We present an analysis of ozone (O₃) photochemistry observed by aircraft measurements of boreal biomass burning plumes over eastern Canada in the summer of 2011. Measurements of O₃ and a number of key chemical species associated with O₃ photochemistry, including non-methane hydrocarbons (NMHCs), nitrogen oxides (NO_x) and total nitrogen containing species (NO_y), were made from the UK FAAM BAe-146 research aircraft as part of the "quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites" (BORTAS) experiment between 12 July and 3 August 2011. The location and timing of the aircraft measurements put BORTAS into a unique position to sample biomass burning plumes from the same source region in Northwestern Ontario with a range of ages. We found that O₃ mixing ratios measured in biomass burning plumes were indistinguishable from non-plume measurements, but evaluating them in relationship to measurements of carbon monoxide (CO), total alkyl nitrates (ΣAN) and the surrogate species NO_z (= NO_y-NO_x) revealed that the potential for O₃ production increased with plume age. We used NMHC ratios to estimate photochemical ages of the observed biomass burning plumes between 0 and 10 days. The BORTAS measurements provided a wide dynamic range of O₃ production in the sampled biomass burning plumes with ΔO₃/ΔCO enhancement ratios increasing from 0.020 ± 0.008 ppbv ppbv⁻¹ in plumes with photochemical ages less than 2 days to 0.55 ± 0.29 ppbv ppbv⁻¹ in plumes with photochemical ages greater than 5 days. We found that the main contributing factor to the variability in the ΔO₃/ΔCO enhancement ratio was ΔCO in plumes with photochemical ages less than 4 days, and that was a transition to ΔO₃ becoming the main contributing factor in plumes with ages greater than 4 days. In comparing O₃ mixing ratios with components of the NO_y budget, we observed that plumes with ages between 2 and 4 days were characterised by high aerosol loading, relative humidity greater than 40%, and low ozone production efficiency (OPE) of 7.7 ± 3.5 ppbv ppbv⁻¹ relative to ΣAN and 1.6 ± 0.9 ppbv ppbv⁻¹ relative to NO_z. In plumes with ages greater than 4 days, OPE increased to 472 ± 28 ppbv ppbv⁻¹ relative to ΣAN and 155 ± 5 ppbv ppbv⁻¹ relative to NO_z. From the BORTAS measurements we estimated that aged plumes with low aerosol loading were close to being in photostationary steady state and O₃ production in younger plumes was inhibited by high aerosol loading and greater production of ΣAN relative to O₃. The BORTAS measurements of O₃ photochemistry in boreal biomass burning plumes were found to be consistent with previous summertime aircraft measurements made over the same region during the Arctic Research of the Composition of the Troposphere (ARCTAS-B) in 2008 and Atmospheric Boundary Layer Experiment (ABLE 3B) in 1990.

Airborne measurements of biomass burning organic aerosol (BBOA) from boreal forest fires reveal highly contrasting properties for plumes of different ages. These measurements, performed using an Aerodyne Research Inc. compact time-of-flight aerosol mass spectrometer (C-ToF-AMS) during the BORTAS (quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites) experiment in the summer of 2011, have been used to derive normalised excess organic aerosol (OA) mass concentrations (ΔOA / ΔCO), with higher average ratios observed closer to source (0.190±0.010) than in the far-field (0.097±0.002). The difference in ΔOA / ΔCO between fresh and aged plumes is influenced by a change in dominant combustion conditions throughout the campaign. Measurements at source comprised 3 plume interceptions during a single research flight and sampled largely smouldering fires. Twenty-three interceptions were made across four flights in the far-field, with plumes originating from fires occurring earlier in the campaign when fire activity had been more intense, creating an underlying contrast in emissions prior to any transformations associated with aging. Changing combustion conditions also affect the vertical distribution of biomass burning emissions, as aged plumes from more flaming-dominated fires are injected to higher altitudes of up to 6000 m. Proportional contributions of the mass-to-charge ratio (m/z) 60 and 44 peaks in the AMS mass spectra to the total OA mass (denoted f₆₀ and f₄₄) are used as tracers for primary and oxidised BBOA, respectively. f₄₄ is lower on average in near-field plumes than those sampled in the far-field, in accordance with longer aging times as plumes are transported a greater distance from source. However, high levels of ΔO₃ / ΔCO and −log(NO_x / NO_y) close to source indicate that emissions can be subject to very rapid oxidation over short timescales. Conversely, the lofting of plumes into the upper troposphere can lead to the retention of source profiles after transportation over extensive temporal and spatial scales, with f₆₀ also higher on average in aged plumes. Evolution of OA composition with aging is comparable to observations of BB tracers in previous studies, revealing a consistent progression from f₆₀ to f₄₄. The elevated levels of oxygenation in aged plumes, and their association with lower average ΔOA / ΔCO, are consistent with OA loss through evaporation during aging due to a combination of dilution and chemical processing, while differences in combustion conditions throughout the campaign also have a significant influence on BBOA production and composition.

Aerosol chemical composition was found to influence nighttime atmospheric chemistry during a series of airborne measurements in northwestern Europe in summer conditions, which has implications for regional air quality and climate. The uptake of dinitrogen pentoxide, γ (N₂O₅), to particle surfaces was found to be modulated by the amount of water content and ammonium nitrate present in the aerosol. The conditions prevalent in this study suggest that the net uptake rate of N₂O₅ to atmospheric aerosols was relatively efficient compared to previous studies, with γ (N₂O₅) values in the range 0.01–0.03. This is likely a consequence of the elevated relative humidity in the region, which promotes greater aerosol water content. Increased nitrate concentrations relative to particulate water were found to suppress N₂O₅ uptake. The results presented here contrast with previous ambient studies of N₂O₅ uptake, which have generally taken place in low-nitrate environments in the USA. Comparison of the N₂O₅ uptake derived from the measurements with a parameterised scheme that is based on the ratio of particulate water to nitrate yielded reasonably good agreement in terms of the magnitude and variation in uptake, provided the effect of chloride was neglected. An additional suppression of the parameterised uptake is likely required to fully capture the variation in N₂O₅ uptake, which could be achieved via the known suppression by organic aerosol. However, existing parameterisations representing the suppression by organic aerosol were unable to fully represent the variation in N₂O₅ uptake. These results provide important ambient measurement constraint on our ability to predict N₂O₅ uptake in regional and global aerosol models. N₂O₅ uptake is a potentially important source of nitrate aerosol and a sink of the nitrate radical, which is the main nocturnal oxidant in the atmosphere. The results further highlight the importance of ammonium nitrate in northwestern Europe as a key component of atmospheric composition in the region.

Micro- and nano-plastics (MNPLs) can move along the food chain to higher-level organisms including humans. Three significant routes for MNPLs have been reported: ingestion, inhalation, and dermal contact. Accumulating evidence supports the intestinal toxicity of ingested MNPLs and their role as drivers for increased incidence of colorectal cancer (CRC) in high-risk populations such as inflammatory bowel disease (IBD) patients. However, the mechanisms are largely unknown. In this review, by using the leading scientific publication databases (Web of Science, Google Scholar, Scopus, PubMed, and ScienceDirect), we explored the possible effects and related mechanisms of MNPL exposure on the gut epithelium in healthy conditions and IBD patients. The summarized evidence supports the idea that oral MNPL exposure may contribute to intestinal epithelial damage, thus promoting and sustaining the chronic development of intestinal inflammation, mainly in high-risk populations such as IBD patients. Colonic mucus layer disruption may further facilitate MNPL passage into the bloodstream, thus contributing to the toxic effects of MNPLs on different organ systems and platelet activation, which may, in turn, contribute to the chronic development of inflammation and CRC development. Further exploration of this threat to human health is warranted to reduce potential adverse effects and CRC risk.

This paper reports measurements of land–atmosphere fluxes of sensible and latent heat, momentum, CO ₂ , volatile organic compounds (VOCs), NO, NO ₂ , N ₂ O and O ₃ over a 30 m high rainforest canopy and a 12 m high oil palm plantation in the same region of Sabah in Borneo between April and July 2008. The daytime maximum CO ₂ flux to the two canopies differs by approximately a factor of 2, 1200 mg C m ⁻² h ⁻¹ for the oil palm and 700 mg C m ⁻² h ⁻¹ for the rainforest, with the oil palm plantation showing a substantially greater quantum efficiency. Total VOC emissions are also larger over the oil palm than over the rainforest by a factor of 3. Emissions of isoprene from the oil palm canopy represented 80 per cent of the VOC emissions and exceeded those over the rainforest in similar light and temperature conditions by on average a factor of 5. Substantial emissions of estragole (1-allyl-4-methoxybenzene) from the oil palm plantation were detected and no trace of this VOC was detected in or above the rainforest. Deposition velocities for O ₃ to the rainforest were a factor of 2 larger than over oil palm. Emissions of nitrous oxide were larger from the soils of the oil palm plantation than from the soils of the rainforest by approximately 25 per cent. It is clear from the measurements that the large change in the species composition generated by replacing rainforest with oil palm leads to profound changes in the net exchange of most of the trace gases measured, and thus on the chemical composition of the boundary layer over these surfaces.