concepts with subject-specific contexts, features high levels of feedback, value randomisation, and an auto-solve feature for struggling students. It was offered as formative support for chemistry students near the start of their university journey. Usage and performance analytics from consenting students were used to study overall and section-level SNSW performance, while an anonymous questionnaire explored student perceptions. Students performed well at ‘Displaying numbers’ (85%) and ‘Rearranging and solving equations’ (84%). The lowest scoring sections were ‘Graphs’ (64%) and ‘Averages and spread of data’ (72%). ‘Scientific units’ showed the highest auto-solve percentage. Students who repeated the SNSW scored significantly higher and used the auto-solve feature significantly less on the second attempt (both p < 0.001) and scored higher in quantitative components of their end-of-module assessment, but not significantly so (p = 0.082). The questionnaire indicated high student rating for the SNSW (8.2/10), with most students finding it helpful and at the appropriate level. Providing supportive and diagnostic resources can help students develop numeracy skills and identify areas for personal improvement. Instantaneous data, generated from each student engagement with SNSW, can assist staff to develop educational strategies to target specific transitional skill deficiencies. Significance: Learners at secondary schools and university students alike struggle with basic numeracy concepts, such as ratios and proportions, graphs and SI units. First year chemistry curricula are full, with little time spent on revising content from school. The SNSW is a means of solving this problem. Students work through the worksheets at their own pace and receive immediate feedback. This research highlights both the gaps in students’ numeracy skills, and a corrective intervention by first-year chemistry lecturers.

In this study, a global Lagrangian chemistry-transport model, STOCHEM-CRI, was employed to study the formation of hydrogen (H-2) from the oxidation of twenty anthropogenic and natural biogenic non-methane volatile organic compounds (VOCs). The base case STOCHEM-CRI model was perturbed by applying a step-change to the emissions of each VOC in turn. Differences between each perturbed case and the base case were used to derive the responses in the fluxes through the formaldehyde photolysis source of H-2 and in the oxidation rate of each VOC. H-2 yields were largest for the natural biogenic VOCs: isoprene, alpha- and beta-pinene and least, close to zero, for ethyne and benzene. Differences in yields were driven by the number of carbon atoms, by the chemical mechanisms of the hydroxyl radical and ozone reactions and by the involvement of long-lived oxidation products. These responses were then used to estimate the global H-2 source strengths from the oxidation of anthropogenic and natural biogenic VOCs. Ethene oxidation dominated the global H-2 source from the oxidation of anthropogenic VOCs, totalling 1.6 Tg yr(-1). Isoprene oxidation dominated the natural biogenic VOC oxidation source, totalling 20 Tg yr(-1), over ten times higher than the anthropogenic source. Uncertainties in the VOC oxidation source of H-2 make a considerable contribution to the uncertainties in the global warming potentials for H-2 estimated with current chemistry-transport models.

Particulate matter in the atmosphere is a major health concern, and the chemical composition of particles will affect its toxicology. Chemical composition of PM10 can indicate likely sources of pollutants; high concentrations of metals can come from fuel mixtures, lubricants, abrasion and engine wear from cars [1], while polycyclic aromatic hydrocarbons (PAH) are produced by combustion sources [2]. Measurements can be interpreted through use of air flow measurements within the city and supported modelling [3].PM10 samples were collected weekly, every Thursday, for 24 hours from a 1st floor balcony at the We the Curious science museum in central Bristol, UK. Samples were collected using a Sven Leckel LVS3 PM10 sampler on a 47 mm quartz filter and weighed to calculate the mass concentration. Quartz filters were halved and analysed for metals using ICP-MS and for PAH using GC-MS. Local meteorology was measured on the roof using a Gill Maximet 501 weather station.Measurements took place from February 2021 until February 2022. Within the UK the third COVID-19 lockdown started on 6th January 2021 and was incrementally lifted from 8th March until 21st June when all restrictions were removed.Taking the average of samples that were detected above noise average metal concentrations from lowest (Co, 40 ng/m3) to highest (Fe 195 µg/m3) were Co < Li < Ce < Cd < La < Rb < Bi < Se < V < Sb < As < Sr < Sn < Pb < Mn < Ba< Cu < Zn < Al < Mg< Fe. Average PAH concentrations from lowest to highest were Anthracene < Fluoranthene < Pyrene < Acenaphthene < Dibenzo-a,h-Anthracene < Benzo[k]Fluoranthene < Indeno-123-cd-Pyrene < Chrysene < Benzo[a]Pyrene < Benzo-ghi-Perylene < Benzo[a]Anthracene < Benzo[b]Fluoranthene, average total PAH concentration was 4.8 ng/m3).For the sample collected from 13th January 2022, many metals and PAH levels were elevated. This coincided with a multivehicle fire in Totterdown, around 2 km South East of the measurement position, that started in the evening of the 13th. Total PAH, Mn, Co, Cu, As, Rb, Cd, Sn, Sb, Ba, Ce, Pb and Bi were more than 2 standard deviations higher than the weekly mean concentrations, many showing a 2-3 fold increase. Measurements of Nitric Oxide from the UK government AURN air quality site in St Pauls, ~2 km from the We the Curious site ~3 km north of the incident site, confirmed that pollutants were dispersed city wide, not local to the measurement position. The predominant wind direction was south westerly on the 13th January, but air masses can spread through a complex city terrain against wind directions [3].Measurements in a single location can provide information on pollution in the city, extreme peaks in concentrations were identified with fires being a likely source.[1] Pulles T, van der Gon HD, Appelman W, Verheul M 2012. Atmos Environ 61, 641–651.[2] Jang, E., Alam, M.S. and Harrison, R.M., 2013. Atmospheric Environment, 79, 271-285.[3] Matthews, J.C., Wright, M.D., Martin, et al. 2020. Boundary-Layer Meteorology, 175, 113-134.

HFC-23 (trifluoromethane) is a potent greenhouse gas, believed to be emitted to the atmosphere primarily as a by-product during the production of the refrigerant and feedstock HCFC-22 (chlorodifluoromethane). Due to the high global warming potential of HFC-23 (GWP100 ~ 14,700), the Kigali Amendment to the Montreal Protocol requires countries to limit their emissions of HFC-23 as much as possible and report these emissions to the United Nations Environment Programme. Global reported emissions have been in the range 2-3 Gg yr-1 since 2019 and reflect the near-total destruction of emissions from HCFC-22 production reported by the countries with major HCFC-22 manufacturers, such as China and India. However, atmospheric observations show that, whilst emissions fell from their maximum in 2019 of 17.3 ± 0.8 Gg yr-1 to 14.0 ± 0.9 Gg yr-1 in 2023, they remain many times higher than reported. In addition, regional inverse modelling was performed based on measurements from the AGAGE site at Gosan, South Korea, using three different Bayesian inverse models (FLEXINVERT+, InTEM and RHIME) to estimate emissions from eastern China. These inversions use the same observational data, but different transport models, baselines, priors and uncertainties. Results are compared to better quantify regional emissions and their uncertainties. The results suggest that emissions from eastern China are four to six times higher than reported for the whole of China. In addition, we examine the emission of HFC-23 as a by-product during the production of other hydrofluorocarbons and fluorochemicals. In-atmosphere HFC-23 production (from the breakdown of certain hydrofluoroolefins used as replacements for HFCs) is also investigated further using a 3D chemical transport model incorporating photolysis and ozonolysis reactions. Our results indicate that, based on currently available information, these potential alternative sources contribute less than 2.0 Gg yr-1 to global emissions. This suggests that HFC-23 emissions from HCFC-22 production have been consistently under-reported since the implementation of the Kigali Amendment. It therefore appears likely that abatement of HFC-23 emissions has not occurred to the extent reported in this period. Improved monitoring and verification of HFC-23 emissions from industrial sources is essential to the continued success and efficacy of the Kigali Amendment.

OH+NO is an important termolecular association reaction in the troposphere and stratosphere that influences the atmospheric ozone budget. In this study, rate coefficients for the reaction of OH + NO + M → HONO + M were measured under conditions relevant to the troposphere/lower stratosphere over a temperature range of 228-298 K and pressure range of 50-750 Torr using N2 as a bath gas. Time-resolved kinetics were studied by pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) detecting OH by laser-induced fluorescence. Data for the temperature range 258-298 K were fit to two falloff expressions, with the JPL expressions (k1,0N2 = 7.37 × 10-31(T/300 K)-2.90 cm6 molecule-2 s-1 and k1,∞ = 3.44 × 10-11(T/300 K)-0.1cm3 molecule-1 s-1) and IUPAC expression (k1,0N2 = 6.80 × 10-31(T/300 K)-2.81 cm6 molecule-2 s-1, FC = 0.81, k1,∞ = 1.96 × 10-11(T/300 K)-0.3 cm3 molecule-1 s-1). At temperatures T < 258 K, the measured rate coefficients were significantly higher than the IUPAC and JPL fits. To accommodate the rate coefficient deviation from the two expressions, data across the entire temperature range (228-298 K) was fit with two approaches. First, rate coefficients were fit with an empirical modification by adding a second falloff term to the JPL expression with a second low-pressure rate coefficient of k1,0N2 = 5.20 × 10-35(T/300 K)-30.4 cm6 molecule-2 s-1. Second, k1,0N2, k1,∞, and n were fit globally to the entire temperature data set, but FC was varied for each individual temperature, which increased with decreasing temperature. In the second portion of the study, the influence of H2O on the reaction rate was investigated using a N2-H2O mixture as the bath gas at 50 Torr and 273 and 298 K. The JPL and IUPAC falloff expressions were modified to include H2O as a third-body collisional partner consistent with a nonlinear mixture model. Fits to the data yielded the low pressure termolecular rate coefficients in H2O, k1,0H2O = 3.81 × 10-30(T/300 K)-6.04 and k1,0H2O = 3.31 × 10-30(T/300 K)-5.81 cm6 molecule-2 s-1, respectively. Experimental data were fit using MESMER give energy relaxation parameters of <ΔEdown,295 K, N2> = 170 ± 10 cm-1 and <ΔEdown,295 K,H2O> = 634 ± 20 cm-1, indicating that H2O is a 4× more efficient collisional quencher than N2 alone. The modified JPL expressions with the newly derived low pressure rate coefficients were implemented into a STOCHEM-CRI atmospheric model. Predictions of HONO concentrations with the new rates were up to 15% higher in remote tropical regions.

Incorporating the reactions of fifty peroxy radicals (RO2) with the hydroxyl radical (OH) into the global chemistry transport model, STOCHEM-CRI, affected the composition of the troposphere by changing the global burdens of NOx (-2.7 Gg, -0.5%), O3 (-2.3 Tg, -0.7%), CO (-3.2 Tg, -0.8%), HOx (+2.1 Gg, +7.7%), H2O2 (+0.5 Tg, +18.3%), RO2 (-8.0 Gg, -18.2%), RONO2 (-19.4 Gg, -4.7%), PAN (-0.1 Tg, -3.4%) HNO3 (-7.4 Gg, -1.3%) and ROOH (-96.9 Gg, -3.8%). The RO2 + OH addition reactions have a significant impact on HO2 mixing ratios in tropical regions with up to a 25% increase, resulting in increasing H2O2 mixing ratios by up to 50% over oceans. Globally, a significant amount of organic hydrotrioxides (ROOOH) (86.1 Tg per year) are produced from these reactions with CH3OOOH (67.5 Tg per year, 78%), isoprene-derived ROOOH (5.5 Tg per year, 6%) and monoterpene-derived ROOOH (4.2 Tg per year, 5%) being the most significant contributors. The tropospheric global burden of CH3OOOH is found to be 0.48 Gg. The highest mixing ratios of ROOOH, of up to 0.35 ppt, are found primarily in the oceans near the tropical land areas. The RO2 + OH reactions have a small, but noticeable, contribution to OH reactivity (similar to 5%) over tropical oceans. Additionally, these reactions have a significant impact on RO2 reactivity over tropical oceans where losses of the CH3O2 radical, isoprene derived peroxy radical (ISOPO2) and monoterpene derived peroxy radical (MONOTERPO2) by OH can contribute up to 25%, 15% and 50% to the total RO2 loss, respectively. The changes in RO2 reactivity influence the global abundances of organic alcohols (ROH) which are important species due to their crucial impact on air quality. The ROOOH generate secondary organic aerosol (SOA) of up to 0.05 mu g m-3 which affects the Earth's radiation budget because of enhancing modelled organic aerosol by up to 5% and 2000% on land surfaces and the remote tropical oceans, respectively.