This paper reports the temporal variations, sources and transport characteristics of carbonaceous aerosol in Chongqing, a megacity in the Sichuan Basin. Hourly organic carbon (OC) and elemental carbon (EC) mass concentrations in PM₂.₅ were measured at an urban supersite from November 2019 to October 2020. The annual mean PM₂.₅, OC and EC concentrations (±1SD) were 38.50 ± 25.79 μg/m³, 9.03 ± 5.73 and 2.45 ± 1.47 μgC/m³, respectively. An intensive influence of biomass combustion was found during the observation period. Strong seasonality of carbonaceous aerosol with highest concentrations in winter and lowest concentrations in summer was observed. Meanwhile, two diverse pathways for secondary formation dominated in different seasons. One was highly related to gas-phase photochemical oxidation under high temperature and radiation, and another was highly related to heterogeneous reactions, while the latter was more significant, especially in winter. Diurnal and quarterly variation patterns for carbonaceous aerosol showed that the development of planetary boundary layer strongly influenced carbonaceous aerosol concentrations. Moreover, the regional sources from the northeast within the basin were identified as major contributors of the primary carbonaceous aerosol to Chongqing, while secondary components were more from local sources than regional transport. This study highlights the importance of prioritising the abatement of gaseous precursors for carbonaceous aerosol and an urgent need for the inter-regional prevention and control measures of the cities located in the Sichuan basin, especially the cities in the northeast of urban Chongqing.

This study evaluates the carcinogenic and the non-carcinogenic health risks related to non-methane volatile organic compounds (NMVOCs) and elements, dioxins, furans, dioxin-like polychlorobiphenyls, phthalates and polycyclic aromatic hydrocarbons in PM₂.₅ samples collected during a one-year field campaign in two urban industrial areas in the East Mediterranean region. The health risk was assessed for the three exposure pathways (ingestion, inhalation and dermal contact) and for different age categories (newborns, children, adolescents, and adults). The non-carcinogenic risk calculated for the different species showed that benzene and n-heptane explained 78–94% of the total hazard index (HI) for NMVOCs at both sites. The total HI for NMVOCs varied between 2.9 and 26.8 at Zouk and between 0.8 and 6.6 at Fiaa for adults and newborns respectively exceeding the recommended USEPA limit of 1 for most age categories. PM₂.₅-bound elements had values higher than the recommended USEPA limit for newborns with Mn, Pb, V, and Ni as the major contributors. The other species under study presented moderate risk values. The lifetime cancer risk due only to the exposure to NMVOCs was 170 and 46 times higher than the threshold limit at Zouk and Fiaa, respectively. PM₂.₅-bound PAHs, As, Co, Cr(VI), Ni and V concentrations showed lifetime cancer risk exceeding the threshold limit of 10⁻⁶ with 58 and 28 additional cancer cases per million habitats at Zouk and Fiaa, respectively. To our knowledge, this assessment is a first evaluating the health risk of several classes of compounds from both particulate and gas phases.

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.

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.

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.

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.

Emission characteristics of biogenic volatile organic compounds (BVOCs) (such as isoprene and monoterpenes) emitted from major species of street trees and urban forests by variations in temperature and photosynthetically active radiation (PAR) were investigated. The isoprene and monoterpene emission rates from Prunus sargentii, Ginkgo biloba, Zelkova serrata and Taxus cuspidata were meager. In contrast, the isoprene and monoterpene emission rates from Metasequoia glyptostroboides were very high. In particular, the emission of α-pinene from Metasequoia glyptostroboides was over 10,000 times higher than that from Ginkgo biloba. The patterns of isoprene emissions from the four tree species except for Metasequoia glyptostroboides concerning temperature and PAR were difficult to determine because the emission rate is very low. However, monoterpene emissions from all five tree species were clearly affected by temperature and PAR. These results showed that the characteristics of isoprene and monoterpene emissions differed depending on the tree species. Regarding monoterpene composition, α-pinene (81.3%) accounts for the majority of total monoterpenes from Metasequoia glyptostroboides. This could be a critical consideration when planting trees in an urban forest because BVOC emissions (e.g., α-pinene) have been well known to affect ground-level ozone formation rate via photochemical reaction with NOX. Since Metasequoia glyptostroboides showed relatively high BVOC emissions, the use of this type of tree in an urban forest with relatively high nitrogen oxide emissions should be carefully considered.

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.

Air pollutants influence the morphological, physiological, and biochemical status of plants, and their impacts vary substantially among different species and cultivars. Current review synthesises published literature on the assessment of air pollution impacts on vegetation, with a specific focus on chronicling and summarizing scientific methods that quantify those impacts. Investigations carried out globally on pollutant-plant exposure-response, and articles that describe impact of air pollutants on plants and pollutant abatement using green infrastructure (GI) were systematically reviewed. 273 articles reviewed indicated that a substantial number of past explorations were on a small spectrum of certain species, mainly wheat, rice, soybean and maize; and fewer on non-crop plant species, which cover most of the urban areas and are part of GI. Furthermore, in lower middle-income countries which face significant pollution loads, even studies on crop species are limited. Most studies either use Air Pollution Tolerance Index, which is not pollutant dependent or concentrate on either Ozone or Particulate Matter (PM) and rarely investigate the impact of multiple pollutants in the atmosphere. Also, very few studies differentiate the effect of PM on plants based on its composition. Subsequently, the best possible experimental set ups and wide array of plant health parameters for determining and understanding the effects of different air pollutants on a variety of plant species has been emphasized. While this review compiled literature-based commendations for academic federations wanting to study and quantify air pollutant impacts on vegetation, numerous pertinent vital topics for future research were identified.

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).