Suburban Site Research Articles

Systematic Literature Review on Ozone Dispersion Correlated with Diurnal Concentration Pattern in Urban and Rural Areas


 
 
 Ground level ozone is known to exhibit a strong daily variation of concentration leading to long-range transport of air pollutants from urban to rural areas. Moreover, the characteristics of O3 relationship between urban, suburban, and rural sites can be explained by O3 photochemical chemistry and meteorological dispersions as indicated by the different result of O3 diurnal pattern. However, little is known about the global phenomenon of diurnal concentration of ozone, meteorological dispersion such as long-range transport, and their correlation with ozone precursors, especially in urban and rural areas. This paper attempt to compare the difference between daily ozone fluctuations in both sites and assess some factors that cause long-range ozone transport from urban and rural areas both in subtropical and tropical areas for global scale. Using systematic literature review analysis with the PRISMA method, it examined 43 peer-reviewed articles published between 2010 and 2022 globally meeting the inclusion criteria. The result showed that the fluctuation patterns of daytime ozone in urban and rural areas are different to those in tropical and subtropical regions, depending on latitude. This was primarily due to the influence of solar radiation and the presence of precursors. Conversely, a slight decrease in ozone rate at night occurs because the precursor was accumulated by the shutdown of photochemical ozone production. Some precursors of ozone from other regions can be transported and accumulated from the long-range transport process in other locations. This paper serves as an initial guideline to analysing the pattern of ozone concentration in urban and rural areas and the factors that influence it.
 
 

Systematic Literature Review on Ozone Dispersion Correlated with Diurnal Concentration Pattern in Urban and Rural Areas


 
 
 Ground level ozone is known to exhibit a strong daily variation of concentration leading to long-range transport of air pollutants from urban to rural areas. Moreover, the characteristics of O3 relationship between urban, suburban, and rural sites can be explained by O3 photochemical chemistry and meteorological dispersions as indicated by the different result of O3 diurnal pattern. However, little is known about the global phenomenon of diurnal concentration of ozone, meteorological dispersion such as long-range transport, and their correlation with ozone precursors, especially in urban and rural areas. This paper attempt to compare the difference between daily ozone fluctuations in both sites and assess some factors that cause long-range ozone transport from urban and rural areas both in subtropical and tropical areas for global scale. Using systematic literature review analysis with the PRISMA method, it examined 43 peer-reviewed articles published between 2010 and 2022 globally meeting the inclusion criteria. The result showed that the fluctuation patterns of daytime ozone in urban and rural areas are different to those in tropical and subtropical regions, depending on latitude. This was primarily due to the influence of solar radiation and the presence of precursors. Conversely, a slight decrease in ozone rate at night occurs because the precursor was accumulated by the shutdown of photochemical ozone production. Some precursors of ozone from other regions can be transported and accumulated from the long-range transport process in other locations. This paper serves as an initial guideline to analysing the pattern of ozone concentration in urban and rural areas and the factors that influence it.
 
 

Field observations of C2 and C3 organosulfates and insights into their formation mechanisms at a suburban site in Hong Kong

Organosulfates (OSs) are formed from volatile organic compounds (VOCs) and their oxidation products in the presence of sulfate particles. While OSs represent an important component in secondary organic aerosol, the knowledge of their formation driving force, mechanisms, and environmental impact remain inadequately understood. In this study, we report ambient observations of C2–3 oxygenated VOCs derived OSs (C2–3 OSs) at a suburban location of Hong Kong during autumn 2016. The C2–3 OSs, including glycolaldehyde sulfate (GS), hydroxyacetone sulfate (HAS), glycolic acid sulfate (GAS), and lactic acid sulfate (LAS), were quantified/semi-quantified using offline liquid chromatography-mass spectrometry analysis of aerosol filter samples. The average sum concentration of C2–3 OSs was 36 ng/m3. Correlation analysis revealed that sulfate, surface area, and liquid water content were important factors influencing C2–3 OS formation. Online measurement with an iodide High-Resolution Time-of-Flight Chemical-Ionization Mass Spectrometer (HR-ToF-CIMS) coupled with the Filter Inlet for Gases and AEROsols (FIGAERO) was also conducted to monitor C2–3 OSs, and their potential oxygenated VOC precursors in both gas- and particle-phase, and aerosol acidity tracer simultaneously. Our measurements support that glycolaldehyde/glyoxal, hydroxyacetone, glycolic acid/glyoxal, and lactic acid/methylglyoxal are likely precursors for GS, HAS, GAS, and LAS, respectively. Additionally, we found strong correlation between C2–3 OSs and H3S2O8−, a marker for aerosol acidity, providing field observational evidence for acid-catalyzed formation of small OSs. Based on both online and offline measurements, acid-catalyzed formation mechanisms in particle/aqueous phase are proposed. Specifically, the unique structure of adjacent carbonyl and hydroxyl groups in the C2–3 oxygenated VOC precursors can facilitate the formation of (1) a five-member ring intermediate via intramolecular hydrogen bond to react with sulfur trioxide through heterogenous reaction or (2) cyclic sulfate intermediate via particle-phase reaction with sulfuric acid to generate C2–3 OSs. These proposed mechanisms provide an alternative pathway for the liquid-phase production of C2–3 OSs.

Degree of urbanization and vegetation type shape soil biodiversity in city parks

Urbanization negatively impacts aboveground biodiversity, such as bird and insect communities. City parks can reduce these negative impacts by providing important habitat. However, it remains poorly understood how the degree of urbanization and vegetation types within city parks (e.g., lawns, woodland) impact soil biodiversity. Here we investigated the impact of the degree of urbanization (urban vs. suburban) and vegetation type (lawn, shrub-lawn, tree-lawn and tree-shrub mixtures) on soil biodiversity in parkland systems. We used eDNA metabarcoding to characterize soil biodiversity of bacteria, fungi, protists, nematodes, meso- and macrofauna across park vegetation types in urban and suburban regions in Xiamen, China. We observed a strong effect of the degree of urbanization on the richness of different soil biota groups, with higher species richness of protists and meso/macrofauna in urban compared to suburban areas, while the richness of bacteria and fungi did not differ, and the difference of nematode richness depended on vegetation type. At the functional level, increased degree of urbanization associated with greater species richness of bacterivores, plant pathogens and animal parasites. These urbanization effects were at least partly modulated by higher soil phosphorous levels in urban compared to suburban sites. Also, the vegetation type impacted soil biodiversity, particularly fungal richness, with the richness of pathogenic and saprotrophic fungi increasing from lawn to tree-shrub mixtures. Tree-shrub mixtures also had the highest connectedness between biotas and lowest variation in the soil community structure. Overall, we show that soil biodiversity is strongly linked to the degree of urbanization, with overall richness increasing with urbanization, especially in bacterivores, plant pathogens and animal parasites. Targeted management of vegetation types in urban areas should provide a useful way to help mitigate the negative effect of urbanization on soil biodiversity.

Energy efficiency and environmental impacts of horizontal small wind turbines in Austria

Small wind turbines (SWT) can contribute to the urgent need of transforming the energy system. Nevertheless, due to the heterogeneity of SWT technology, a high variety in environmental impacts of SWT exist. To evaluate whether the use of horizontal SWT can efficiently contribute to a renewable energy system, Life Cycle Assessments of two SWT, a commercial Schachner SW5 and a do-it yourself turbine in the Piggot Pig2F design, were conducted. The energy payback time was calculated using performance measurements from a rural and a suburban site in Austria. Results show that SWTs can reduce greenhouse gas emissions of the Austrian electricity production with calculated global warming potentials of 62gCO2eq/kWh (SW5) and 94gCO2eq/kWh (Pig2F) respectively. For both SWTs, the sub-system tower with foundation contributes about half to their overall global warming potential as well as to the cumulative energy demand. An improved shaping of SWT technology is therefore exemplified by both SWTs. The analysis shows that 19 out of 20 considered impact categories can be reduced by using secondary (recycled) or re-used steel, especially for the tower. The rural and suburban use of horizontal SWT can potentially contribute to reduce the environmental impacts of Austrian electricity production. Nevertheless, it becomes evident that a more sustainable shaping of SWT technology is highly recommendable.

Peroxy radical chemistry during ozone photochemical pollution season at a suburban site in the boundary of Jiangsu–Anhui–Shandong–Henan region, China

Ambient peroxy radical (RO2⁎ = HO2 + RO2) concentrations were measured at a suburban site in a major prefecture-level city (Huaibei) in the boundary of Jiangsu–Anhui–Shandong–Henan region, which is the connecting belt of air pollution in the Beijing–Tianjin–Hebei region and the Yangtze River Delta. Measurements were carried out during the period of September to October 2021 to elucidate the formation mechanism of O3 pollution. The observed maximum concentration of peroxy radicals was 73.8 pptv. A zero-dimensional box model (Framework for 0-Dimensional Atmospheric Modeling, F0AM) based on Master Chemical Mechanism (MCM3.3.1) was used to predict radical concentrations for comparison with observations. The model reproduced the daily variation of peroxy radicals well, but discrepancies still appear in the morning hours. As in previous field campaigns, systematic discrepancies between modelled and measured RO2⁎ concentrations are observed in the morning for NO mixing ratios higher than 1 ppbv. Between 6:00 and 9:00 am, the model significantly underpredicts RO2⁎ by a mean factor of 7.2. This underprediction can be explained by a missing RO2⁎ source of 1.2 ppbv h−1 which originated from the photochemical conversion of an alkene-like chemical species. From the model results it shows that the main sources of ROx (= OH + HO2 + RO2) are the photolysis of oxygenated volatile organic compounds (OVOCs, 33 %), O3 and HONO (25 %), and HCHO (24 %). And the major sinks of ROx transitioned from a predominant reaction of radicals with NOx in the morning to a predominant peroxy self- and cross-reaction in the late afternoon. The introduction of an alkene-like species increased RO2 radical concentration and resulted in 14 % increase in net daily integrated ozone production, indicating the possible significance of the mechanism of alkene-like species oxidation to peroxy radicals. This study provides important information for subsequent ozone pollution control policies in Jiangsu–Anhui–Shandong–Henan region.

The Diversity of Small Mammals along a Large River Valley Revealed from Pellets of Tawny Owl Strix aluco.

The Vistula River is one of the largest European semi-natural rivers of high ecological value that functions as an ecological corridor. To assess the structure of small mammal communities along the Vistula River, an analysis of the diet of an opportunistic predator, the tawny owl Strix aluco, was used. A total of 6355 individuals of 19 species were found, including 5 soricomorph species, 12 rodents, 1 carnivore, and 1 bat species. Tawny owls most frequently caught Apodemus agrarius, Clethrionomys glareolus, Apodemus flavicollis, and Microtus arvalis. Rodents dominated small mammal communities (90%), followed by soricomorphs (8%), and the share of Chiroptera was significant (2%). Using Ward's method in cluster analysis, three clusters of sites with similar mammal communities were identified. The cluster that included 17 study sites with the dominance of agriculture habitats was inhabited by diverse mammal communities with a high number of species. In the cluster composed of three suburban forest sites, mammal communities had the lowest diversity, although the high species richness and the highest shares of the forest species (A. flavicollis, C. glareolus, and Nyctalus noctula). Mammal communities in the cluster were composed of three urban sites were dominated by A. agrarius and M. arvalis. The study indicates the high species richness of small mammals in floodplains of the Vistula River and the adjacent areas in central Poland. The floodplain offers suitable habitats for species associated with forests, water bodies, agricultural land, and developed areas. The data collected confirms earlier model predictions about the presence of well-connected local populations of forest mammals along the Vistula River.

Contrasting effects of clean air actions on surface ozone concentrations in different regions over Beijing from May to September 2013–2020

Due to the nonlinear impacts of meteorology and precursors, the response of ozone (O3) trends to emission changes is very complex over different regions in megacity Beijing. Based on long-term in-situ observations at 35 air quality sites (four categories, i.e., urban, traffic, northern suburban and southern suburban sites) and satellite data, spatiotemporal variability of O3, gaseous precursors, and O3-VOCs-NOx sensitivity were explored through multiple metrics during the warm season from 2013 to 2020. Additionally, the contribution of meteorology and emissions to O3 was separated by a machine-learning-based de-weathered method. The annual averaged MDA8 O3 and O3 increased by 3.7 and 2.9 μg/m3/yr, respectively, with the highest at traffic sites and the lowest in northern suburb, and the rate of Ox (O3 + NO2) was 0.2 μg/m3/yr with the highest in southern suburb, although NO2 declined strongly and HCHO decreased slightly. However, the increment of O3 and Ox in the daytime exhibited decreasing trends to some extent. Additionally, NOx abatements weakened O3 loss through less NO titration, which drove narrowing differences in urban-suburban O3 and Ox. Due to larger decrease of NO2 in urban region and HCHO in northern suburb, the extent of VOCs-limited regime fluctuated over Beijing and northern suburb gradually shifted to transition or NOx-limited regime. Compared with the directly observed trends, the increasing rate of de-weathered O3 was lower, which was attributed to favorable meteorological conditions for O3 generation after 2017, especially in June (the most polluted month); whereas the de-weathered Ox declined except in southern suburb. Overall, clean air actions were effective in reducing the atmospheric oxidation capacity in urban and northern suburban regions, weakening local photochemical production over Beijing and suppressing O3 deterioration in northern suburb. Strengthening VOCs control and keeping NOx abatement, especially in June, will be vital to reverse O3 increase trend in Beijing.

Abundant oxygenated volatile organic compounds and their contribution to photochemical pollution in subtropical Hong Kong

Volatile organic compounds (VOCs), which are ubiquitous pollutants in the urban and regional atmosphere, promote the formation of ozone (O3) and secondary organic aerosols, thereby significantly affecting the air quality and human health. The ambient VOCs at a coastal suburban site in Hong Kong were continuously measured using proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) from November 2020 to December 2020. 83 VOC species, including 23 CxHy, 53 CxHyO1-3, and 7 nitrogen-containing species, were measured during the campaign, with a mean concentration of 36.75 ppb. Oxygenated VOCs (OVOCs) accounted for most (77.4%) of the measured species, including CxHyO1 (50.7%) and CxHyO2 (25.1%). The measured VOC species exhibited distinct temporal and diurnal variations. High concentrations of isoprene and OVOCs were measured in autumn with more active photochemistry, whereas large evening peaks of aromatics from local and regional primary emissions were prominent in winter. The OH reactivity and O3 formation potential (OFP) of key precursors were quantified. OVOCs contributed about half of the total OH reactivity and OFP, followed by alkenes and aromatics, and the contribution of aromatics increased significantly in winter. The potential source contribution function was used to investigate the potential source regions associated with high VOC concentrations. Through positive matrix factorization analysis, six major sources were identified based on fingerprint molecules. The contributions of biogenic sources and secondary formation to the observed species were notable in late autumn, whereas vehicle emissions and solid fuel combustion had higher contributions in winter. The findings highlight the important role of OVOCs in photochemical pollution and provide valuable insights for the development of effective pollution control strategies.

The influence of lightning activity on NOx and O3 in the Pearl River Delta region

Extremely high-temperature lightning generates NOx by electrolyzing nitrogen and oxygen molecules, regulating ozone concentration. The Pearl River Delta (PRD) is located in the world's high-value area of lightning density, and lightning-generated NOx (LNOx) cannot be ignored. Using the flash data from Guangdong-Hong Kong-Macao Lightning Location System and multi-site atmospheric composition data, we estimate the NOx variations in lightning activity and its impact on O3 across the PRD region. The cloud-to-groud (CG) frequency from 2013 to 2021 shows a decreasing trend driven by urban regions. We observe that the lightning density is steadily decreasing from the south-central part of Guangzhou City to the surrounding area.A comparison of the different sites with lightning days and non-lightning days shows that a significant amount (13. 84–20. 47 %) of ground-level NOx concentration at urban stations can be attributed to lightning NOx emissions. A lower lightning frequency and low background concentration observed at suburban sites indicated a limited contribution of LNOx. The average decrease in O3 concentration at urban stations (15.92–25.06 %) was significantly higher than that at suburban stations (5.34–8.95 %) due to the influence of titration and lower actinic radiation. There was a greater fluctuation in NOx and O3 concentrations during the cases, and the surface NOx concentration displayed the most significant responsiveness to LNOx under direct lightning striking in the tall tower. This phenomenon has not been reported, however, it is consistent with the laboratory-based observations suggesting the amount of LNO increases with peak current. LNOx significantly impacts air quality in the PRD during the high convective season. Further in situ and vertical distribution observations are necessary to explore the ground-level impact of LNOx.

Ambient Volatile Organic Compound Characterization, Source Apportionment, and Risk Assessment in Three Megacities of China in 2019.

In order to illustrate pollution characterization, source apportionment, and risk assessment of VOCs in Beijing, Baoding, and Shanghai, field observations of CO, NO, NO2, O3, and volatile organic compounds (VOCs) were conducted in 2019. Concentrations of VOCs were the highest in Beijing (105.4 ± 52.1 ppb), followed by Baoding (97.1 ± 47.5 ppb) and Shanghai (91.1 ± 41.3 ppb). Concentrations of VOCs were the highest in winter (120.3 ± 61.5 ppb) among the three seasons tested, followed by summer (98.1 + 50.8 ppb) and autumn (75.5 + 33.4 ppb). Alkenes were the most reactive VOC species in all cities, accounting for 56.0%, 53.7%, and 39.4% of ozone formation potential in Beijing, Baoding, and Shanghai, respectively. Alkenes and aromatics were the reactive species, particularly ethene, propene, 1,3,5-trimethylbenzene, and m/p-xylene. Vehicular exhaust was the principal source in all three cities, accounting for 27.0%, 30.4%, and 23.3% of VOCs in Beijing, Baoding, and Shanghai, respectively. Industrial manufacturing was the second largest source in Baoding (23.6%) and Shanghai (21.3%), and solvent utilization was the second largest source in Beijing (25.1%). The empirical kinetic modeling approach showed that O3 formation was limited by both VOCs and nitric oxides at Fangshan (the suburban site) and by VOCs at Xuhui (the urban site). Acrolein was the only substance with an average hazard quotient greater than 1, indicating significant non-carcinogenic risk. In Beijing, 1,2-dibromoethane had an R-value of 1.1 × 10-4 and posed a definite carcinogenic risk.

Combination of multiple stable isotope and elemental analyses in urban trees reveals air pollution and climate change effects in Central Mongolia

The Ulaanbaatar area in Mongolia has become one of the most polluted regions worldwide due to the rapid increase in urbanization, industrial activity and traffic. However, we critically lack knowledge on the impacts of air pollution on surrounding forest ecosystems that may be further amplified by the ongoing climate change. Here, we apply a novel combination of multiple stable isotope analyses (nitrogen: δ15N, carbon: δ13C, oxygen: δ18O, hydrogen: δ2H) in foliar and tree-ring samples from different tree species, including deciduous, broadleaf species (poplar and birch), a deciduous conifer (larch) and needle evergreen species (spruce and Scots pine). This was complemented by trace element analysis, to study the influence of air pollution and climate on urban, suburban and more remote forests in and around Ulaanbaatar. We found indications of pollution effects in urban and suburban sites in foliar material, particularly in δ15N, with unusually high values of > 10‰, that could be related to tree uptake of NOx. Results were similar for all species, but with a smaller effect for Scots pine. The tree-ring δ15N values were found to be clearly enriched in recent years compared to 50 years ago at the urban sites, consistent with a pollution signal. Leaves and needles at suburban and urban sites had accumulated higher concentrations of various trace elements including Al, B, Ba, Ca, Cr, Cu, Fe, Mg, Na, S and Zn compared to the more distant sites, confirmed by Principal Component Analysis. Our data on δ13C, δ18O and δ2H enabled us to infer possible physiological effects induced by air pollution. Consistently increasing tree-ring δ13C values over recent decades for all investigated species indicated increasing plant stress, like hampered stomatal conductance and photosynthesis, but this was found for all sites, suggesting climate change rather than air pollution effects. In summary, we show that our multi-isotope and -element approach provides new insights into the threats to forests in urban areas, where the occurrence of more frequent droughts acts together with air pollution.

Volatility Parametrization of Low-Volatile Components of Ambient Organic Aerosols Based on Molecular Formulas.

Evaluating the volatility of organic compounds based solely on their molecular formulas would avoid tough demands in deriving molecular structures. Here, we deployed an iodide-adduct Long Time-of-Flight Chemical Ionization Mass Spectrometry (LToF-CIMS) combined with a Filter Inlet for Gases and AEROsols (FIGAERO) to investigate molecular formulas and thermograms of organic compounds on ambient particulate samples collected in the summer of 2021 in a suburban site of Shanghai and to estimate saturation vapor pressures of low- and semivolatile components of ambient organic aerosols. Then, a hierarchical cluster analysis and a subsequent classification of obtained clusters by similarity calculation were applied to the measured data set of molecular formulas and saturation vapor pressures of organic aerosols with at least a 2/3 appearance frequency, together with a similar data set collected at a rural site in the Beijing-Tianjin-Hebei region during the winter of 2018 (Ren et al., 2018), to classify all compounds into multiple groups. For each group of compounds, parametrizations between volatility and elemental composition were derived, and then relationships between each group of parameters and the mean O:C were established to achieve a volatility-molecular formula parametrization with the O:C as a key input. Statistical comparison of estimated volatilities of low-volatile organic compounds shows a much better performance of our parametrization than previous molecular formula-based ones.

Impact of fossil and non-fossil fuel sources on the molecular compositions of water-soluble humic-like substances in PM2.5 at a suburban site of Yangtze River Delta, China

Abstract. Atmospheric humic-like substances (HULIS) affect the global radiation balance due to their strong light absorption at the ultraviolet wavelength. The potential sources and molecular compositions of water-soluble HULIS at a suburban site in the Yangtze River Delta from 2017 to 2018 were discussed, based on the results of the radiocarbon (14C) analysis and combining the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) technique in this study. The 14C results showed that the averaged non-fossil-fuel source contributions to HULIS were 39 ± 8 % and 36 ± 6 % in summer and winter, respectively, indicating significant contributions from fossil fuel sources to HULIS. The Van Krevelen diagrams obtained from the FT-ICR-MS results showed that the proportions of tannin-like and carbohydrate-like groups were higher in summer, suggesting significant contribution of HULIS from biogenic secondary organic aerosols (SOAs). The higher proportions of condensed aromatic structures in winter suggested increasing anthropogenic emissions. Molecular composition analysis on the CHO, CHON, CHOS, and CHONS subgroups showed relatively higher intensities of high O-containing macromolecular oligomers in the CHO compounds in summer, further indicating stronger biogenic SOA formation in summer. High-intensity phenolic substances and flavonoids, which were related to biomass burning and polycyclic aromatic hydrocarbon (PAH) derivatives indicating fossil fuel combustion emissions, were found in winter CHO compounds. Besides, two high-intensity CHO compounds containing condensed aromatic ring structures (C9H6O7 and C10H5O8) identified in the summer and winter samples were similar to those from off-road engine samples, indicating that traffic emissions were one of the important fossil fuel sources of HULIS at the study site. The CHON compounds were mainly composed of nitro compounds or organonitrates with significantly higher intensities in winter, which were associated with biomass burning emissions, in addition to the enhanced formation of organonitrates due to high NOx in winter. However, the high-intensity CHON molecular formulas in summer were referring to N-heterocyclic aromatic compounds, which were produced from the atmospheric secondary processes involving reduced N species (e.g., ammonium). The S-containing compounds were mainly composed of organosulfates (OSs) derived from biogenic precursors, namely long-chain alkane and aromatic hydrocarbon, which illustrate the mixed sources of HULIS. Generally, different policies need to be considered for each season due to the different seasonal sources (i.e., biogenic emissions in summer and biomass burning in winter for non-fossil-fuel sources, traffic emissions and anthropogenic SOA formation in both seasons, and additional coal combustion in winter). Measures to control emissions from motor vehicles and industrial processes need to be considered in summer. Additional control measures on coal power plants and biomass burning should be applied in winter. These findings add to our understanding of the interaction between the sources and the molecular compositions of atmospheric HULIS.

Budget of atmospheric nitrous acid (HONO) during the haze and clean periods in Shanghai: Importance of heterogeneous reactions

Nitrous acid (HONO) plays a significant role in radical cycling and atmospheric oxidative chemistry. While the source and evolution of HONO in the Yangtze River Delta (YRD) region of China after 2018 remains largely unknown, this work monitored HONO and other air pollutants throughout 2019 at an urban site (Pudong, PD) and a suburban site (Qingpu, QP) in Shanghai. Episodes with high HONO mixing ratios but different PM2.5 levels, namely haze and clean episodes, were chosen for HONO budget analysis. Using an observation-based photochemical box model, relative importance of different sources and sinks of HONO were evaluated. Gas-phase reaction of NO with OH was found to be one of the most important daytime HONO formation sources, especially during the QPhaze period (accounting for 40.3 % of daytime HONO formation). In particular, heterogeneous conversion of NO2 on ground and aerosol surface was found to be the dominant source for nocturnal HONO. Photo-enhanced NO2 conversion on ground surface plays an important role in daytime HONO production (19.4 % in PDhaze vs. 27.6 % in PDclean, and 19.8 % in QPhaze vs. 25.9 % in QPclean). In addition, photo-enhanced NO2 conversion at the aerosol surface during haze episodes made more significant contributions to HONO formation compared to the clean periods (20.9 % in PDhaze vs. 17.1 % in PDclean, and 19.7 % in QPhaze vs. 11.2 % in QPclean). The role of multiphase reactions was found to be increasingly important in HONO generation with enhanced relative humidity (RH) during daytime. Significant unknown HONO source was further analyzed and found to be positively related with photolytic as well as multiphase pathways. Overall, our study sheds light on the budget of HONO in one of the biggest megacities in east China, which would help developing future mitigation strategies for urban HONO and atmospheric oxidation capacity.

Significant differences in black and brown carbon concentrations at urban and suburban sites

Light-absorbing carbonaceous particles (LAC) may cause and/or exacerbate non-communicable diseases, interfere with the Earth's radiative balance, darken urban buildings and impair vistas. In this study, we explored the temporal behaviour of LAC concentrations measured at wavelengths of 370 nm (brown carbon, BrC) and 880 nm (black carbon, BC) at two sites of a mid-sized city in Brazil. We observed sharp changes in LAC concentrations at the city centre site in response to variations in traffic volume. The highest concentrations were observed when winds originated from both the city core and from the direction of the bus terminal. The suburban site exhibited a notably uniform diurnal pattern and consistently lower LAC concentrations throughout the day. Nevertheless, substantial increases during the evening led to mean BrC and BC concentrations (2.6 and 2.2 μg m−3, respectively) comparable to daytime peaks observed in the city centre (3 μg m−3 and 2.5 μg m−3). This phenomenon was attributed to the burning of residential waste and overgrown vegetation in nearby vacant lots. Moreover, the highest concentrations coincided with periods of low wind speeds, usually linked to non-buoyant plumes from point sources. BrC concentrations surpassed BC concentrations, even at the city centre site. Not only was the Ångström absorption exponent (Å370/880) larger at the suburban site compared to the city centre (95th percentiles of 1.73 and 1.38, respectively), but it also exhibited a wider span. Overall, the combined LAC and Å370/880 data indicated that i) biomass burning is a major source of LAC at the suburban site; ii) at the city centre, bare BC particles may become internally mixed with BrC from biomass or fossil fuel emissions and enhance absorption at lower wavelengths. The occurrence of LAC peaks outside the evening rush hours suggests that other sources but on-road vehicular emissions may contribute to the deterioration of the air quality in the urban core. Tackling air quality across the urban perimeter requires targeting other potential sources but traffic emissions.

Concurrent measurements of nitrate at urban and suburban sites identify local nitrate formation as a driver for urban episodic PM2.5 pollution

Nitrate (NO3−) is often among the leading components of urban particulate matter (PM) during PM pollution episodes. However, the factors controlling its prevalence remain inadequately understood. In this work, we analyzed concurrent hourly monitoring data of NO3− in PM2.5 at a pair of urban and suburban locations (28 km apart) in Hong Kong for a period of two months. The concentration gradient in PM2.5 NO3− was 3.0 ± 2.9 (urban) vs. 1.3 ± 0.9 μg m−3 (suburban) while that for its precursors nitrogen oxides (NOx) was 38.1 vs 4.1 ppb. NO3− accounted for 45 % of the difference in PM2.5 between the sites. Both sites were characterized to have more available NH3 than HNO3. Urban nitrate episodes, defined as periods of urban-suburban NO3− difference exceeding 2 μg m−3, constituted 21 % of the total measurement hours, with an hourly NO3− average gradient of 4.2 and a peak value of 23.6 μg m−3. Our comparative analysis, together with 3-D air quality model simulations, indicates that the high NOx levels largely explain the excessive NO3− concentrations in our urban site, with the gas phase HNO3 formation reaction contributing significantly during the daytime and the N2O5 hydrolysis pathway playing a prominent role during nighttime. This study presents a first quantitative analysis that unambiguously shows local formation of NO3− in urban environments as a driver for urban episodic PM2.5 pollution, suggesting effective benefits of lowering urban NOx.

The variability of mass concentrations and source apportionment analysis of equivalent black carbon across urban Europe

This study analyzed the variability of equivalent black carbon (eBC) mass concentrations and their sources in urban Europe to provide insights into the use of eBC as an advanced air quality (AQ) parameter for AQ standards. This study compiled eBC mass concentration datasets covering the period between 2006 and 2022 from 50 measurement stations, including 23 urban background (UB), 18 traffic (TR), 7 suburban (SUB), and 2 regional background (RB) sites. The results highlighted the need for the harmonization of eBC measurements to allow for direct comparisons between eBC mass concentrations measured across urban Europe. The eBC mass concentrations exhibited a decreasing trend as follows: TR > UB > SUB > RB. Furthermore, a clear decreasing trend in eBC concentrations was observed in the UB sites moving from Southern to Northern Europe. The eBC mass concentrations exhibited significant spatiotemporal heterogeneity, including marked differences in eBC mass concentration and variable contributions of pollution sources to bulk eBC between different cities. Seasonal patterns in eBC concentrations were also evident, with higher winter concentrations observed in a large proportion of cities, especially at UB and SUB sites. The contribution of eBC from fossil fuel combustion, mostly traffic (eBCT) was higher than that of residential and commercial sources (eBCRC) in all European sites studied. Nevertheless, eBCRC still had a substantial contribution to total eBC mass concentrations at a majority of the sites. eBC trend analysis revealed decreasing trends for eBCT over the last decade, while eBCRC remained relatively constant or even increased slightly in some cities.

Socioeconomic Disparities in Patients Receiving Intravitreal Injections for Age-Related Macular Degeneration Amid the COVID-19 Pandemic.

Purpose: To determine the effects of socioeconomic factors on visit adherence and the resultant visual outcomes for patients receiving intravitreal injections for neovascular age-related macular degeneration during the COVID-19 pandemic. Methods: In this retrospective case-control study, medical records were reviewed to collect appointment attendance, age, sex, self-reported race/ethnicity, primary language, marital status, insurance, distance from clinic, and Area Deprivation Index (ADI), a measure of socioeconomic disadvantage. Multivariate regression models were created to determine differences in socioeconomic factors between individuals who attended (show group) and those who did not attend (no-show group) appointments. Results: The study enrolled 126 patients in the show group and 115 in the no-show group. On univariate analysis, nonadherence was significantly higher in non-White patients than in White patients (P = .04), urban sites than in suburban sites (P = 1.7 × 10-4), and non-English-speaking patients than in English-speaking patients (P = 4.0 × 10-3). The associations remained significant in multivariate analysis for non-English-speaking patients (P = .03) and urban-site patients (P = .01) after adjusting for age, sex, self-reported race/ethnicity, primary language, marital status, insurance, distance from clinic, site of visit, and ADI. At 6 months and 1 year, a 1-, 2-, and 3-line vision loss was significantly higher in the no-show group than in the show group on univariate and multivariate analysis after adjusting for age, sex, race, lens status, and presence of glaucoma and diabetic retinopathy. Conclusions: Non-English-speaking patients and urban-based patients were less likely to present for intravitreal injection appointments during the initial peak of the COVID-19 pandemic. This disparity translated to worse vision outcomes at 6 months and 1 year.

Biogenic volatile organic compounds enhance ozone production and complicate control efforts: Insights from long-term observations in Hong Kong

Ground-level ozone (O3) pollution is a major air-quality issue in China. With decreasing emissions of anthropogenic precursors, natural precursors may become increasingly important in O3 pollution. However, understanding of the change in biogenic volatile organic compounds (BVOCs) and its environmental impact in China has been hindered by the lack of long-term measurements of VOCs. In this study, we analyze the continuous measurements of O3 and its precursors obtained in Hong Kong during 2013–2019 and demonstrate the increasingly important role of BVOCs in O3 production. Driven by the warming temperature, Biogenic isoprene at a suburban site (Tung Chung) increased by 0.05 ± 0.02 ppbv/yr (18%/yr), which is in sharp contrast to the decreases in anthropogenic precursors during the study period. Detailed chemical modeling shows that increased BVOCs enhanced local O3 production by 0.31 ppbv/h/yr (23%) annually, and the effect was the most obvious in summer (by 0.44 ppbv/h/yr or 27%). Increased BVOCs also affected the O3-precursor (anthropogenic) relationships by increasing the O3 sensitivity to nitrogen oxides (NOx) and decreasing the O3 sensitivity to anthropogenic VOCs (AVOCs). Despite changes in precursors (decreasing NOx, increasing BVOCs, and decreasing some AVOCs), the O3 formation remains in VOC-limited regimes at Tung Chung. Joint control of AVOCs and NOx (at a ratio greater than 1.2) would help avoid exacerbation of O3 pollution and reduce NO2 pollution. In the short term, an AVOCs-focused strategy would help reduce O3 to a moderate level; but because of the presence of the natural BVOCs, a drastic cut in NOx emissions would be needed to meet a more stringent O3 standard. Our findings also suggest the BVOCs increase likely occurred in the larger Pearl River Delta (PRD) region, and thus the results from our study in Hong Kong may have implications for developing AVOCs/NOx reduction measures in the PRD region and beyond.