Open biomass burning impacts air quality through direct emissions of fine particulate matter (PM2.5) and its role in secondary PM2.5 formation. Here the interest is in the long distance and cumulative influences of biomass burning on annual mean concentrations of PM2.5 in a country far removed from major biomass burning regions: the UK. A novel, globally nested setup of the EMEP4UK atmospheric chemistry transport model is used to isolate contributions to UK PM2.5 from global biomass burning activity. Long-range influences are found to be considerable, with 0.99 & micro;gm-3 of UK-averaged PM2.5 in 2019 being conditional on biomass burning emissions. Of this, 97 % and 73 % are associated with biomass burning outside the UK and outside the model's European domain, respectively - notably from Russia, Asia and boreal North America - which highlights the importance of boundary conditions on regional modelling setups. The simulations suggest some influences of biomass burning have lags of several weeks. The long-range component is enhanced by the role of biomass burning in secondary aerosol formation (58 % of PM2.5 conditional on biomass burning), of which 55 % is organic; the inorganic component (mainly ammonium nitrate) derives from increased oxidation of local emissions, which may be mitigated through local emissions reductions. The PM2.5 conditional on biomass burning is highly policy relevant for the UK, constituting (for 2019) 20 % of the current WHO target and 10 % of the contribution from all sources. This relative contribution is likely to increase as anthropogenic PM2.5 declines and as climate change increases northern-hemispheric extratropical biomass burning.

Microbial uptake in soils is the dominant natural sink of atmospheric hydrogen (H2); however, the environmental controls governing this process remain poorly constrained across different soil types and land uses. This study investigates H2 fluxes with a diverse set of soils using controlled laboratory incubations designed to isolate the effects of soil moisture, soil physical properties, carbon pools, pH, and temperature. Topsoils from 11 sites were sieved, repacked, and subjected to a moisture gradient from saturation to near-dryness, with H2 fluxes regularly measured. Across all soils, moisture was the primary control of H2 uptake. Uptake initially increased as soils dried from saturation, peaked at intermediate moisture levels (10 to 40% water-filled pore space), and then declined again under both saturated and near-dry conditions. Organic content-rich systems behaved differently to mineral soils. Peatland soil showed exceptionally strong H2 uptake across a wider moisture range, driven by its porous structure and large dissolved organic carbon (DOC) pool. When included in regression models, DOC content emerged as a major predictor of flux, contributing significantly to an overall model explanatory power of R2 = 0.51 when paired with other variables. Investigations revealed that forest litter acted as a strong H2 sink, with uptake an order of magnitude higher than soils (by mass) and remained active even at sub-zero temperatures. These results demonstrate that H2 uptake is strongly regulated by soil physical structure and moisture in mineral soils, but also by labile carbon and organic-layer properties in high-carbon environments. The findings highlight the importance of explicitly representing peatlands, the availability of labile carbon pools, and surface organic layers in models of the global H2 budget and emphasise the need for more field measurements in carbonrich and understudied ecosystems.

Delhi experiences some of the highest levels of fine particulate matter (PM2.5) pollution among megacities worldwide. Here, we integrated radiocarbon (14C) analysis with organic molecular tracers to quantify the sources of carbonaceous aerosols in Delhi. Through time-resolved seasonal and diurnal PM2.5 sampling at two representative urban sites and using 14C as an unambiguous tracer, we provide robust quantitative constraints on source contributions. We found that fossil fuel combustion is the dominant contributor, accounting for 62-65 % of organic carbon and 64-66 % of elemental carbon in PM2.5. Crucially, primary organic carbon from fossil fuels (POCFF) constituted the largest fraction of PM2.5 organic carbon (31-44 %). Its contribution peaked in the post-monsoon season, driven mainly by traffic emissions and coal combustion. Secondary organic carbon from fossil sources (SOCFF), biomass burning (OCBB), and cooking emissions (OCCK) contributed 21-29 %, 10-18 % and 3-7 % of PM2.5 organic carbon, respectively. Furthermore, comparisons with Positive Matrix Factorization (PMF) results suggest that conventional methods may overestimate the biomass burning contribution, underscoring the value of the 14C-based approach for accurate apportionment in this complex environment. This study underscores the critical need to reduce fossil fuel reliance and accelerate the shift toward clean energy infrastructure to effectively combat carbonaceous aerosol pollution in Delhi.

The lack of energy balance closure in Eddy-Covariance (EC) measurements is a well-known, still unresolved challenge in micrometeorology, with energy balance closure (EBC) rates typically ranging between 60% and 80%. While numerous hypotheses have been proposed to explain this imbalance, the relative contributions of neglected energy storage terms, data quality and flux processing options remain insufficiently disentangled. Using standardized ICOS and NEON datasets, we show that a significant portion of the observed energy imbalance can be attributed to overlooked or inconsistently handled energy components and turbulent flux quality control. Using data drawn from 84 sites, we show that comprehensive energy accounting-including soil heat flux, storage terms (soil, air, biomass), photosynthetic energy demand, and strict quality filtering of turbulent fluxes-improved EBC by 16% on average, with site-specific gains up to 40%. However, we also identify a persistent residual imbalance that is unlikely to be resolved through methodological refinements or additional measurements alone, pointing to fundamental physical processes that are not accounted for in the standard measurement and processing. We argue that this unresolved imbalance should be explicitly acknowledged and bounded, rather than implicitly absorbed into correction schemes, and we outline practical guidance for diagnosing and interpreting EBC in standardized flux networks. This perspective evaluates methodological advances and residual uncertainties, providing an actionable framework for the appropriate use of EC energy fluxes in carbon, water, and climate research.

The Russian invasion of Ukraine has disrupted crop exports and global food security, overshadowing critical nutrient asymmetry and the associated environmental risks. Here we demonstrate that following nutrient shortages after independence in 1991, fertilizer use increased over 2000-2021, but has decreased sharply following the invasion in early 2022. Input-output balances of nitrogen (N), phosphorus (P) and potassium (K) for staple crops (wheat, maize and sunflower) highlight soil P and K mining since 1991, increasing N surpluses during 2000-2021 and large NPK deficits since the war began in 2022. Based on analysis of five scenarios for 2030, we show how an Integrated Nutrient Management Plan for Ukraine combining manure recycling, precision fertilization and legume expansion is urgently needed, and would maintain crop productivity, significantly reduce nutrient surpluses and improve nutrient use efficiencies up to 80-89%, substantially curtailing environmental pollution and soil degradation.

Emissions of hydrogen (H2) gas from human activities are associated with indirect climate warming effects. As the hydrogen economy expands globally (e.g. the use of H2 gas as a fuel), the anthropogenic release of H2 into the atmosphere is expected to rise rapidly as a result of increased leakage. The dominant H2 removal process is uptake into soils; however, removal mechanisms are poorly understood, and the fate and impact of increased H2 emissions remain highly uncertain. Fluxes of H2 within soils are rarely measured, and data to inform global models are based on few studies. This study presents soil H2 fluxes from two field sites in central Scotland, a managed grassland and a planted deciduous woodland, with flux measurements of H2 covering full seasonal cycles. A bespoke flux chamber measurement protocol was developed to deal with the fast decline in headspace concentrations associated with rapid H2 uptake, in which exponential regression models could be fitted to concentration data over a 7 min enclosure time. We estimate annual H2 uptake of -3.1±0.1 and -12.0±0.4 kg H2 ha−1 yr−1 and mean deposition velocities of 0.012±0.002 and 0.088±0.005 cm s−1 for the grassland and woodland sites, respectively. Soil moisture was found to be the primary driver of H2 uptake at the grassland site, where the high silt/clay content of the soil resulted in anaerobic conditions (near zero H2 flux) during wet periods of the year. Uptake of H2 at the forest site was highly variable and did not correlate well with any localised soil properties (soil moisture, temperature, total carbon and nitrogen content). It is likely that the high silt/clay content of the grassland site (55 % silt, 20 % clay) decreased aeration when soils were wet, resulting in poor aeration and low H2 uptake. The well-drained forest site (60 % sand) was not as restricted by exchange of H2 between the atmosphere and the soil, showing instead a large variability in H2 flux that is more likely to be related to heterogeneous factors in the soil that control microbial activity (e.g. labile carbon and microbial densities). The results of this study highlight that there is still much that we do not understand regarding the drivers of H2 uptake in soils and that further field measurements are required to improve global models.

This research delves into the spatial distribution of 17 elements (Al, B, Ba, Bi, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb, Sr, Te, and Zn) within the <20 mu m size fraction of road dust samples collected from 177 locations within 65 grid cells (each 5 x 5 km(2)) throughout Delhi in February 2021. Notably, Fe and Al emerge as the predominant elements in the road dust samples. Using Principal Component Analysis (PCA), Absolute Principal Component Score (APCS), and Multiple Linear Regression (MLR) techniques, it is observed that crustal sources (58%), non-exhaust vehicular emissions (21%), and two distinct industrial origins (2% and 19%) are major contributors to the road dust composition. Bi and Te exhibited the highest geo-accumulation indices, indicating significant pollution levels, with notably high contamination factors, surpassing a contamination degree of 24. Elements like Cd posed the highest potential ecological risk, dominating 95% of the risk assessment. The hazard index analysis highlighted that urban populations, especially children, face the greatest risk through ingestion, followed by dermal exposure, and least through inhalation. Notably, Cd, Pb, Cr, and Ni were identified as elements posing a very high carcinogenic risk to the general populace.

Volatile organic compounds (VOCs) together with nitrogen oxides contribute to the formation of ground-level ozone as well as PM2.5 pollution through secondary organic aerosol formation, with adverse effects on human health and environment. Researchers have mainly focused on quantifying VOC emissions from plant canopies and their controls, leading to improvements in atmospheric chemistry models (Jimenez et al., 2009). However, much less attention has been spent on quantifying dry deposition of primary and secondary VOCs to surfaces, with most models often using deposition rates extrapolated from SO2 (as a proxy of a water-soluble gas of limited reactivity) and O3 (as a proxy of an insoluble reactive gas), making uncertain assumptions on the relative behaviour of key VOCs (Wesely, 2007). To address this, we conducted the first systematic, measurement-based investigation into VOC dry deposition as part of the ‘Dry Deposition Processes of VOCs’ project funded by Natural Environment Research Council. The overarching aim of the study was to reduce uncertainty in atmospheric chemistry models by developing parameterisations for the dry deposition of VOCs. The preliminary results of our laboratory study on plant fumigation with methacrolein (MACR), among other selected VOCs, are presented here.An automated dynamic gas-exchange chamber system was developed to expose test plants to specific VOCs at various concentrations under controlled conditions. Overall, six plant species (see below) were tested with each experiment lasting four days: one day to observe background emissions and three days with VOC fumigation at 20, 15 and 10 °C. Three levels of relative humidity (RH) were applied during day and night times, being fumigated with five concentrations of VOCs within each RH level. In total, eleven VOCs were selected for fumigation: water-insoluble (isoprene, benzene, toluene, xylene, a-pinene) and water-soluble (methanol, acetonitrile, acetaldehyde, acetone, acetic acid and MACR). VOCs were measured using a proton transfer reaction instrument equipped with time-of-flight mass spectrometer (PTR-Qi-TOF). Fluxes were calculated based on concentration difference between blank and measurement chambers and then normalized by the corresponding plant leaf area indices.MACR appears to be ‘valuable’ VOC to study dry deposition as it is not typically emitted by plants but is an important first-order product of isoprene oxidation in the atmosphere. Nevertheless, minor MACR emissions have been reported, suggesting that oxidation may also take place within leaves (Fares et al., 2015). The deposition velocity of MACR was found to increase with RH, and larger deposition velocities were consistently observed during the daytime compared to the night. This diurnal dependence indicates either stomatal control or photochemical processes, or a combination of the two, were present under daylight conditions. However, this varied substantially across tested plants being ranked in the following order Pinus sylvestris > Hedera sp. > Picea glauca > Betula sp. > Tsuga heterophylla > Ilex aquifolium. At all times, MACR compensation points were found to be negligible (near zero) or even negative, suggesting minor or no impact on deposition rates.These findings are enhancing our understanding of VOC deposition and will inform the development of new parameterizations for atmospheric chemistry models.

Deposition of reactive nitrogen (Nr) onto sensitive habitats in exceedance of Critical Load (CL) thresholds can drive biodiversity loss and affect ecosystem function. Nr deposition is a highly complex process that is difficult to measure and model, leading to large uncertainties. We assess the implications for policy development and target setting of the large range in estimates provided by different modelling approaches. We considered three UK models (UKIAM, EMEP4UK, CBED), used to inform national policy and responses to the UN-ECE Air Convention. We used a scaling method to project the range in current estimates to future scenarios, and a risk-based approach to provide a probabilistic assessment of exceedances. We considered two future scenarios, a 2040 baseline and a 2040 high ambition technological measures scenario, in relation to a 2018 baseline. The 2018 baseline CL exceedances are highly dependent on the model used - Average Accumulated Exceedance of 1.3-9.1 kg.N.ha-1.yr-1 across all habitats. The relative reduction in exceedances for future scenarios also depends on the model, with a range of 30-66% achieved by 2040 for the high ambition scenario, posing a challenge for target setting. Despite this, it's clear that a much greater level of ambition is required to protect the majority of habitat areas. Our risk-based approach shows that implementing only technological measures is likely to leave most areas in exceedance in 2040. This uncertainty in the assessment of Nr deposition and the benefits of abatement measures poses a challenge for policy development that is not unique to the UK.

Road transport NO x emissions in many high-income countries have steadily reduced due to improved exhaust after-treatment technology. However, ambient concentrations of NO2, O3 and PM2.5 continue to exceed World Health Organization guidelines in many cities globally. The megacity of London has taken an international lead in mobility interventions through the use of low-emission zones. Using long-term air pollution flux measurements made from a communications tower, we show that the largest source of NO x emissions in central London has transitioned from road transport to space heating. Observations and supporting consumption/mobility data indicated that natural gas combustion in boilers was responsible for 72 +/- 17% of NO x emissions in the measurement footprint (average years 2021-2023). Road transport has dominated air quality thinking on NO2 for many decades. However, in urban environments that are reliant on natural gas, building heating may now be an effective sector to prioritize for further NO x emissions intervention. With system-wide changes in the heat and power sector expected in the coming decades to achieve decarbonisation pledges, we project that very low urban emissions of NO x are achievable. The trajectory will, however, depend on choices made around urban buildings and their associated infrastructure and whether low-carbon fuel combustion or electrification pathways are chosen. We estimate a damage cost penalty of up to 600 pound M in the U.K. should hydrogen combustion replace natural gas for heating rather than technologies such as heat pumps.

Black carbon (BC) is a significant environmental health and climate forcing concern. Direct measurement of BC fluxes using eddy covariance can quantify emissions and identify sources. Previous studies have examined urban BC emissions in highly polluted countries such as China and India, but to date no equivalent research has been done in the UK and Europe. Here, we present black carbon flux data from a single particle soot photometer (SP2) deployed in an eddy covariance system at the BT (formerly British Telecommunications) Tower in central London. Mean BC mass (number) fluxes with a size range of 60 nm to 600 nm were 6.83 ng m-2 s-1 (443 cm-2 s-1) in summer and 13.3 ng m-2 s-1 (687 cm-2 s-1) in winter, indicating relatively low BC emission when compared to Delhi, which is likely due to the introduction of the ultra-low emission zone (ULEZ) and requirements for road diesel vehicles to meet Euro 6 standards or higher. However, flux footprint analysis identified strong point sources near construction sites during winter and summer observations, which implies that non-road mobile machinery (NRMM) emissions can dominate over traffic BC emissions. This implies that tightened NRMM regulations can help future air quality in London. Observations indicate that the UK's National Atmospheric Emissions Inventory (NAEI) overestimates BC emissions by a factor of 5, although large uncertainties are expected for the combustion sector in the manufacturing industry. The estimate of traffic emissions is more accurate.

Countries in South Asia are suffering severe PM 2.5 pollution with rapid economic development, impacting human health and the environment. Whilst much attention has been given to understanding the contribution of primary emissions, the contribution of agriculture to PM 2.5 concentrations, especially from agricultural ammonia (NH3) emissions, remains less explored. Using an advanced regional atmospheric chemistry and transport modelling system (WRF-EMEP) with a new estimate of anthropogenic NH3 emissions inputs, we estimate the influence of agricultural NH3 emissions on surface PM 2.5 in South Asia and evaluate the health impacts and the economic losses attributable to PM 2.5 in 2018. Results show that WRF-EMEP can reproduce magnitudes and variations of PM 2.5 well, with a high annual mean PM 2.5 concentration that exceeds 120 mu g/m 2 and mainly appeared in the Indo-Gangetic Plain. We estimate 2,228,000 (95 % Confidence Interval: 2,052,000-2,400,000) premature deaths and US$ 596,000 (95 % CI: 549,000-642,000) million in economic losses are attributable to total ambient PM 2.5 under the current emissions. We calculate that NH3 emissions are associated with 11 % of the annual average PM 2.5 concentrations across South Asia. Changes in PM 2.5 concentrations follow a non-linear response to NH3 emissions reductions, highlighting increased efficiency with 70 %-100 % reductions in NH3 emissions reductions. We estimate that 247,000 (227,000-265,000) premature deaths and US$ 66,000 (61,000-71,000) million economic losses through this pathway can be attributed to NH3 emissions. These findings confirm that in the current NH3-rich chemical environment of South Asia, the efficiency of PM 2.5 reduction is only moderately sensitive to the reduction in intensity of NH3 emissions until emissions are cut very severely. Thus, SO2, NOx and NH3 emissions controls need to be considered jointly for greater mitigation of ambient secondary PM 2.5 in South Asia.

Open biomass burning affects many aspects of the Earth system, including atmospheric chemistry and composition. Due to its impact on human health, we focus on the contribution of biomass burning emissions to fine particulate matter (PM2.5) concentrations on a global, annual mean basis, particularly the lesser-studied secondary inorganic component. We use the EMEP MSC-W WRF atmospheric chemistry transport model to show that biomass burning leads to increased ammonium nitrate (NH4NO3) concentrations in densely populated regions not necessarily associated with large-scale fire activity. This is prominent in the eastern USA, northwestern Europe, the Indo-Gangetic Plane and eastern China, where NH4NO3 contributes between 29 and 51% to annual mean biomass burning-derived PM2.5. Pyrogenic CO and NOx (NO and NO2) emissions alter the global-scale oxidising capacity of the atmosphere, affecting how local-scale anthropogenic NOx and NH3 emissions lead to formation of NH4NO3. These teleconnections can locally increase, by up to a factor of two, the contribution of biomass burning emissions to PM2.5 concentrations, which measurements alone cannot detect. This will become relatively more important as anthropogenic sources of PM2.5 are reduced, and with potentially intensified biomass burning occurrences under climate change.

This programme examines the climate and air quality implications of transitioning from fossil fuels to hydrogen-based energy systems. It comprises three independent projects – ELGAR, HECTER and COSH-AIR – that investigate various aspects of hydrogen usage and its effects on the atmosphere. The research explores future global and UK energy scenarios, focusing on the development of hydrogen infrastructure and the potential for fugitive hydrogen emissions. It also examines the role of microbial soil processes in removing atmospheric hydrogen, as well as the impacts of hydrogen deployment on climate and air quality. This overview will provide a summary of the research undertaken and the insights gained throughout the programme.

This study presents a novel ammonia sensor using hydrothermally synthesized ZnO nanowires integrated with a mode-localized coupled resonator. The ZnO nanowires, with their high surface area, act as an efficient gas adsorption layer. The resonator's driving mechanism was optimized using finite element method (FEM) simulations, revealing that a coupled resonator pair exhibited 45.52 times higher sensitivity than a single resonator. Out-of-phase modes showed greater sensitivity than in-phase modes. Resonators R1 and R2 driven together had the lowest sensitivity, while Resonator 1, with a zinc oxide layer and driven individually, demonstrated the highest sensitivity. Additionally, the sensitivity of the coupled resonator increased with the decrease in dc bias voltage. Comprehensive materials characterization of the ZnO nanowires was conducted using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to confirm their structural and chemical properties. Fourier-transform infrared spectroscopy (FTIR) results showed that after ammonia adsorption, ZnO nanowires exhibited additional absorption bands at approximately 1430 cm (-1) , 1633 cm (-1) , and within the broad range of 3100 to 3550 cm( -1) . The sensor's gas-sensing performance was evaluated with varying ammonia concentrations, achieving a very high sensitivity of 0.0026 ppm( -1) in the 25-100 ppm range at room temperature. This design highlights the potential of integrating ZnO nanowires with coupled resonators for highly sensitive, miniaturized, low-cost sensors for environmental monitoring and safety applications.

An improved quantification of the soil sink of Hydrogen (H2) gas is required to understand the environmental implications of a future Hydrogen economy and global atmospheric models. Typically, soil microbes utilise H2 as an energy source, but we also have evidence that emission of H2 from soils is also possible via microbial processes. We present new H2 flux data from several field sites and lab studies in which a variety of soils from around the world have been measured from. These sites include agricultural and forest soils from the UK where we have preliminary data of a longer-term measurement campaign. We have developed flux chamber methodology to establish a best practice for measuring H2 flux in soils, which is radically different from typical greenhouse gas protocols. We present our work so far on the development of H2 measurement methodology and on the characterisation of the H2 soil sink in relation to soil physical & chemical properties, vegetation and climate under controlled environment conditions. We also present observations of spatial and temporal soil H2 uptake rates from sites across the UK. We highlight the importance of soil aeration and the physical barriers that strongly interfere with H2 uptake in soils, particularly the influence of high water-filled pore space which should be accounted for in future modelling efforts.

Open biomass burning has major impacts on the Earth system, including on air quality via the emission of primary fine particulate matter (PM2.5). Its effect on secondary inorganic PM2.5 formation is comparatively little investigated. Simulations with the EMEP MSC-W WRF atmospheric chemistry transport model reveal that global biomass burning emissions lead to elevated annual mean ammonium nitrate (NH4NO3) concentrations in densely populated regions where biomass burning mostly does not occur. These regions include eastern USA, northwestern Europe, the Indo-Gangetic Plain and eastern China, where NH4NO3 conditional on biomass burning emissions constitutes between 29% and 51% of the annual mean PM2.5 conditional on biomass burning emissions. Biomass burning emissions of CO, NOx (NO and NO2) and volatile organic compounds perturb the HOx (OH and HO2) cycle globally, such that there is increased oxidation of anthropogenic NOx to HNO3. This results in additional contributions to local-scale secondary NH4NO3 in areas with high emissions of anthropogenic NOx and NH3. These teleconnections increase, by up to a factor of two, the contribution of biomass burning emissions to long-term PM2.5 concentrations, which measurements alone cannot identify as an impact of biomass burning activity. This may become relatively more important as anthropogenic sources of PM2.5 are reduced and as the wildfire component of biomass burning increases under climate change.

Methanesulfonic acid (MSA) is an important product from the oxidation of dimethyl sulfide (DMS), and thus is often used as a tracer for marine biogenic sources and secondary organic aerosol. MSA also contributes to aerosol mass and potentially to the formation of cloud condensation nuclei and new particles. However, measurements of MSA at high temporal resolution in the remote Arctic are scarce, which limits our understanding of its formation, climate change impact and regional transport. Here, we applied a validated quantification method to determine the mass concentration of MSA and non-sea salt sulfate (nss-SO4) in PM2.5 in the marine boundary layer, using a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) during a research cruise to the Arctic and North Atlantic Ocean, between 55 °N and 68 °N (26th May to 23th June 2022). With this method, the concentrations of MSA in the remote Arctic marine boundary layer were determined for the first time. Results show that the average MSA concentration was 0.025±0.03 μg m-3, ranging from <0.01 to 0.32 μg m-3. The lowest MSA level was found towards the north leg of the cruise (near Sisimut (67 °N)) where was dominant influenced by air mass over sea ice from the northern polar region, and the highest MSA concentrations were observed over the Atlantic open ocean. The diurnal cycles of gas MSA, particulate MSA and nss-SO4 peaked at afternoon followed 1 hour later than that of solar radiation, which suggests that photochemical process via the OH-initiated pathway is an important mechanism for the conversion of DMS into MSA above the remote ocean. The mass ratio of MSA to nss-SO4 (MSA/nss-SO4) presents a temperature dependence, which indicates that the addition branching pathway favors MSA formation, while thermal decay of intermediate radicals could be a possible pathway for sulfate formation. Finally, we conclude the reference values of MSA/nss-SO4 for the remote marine atmosphere as 0.22-0.25 by combining air mass cluster analysis and the group classification results.

The effects of air pollution on human and animal health, and on the functioning of terrestrial ecosystems, are wide-ranging. This potentially includes the disruption of valuable services provided by flying insects (e.g. pollination and biological control). However, quantifying the extent of this disruption requires a clearer understanding of insect community responses at field-scale.By elevating diesel exhaust and ozone (O3) pollutants, individually and in combination, over two summers, we investigated the field-scale effects of air pollution on the abundance and diversity of flying insects from pan traps. We quantified which groups of insects were more at risk of air pollution-mediated decline and whether responses to air pollution were influenced by the presence of flowering plants. In addition, a common pest of Brassicaceae, the large cabbage white butterfly (Pieris brassicae L.) was used to investigate the effects on oviposition success of the two interacting air pollutants.Air pollution had the most detrimental effects on pollinators and parasitoids, compared with other insect groups, lowering their abundance by up to 48 % and 32 %, respectively. The adverse effects of O3 and diesel exhaust on pollinators occurred only when flowers were available, indicating the relative importance of floral odors compared with visual cues. Air pollutants resulted in either increased insect herbivore abundance or had no effect, potentially increasing the threat air pollution poses to food security. However, both pollutants resulted in decreased oviposition by cabbage white butterflies, which, if demonstrated to be a more ubiquitous phenomenon, may result in reduced larval pest damage.Quantifying the relative changes in composition and abundance among feeding guilds is valuable for predicting the effects of air pollution on insect communities. Of the groups identified, pollinators are likely to be at the greatest risk of air pollution-mediated decline due to their use of floral odour cues for foraging.