Pollution derived from car tires is of growing research interest due to its apparent omnipresence in the urban environment and its associated toxicity. Studies have focused largely on the occurrence of these tire materials, deemed tire wear particles (TWPs), and their associated chemicals in the aquatic environment. However, less attention has been paid to atmospheric TWPs, which can remain airborne and be transported over long distances. In addition, there are few studies pertaining to the gaseous contaminants originating from tire wear, creating a significant knowledge gap. This review aims to summarize the current state of knowledge surrounding atmospheric tire wear pollution by detailing relevant studies conducted under both laboratory and ambient environmental conditions. Organic chemicals that are associated with this form of pollution, including diphenylamine antioxidants, phthalates, benzothiazole, benzotriazoles, and alkylphenols were highlighted for their potential implications for air. While a number of studies have investigated oxidation in aquatic environments, the current review highlights a clear absence of oxidation product information relevant to air. There is also a critical research gap surrounding the physico-chemical properties of these potential atmospheric pollutants. As a result, the environmental behaviour and fate of these contaminants are largely unknown. Based on these knowledge gaps, we propse recommendations for future work to advance this area of research.

This study presents a method for “downscaling” aggregated global emissions of CO, NOₓ, and PM₂.₅ based on georeferenced information (spatial proxies). We distribute ECLIPSE-CLE emissions for Quito, Ecuador, in 2015 and 2017. The study area is a grid of 0.5 × 0.5 km² cells over a 110 × 110 km² area. The emission sectors (proxies in parenthesis) are agricultural (land-use maps), domestic (land-use and population density), energy, industry, and waste disposal (point source location from local inventory), and transport (population, vehicle traffic, and road density). Emission distribution quality is satisfactorily evaluated (graphically and statistically) by implementing them in the UBM model and comparing modeled concentrations with observations. This study also explores an alternative proxy set-up for main road emissions based on road density, which, for some modeling sites, results in a better agreement with the observations. Finally, this methodology is applied for comparing air pollution due to two urban growth types for Quito in 2040: sprawl and densification. Both scenarios lead to lower concentrations than in 2017, except for O₃. Although the two scenarios attain similar concentrations, urban sprawl presents, in general, noticeably higher values for NOₓ and NO₂.

In some international cities, winter air pollution can manifest into a local-scale brown air pollution haze which has been associated with negative health outcomes. Land-sea breezes are known to impact urban air quality through the recirculation of air pollution and the formation of internal boundary layers (IBLs). However, research into land-sea breezes has primarily focused on summer air pollution and little is known about the influence of land-sea breezes on local-scale winter brown haze. Using continuous data (including surface meteorology, surface air quality, satellite-derived sea surface temperatures, and ceilometer-derived boundary-layer depths) observed over seven winters from 2013 to 2019, we present a novel investigation of the influence of land-sea breezes on brown haze in Auckland, New Zealand. Severe brown haze days are significantly more likely to coincide with a land-sea breeze circulation simultaneously occurring at both the east and west coasts when compared with days on which brown haze is expected but not observed (based on favourable meteorology and high surface air pollution levels). Both severe brown haze and high surface level PM₂.₅ concentrations (previously associated with the presence of brown haze) are found to be associated with a high degree of horizontal recirculation at Auckland's east coast. No relationship is found between the occurrence of sea-breeze-induced IBLs and the formation of brown haze. The results presented in this study offer insights into the physical mechanisms that influence the formation and persistence of local-scale winter brown haze in a complex coastal setting with correspondingly complex land-sea breezes.

Understanding and quantifying the influence of volatile organic compounds (VOCs) on ozone and secondary organic aerosol formation is essential for better prediction/estimation of these products. A total of 9 VOCs along with surface ozone were measured during the year 2019 at Pune (India) location. The ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) estimations are compared for 2 methods-using measured VOC concentrations and using their photochemical initial concentrations (PIC). The OFP and SOAFP estimated based on the measured VOC concentrations provide an incomplete understanding of these 2 formation processes. This is mainly because measured VOCs don't account for the photochemical losses that compounds undergo from the source to the receptor. The PIC values of VOCs have been estimated in this study to highlight the importance of considering the photochemical losses. For example, the PIC value of highly reactive compound, isoprene, was found to be 152% higher (1.48 ppbv) than its measured value (0.59 ppbv). The resultant total OFP estimate based on PIC values of all the VOCs was found to be 53.30 ± 35.02 ppbv as compared to 45.99 ± 29.35 ppbv obtained from measured VOCs. Based on k-means clustering analysis, it was found that the highest ozone formation was favored under transition regime chemistry when PIC values were considered. The average total SOAFP based on PIC values was found to be 1.32 ± 1.40 ppbv, while it was 1.17 ± 1.18 ppbv for measured VOCs. The aromatics contributed to over 90% of total SOAFP estimated for the region.

Ambient concentrations and sources of non-Methane Hydrocarbons (NMHCs) with 6–9 carbon atoms were investigated at an industrialized coastal location within the Port of Piraeus in Greece. Measurements were performed for a yearlong period during 2019 by means of an automated gas chromatograph with flame ionization detector (GC-FID). N-Hexane registered the highest annual mean concentration, followed by toluene and benzene, whereas all compounds presented important day to day variability, with an enhancement in summer. The seasonal diurnal cycles were characterized by strong morning peaks, especially in summer. The night-time maxima were less pronounced during the warm period, by almost 50% relative to the morning ones. On the contrary, during winter night-time, the combined impact of emissions and the shallow boundary layer was reflected on the night-time peaks. The area seems to be affected mainly by local land emission sources, whereas temperature possibly triggers evaporation processes, as indicated by comparisons with nearby traffic and urban background sites. The enhanced NMHCs concentration, in spite of increased ventilation coefficients during the summer, indicated again the impact of local emission sources. This was also highlighted by means of Positive Matrix Factorization (PMF) modeling. Three PMF factors were identified, quantified and supported by supplementary seasonal runs during short-term campaigns. Fugitive emissions were recognized as the main source, contributing more than 70% of total NMHCs year-round, while the input of emissions associated with traffic and diesel combustion was almost equal (13% and 15%, respectively).

In this paper, we investigate the footprint of the operation of Athens International Airport in loads of air pollutants emitted during the Landing-Take Off phase of incoming and outgoing flights. This part of the flight has the distinctive characteristic that it operates in the human environment, at low altitudes, so it directly affects the air quality at the airport and its surroundings by changing the total amounts of air pollutants involved. The present survey covers the period 2002–2019 and only civil aircrafts flights have been considered. In particular, the concentrations mono-nitrogen oxides (NOX), carbon monoxide (CO), carbon dioxide (CO₂), unburnt hydrocarbons (HC) and total Particulate Matter (PM) consisting of volatile organic PM, volatile sulphuric PM and non-volatile PM have been studied. According to the results obtained more than 6500 kt of CO₂, almost 28 kt of NOX, about 18 kt of CO, almost 1.5 kt of HC and 0.3 kt of PMₜₒₜₐₗ have been released into the atmosphere during the total operating time of the airport. Actions related to the conduct of new measurements of air pollutants are aimed which point to the reduction of their impacts in the coming years.

Based on the ground-level observed NO₂ concentration, satellite-observed NO₂ column concentration from the Ozone Monitoring Instrument (OMI) and meteorological parameters, we comprehensively consider the seasonal and regional differences in the relationship between NO₂ column concentration and measured NO₂ concentration and establish a two-stage combined ground NO₂ concentration estimation (TSCE-NO₂) model using a support vector machine for regression (SVR) and a genetic algorithm optimized back propagation neural network (GABP). On this basis, the spatial-temporal variation in the modelled ground-level NO₂ concentration over China during the period of 2005–2019 was analysed. The results show that the TSCE-NO₂ model proposed in this study provides a reliable estimation of the modelled ground-level NO₂ concentration over China, effectively filling the spatial and temporal gaps in China's air quality ground monitoring network (the model's correlation coefficient, R, is 0.92, the mean absolute error, MAE, is 3.62 μg/m³, the mean square percentage error, MSPE, is 0.72%, and the root-mean-square error, RMSE, is 5.93 μg/m³). The analysis results of the spatial and temporal variation indicate that (1) the perennial ground-level NO₂ concentration over China is high in the eastern area and low in the western area, and the high values are mainly distributed along the northern coast, the eastern coast, the middle reaches of the Yangtze River, the middle reaches of the Yellow River, the Pearl River Delta and the Sichuan Basin. (2) The modelled ground-level NO₂ concentrations over China are highest in winter, followed by those in autumn and spring, and they are lowest in summer. Before 2011, the ground-level NO₂ concentration over China increased at a rate of 0.348 ± 0.132 μg/(m³∙a) but decreased at a rate of 0.312 ± 0.188 μg/(m³∙a) after 2011. (3) From 2011 to 2019, measures such as energy savings and emission reductions alleviated NO₂ pollution on the premise of ensuring sustained China's GDP growth.

Land-use and land-cover changes due to urban expansion is recognized as one of the crucial factors affecting carbon dioxide emissions. In this study, the land conversion effects on soil CO₂ fluxes associated with temperate re-established grasslands within the Forest Botanical Garden found on an anthropogenic landform were investigated. The present work analyses the capabilities and requirements of the CALPUFF Lagrangian puff air quality modelling system to simulate the spatial distribution of ecosystem respired CO₂ in the urban domain. The results are validated against the available observations of CO₂ fluxes in the urban environment using the closed-chamber method with the measurements of the stable carbon isotope ratio (δ¹³C) of daytime soil-respired CO₂. The isotope mass balance partitioning approach was applied to distinguish biogenic portions of CO₂ from the admixture of atmospheric air.The spatial and temporal amplitude of the simulated CO₂ concentrations from the CALPUFF model showed considerable agreement with the tracer measurements of the biogenic CO₂ component in the near-ground air (0.25 m). In most cases, however, the CALPUFF predictions of ecosystem-derived CO₂ showed a general tendency toward considerable underestimation of real concentration levels. Such discrepancies are related to the difficulties associated with the optimization of biospheric CO₂ flux and uptake from ecosystems by means of local-scale modelling. The modelled results implied that the CALPUFF performance in the dispersion simulation of CO₂ concentrations within the urban ecosystems is very sensitive to the initial meteorological conditions, grid resolution, measurement timescale, and the calculated gas flux rate from soils. A significant negative correlation was found between hourly values of the average modelled CO₂ and observed wind speed during the entire study campaign (r = −0.58 and ρ = −0.82 for Pearson and Spearman statistics, respectively, p < 0.05). Moreover, analysis of the impact of the deposition parameters on changes in the atmospheric concentration of carbon dioxide indicated significant dependency of the temporal CO₂ distribution patterns on the precipitation-based events. According to the obtained estimates, the wet deposition rate during rain events was approximately two orders higher than the average dry deposition flux.Overall, the present case study indicates that the CALPUFF model has a rather acceptable predictive ability. A better agreement of model predictions and all field measurements, however, require further studies of CO₂ exchange between the ecosystem and atmosphere and understanding where they need to be improved.

Chronic atmospheric nitrogen (N) deposition could influence the functioning of ecosystems as well as their biodiversity. However, N deposition in urban forest ecosystems, especially natural evergreen broad-leaved forests, is not well known. In this study, the concentrations and fluxes of dissolved inorganic N (DIN) and dissolved organic N (DON) in bulk deposition, throughfall, and stemflow were assessed in an urban evergreen broad-leaved forest site over three years, in order to clarify the characteristics of N deposition. At the study site, bulk DIN deposition was 3.7 kg N ha⁻¹ year⁻¹ (1.5 kg N ha⁻¹ year⁻¹ for NH₄–N and 2.2 kg N ha⁻¹ year⁻¹ for NO₃ + NO₂–N), which is the same level as that found in rural areas. In contrast, 6.5 kg N ha⁻¹ year⁻¹ for bulk DON deposition contributed to 66% of the bulk N deposition, which suggests the importance of bulk DON deposition in Japanese forest ecosystems. Passing through the tree canopy, DIN was enriched by 8.8 kg N ha⁻¹ year⁻¹ (3.7 kg N ha⁻¹ year⁻¹ for NH₄–N and 5.1 kg N ha⁻¹ year⁻¹ for NO₃ + NO₂–N) and DON was enriched by 1.5 kg N ha⁻¹ year⁻¹ as net throughfall in the evergreen broad-leaved forest. This reveals that dry deposition of DIN dominates the total DIN deposition onto the urban forest floor, compared to that found in the rural areas, due to the non-negligible N emissions from outside and possibly because of the evergreen broad-leaved forest's greater ability to capture N.

Well integrity failure resulting in migration of natural gas outside of the surface casing can cause atmospheric greenhouse gas emissions and groundwater quality impacts from existing and historic energy wells. Spatial and temporal variability in gas migration can result in errors in detection (i.e., presence/absence) and efflux estimations. This field-based case study used automated dynamic closed chambers to record repeated (~every 18 min) CO₂ and CH₄ efflux measurements over a two-week period around a single petroleum production well in Alberta, Canada. Long-term efflux measurements supplemented soil gas compositional and isotopic characterization, along with surface concentration measurements. Effluxes were spatially concentrated around the wellhead and only occasionally detectable more than a few meters away. Estimated total emissions attributable to gas migration ranged from 48 to 466 g CH₄ d⁻¹ (or 0.07–0.7 m³ CH₄ d⁻¹). Methane effluxes and concentrations were temporally variable on second-to-hourly and diel scales. Multivariate stepwise regression analysis indicates that multiple meteorological factors, particularly wind speed and air temperature, were related to the temporal variability. Despite temporal variability, elevated concentrations and effluxes were consistently detectable around the well. Major soil gas composition suggests that gas migration near the wellhead causes advective displacement of soil gas, while more distal measurements are indicative of episodic and diffusion-dominated transport. Values of ¹³C–CO₂ and ¹³C–CH₄ samples were consistent with CH₄ oxidation within the unsaturated zone. Although these results reflect a single well, the findings are salient to gas migration detection and emission estimation efforts.