Morning Rush Research Articles

Humidity-Dependent Phase State of Gasoline Vehicle Emission-Related Aerosols.

The phase states of primarily emitted and secondarily formed aerosols from gasoline vehicle exhausts were investigated by quantifying the particle rebound fraction (f). The rebound behaviors of gasoline vehicle emission-related aerosols varied with engines, fuel types, and photochemical aging time, showing distinguished differences from biogenic secondary organic aerosols. The nonliquid-to-liquid phase transition of primary aerosols emitted from port fuel injection (PFI) and gasoline direct injection (GDI) vehicles started at a relative humidity (RH) = 50 and 60%, and liquefaction was accomplished at 60 and 70%, respectively. The RH at which f declined to 0.5 decreased from 70 to 65% for the PFI case with 92# fuel, corresponding to the photochemical aging time from 0.37 to 4.62 days. For the GDI case, such RH enhanced from 60 to 65%. Our results can be used to imply the phase state of traffic-related aerosols and further understand their roles in urban atmospheric chemistry. Taking Beijing, China, as an example, traffic-related aerosols were mainly nonliquid during winter with the majority ambient RH below 50%, whereas they were mostly liquid during the morning rush hour of summer, and traffic-related secondary aerosols fluctuated between nonliquid and liquid during the daytime and tended to be liquid at night with increased ambient RH.

Potential and cumulative accessibility of workplaces by public transport in Szczecin

Abstract The article presents the accessibility of workplaces in Szczecin using the method of potential and cumulative accessibility for commuting by public transport. The public transport commuting times used in the study were generated using the public transport model, which was developed based on data in the General Transit Feed Specification (GTFS) format. The results of potential accessibility by public transport were calculated for several selected time thresholds in the morning rush hours between 7 a.m. and 9 a.m.. On the other hand, cumulative accessibility is characterised by variability of travel times for 8 a.m., which is calculated in 10- to 60-minute intervals of travel time. The aim of this study is to identify workplaces in Szczecin that are situated in areas where accessibility is more dependent on the parameters of the public-transport timetable. In addition, a possibility to define the optimal journey length was assumed so that it would regard the largest number of jobs. The use of the two indicated research methods for the accessibility of workplaces in Szczecin provides a result in the form of better- and less-accessible areas of the city as regards the labour market. The results regarding the accessibility of workplaces using the two methods identify places of increased demand for commuting by public transport during the morning rush hours.

Universal scaling laws of collective human flow patterns in urban regions

Detail observation of human locations became available recently by the development of information technology such as mobile phones with GPS (Global Positioning System). We analyzed temporal changes of global human flow patterns in urban regions based on mobile phones’ GPS data in 9 large cities in Japan. By applying a new concept of drainage basins in analogous to river flow patterns, we discovered several universal scaling relations. These include, the number of moving people in a drainage basin of diameter L is proportional to L^3 in the morning rush hour, which is surprisingly different from reasonable intuition of proportionality to the 2 dimensional area, L^2. We show that this unexpected 3 dimensional feature is related to the strong attraction of the city center to become a 3 dimensional structure due skyscrapers.

КІЛЬКІСНА ОЦІНКА ВПЛИВУ ОБЛАШТУВАННЯ ПАРКУВАЛЬНИХ МІСЦЬ У КРАЙНІЙ ПРАВІЙ СМУЗІ НА ЕФЕКТИВНІСТЬ ДОРОЖНЬОГО РУХУ

Стрімкі темпи росту автомобілізації призвели до значного перевищення попиту на місця паркування над наданою їх кількістю. Подібна ситуація є характерною рисою більшості середніх та великих міст України. В умовах недоліку місць для паркування найбільшого поширення набуло облаштування паркувальних місць у крайній правій смузі. Застосування даного заходу призводить до зниження пропускної спроможності вулично-дорожньої мережі міста та погіршення умов безпеки руху транспорту. Тому, у роботі проаналізовано вплив облаштування таких паркувальних місць на ефективність руху у м. Дніпро. В якості об’єкта дослідження обрано перехрестя вул. Я. Мудрого та вул. Воскресєнської. Інтенсивності транспортних потоків на перехресті були отримані методом натурних обстежень для ранкової години «пік» з 700 до 800. У програмному середовищі PTV VISSIM розроблено дві імітаційні транспортні моделі перехрестя (без смуги та зі смугою для паркування). Результати моделювання, засвідчують, що облаштування паркувальних місць у крайній правій смузі знижує ефективності руху за всіма обраними показниками в діапазоні від 26% до 62%. Значення запропонованого авторами комплексного показника ефективності для дороги без «парковки» становить – 1,00, а для дороги з облаштованою паркувальною зоною – 0,54. Доведено, що загальна ефективність такого рішення для обраного об’єкту дослідження знизила ефективність організації дорожнього руху на 46%. Проведено експертне оцінювання, за результатами якого були розраховані вагові коефіцієнти для обраних показників. Отриманий розподіл вагових коефіцієнтів характеризується дуже незначною розбіжністю. Це засвідчує, що всі обрані авторами показники є значимими під час прийняття остаточних рішень щодо обґрунтування заходів з підвищення ефективності дорожнього руху.

Research on the coupling degree of regional taxi demand and social development from the perspective of job–housing travels

Due to the urban industrial transformation and upgrading in China, the relationship between residential and employment spaces in large cities has changed significantly, resulting in an increasingly prominent job–housing separation phenomenon. Based on the taxi GPS trajectory data, this paper firstly analyzes the time and space distribution of job–housing–travel and the commuting characteristics of residents. Then, we construct the evaluation index systems of regional jobs–housing–taxi demand and regional social development level for Beijing. After calculating the weight of each index by using an entropy weight method, we analyze the coupling relationship between regional taxi demand and social development by building the coupling coordination degree model (CCDM). Conclusions are as follows: Firstly, it shows imbalance of space distribution of taxi orders in different administrative and functional areas. The order quantity gradually decreases from the main urban area to the edge, with the most in the living area, accounting for 46.23% of the total orders. Secondly, the daily variation trend of taxi orders in different functional areas is significantly different. During the morning rush hour, taxi orders flow out of residential areas and into office areas; however, during the evening rush hour, they flow out of the office and into the living area. For example, the residence area has a higher proportion of getting on passengers during the morning rush hour, which is 1.46 times that of the getting off ones. Thirdly, a low coupling coordination degree is observed between the regional social development level and the job–housing–taxi demand in Beijing, with a gradually decreasing from the main urban area to the outside, which is mainly caused by the imbalance between supply and demand. Therefore, it is suggested that the relevant government departments should formulate specific control schemes to traffic congestion according to local commuting features, and promote job–housing balance. Meanwhile, the taxi resources are supposed to be allocated reasonably by the striving to information symmetry, to promote the coordination and sustainability between the regional job–housing–taxi demand and social development level.

Associations of co-exposures to air pollution and noise with psychological stress in space and time: A case study in Beijing, China

Air pollution and noise are both ubiquitous environmental stressors that pose great threats to public health. Emerging evidence has noticed the combined health risks caused by the coexistence of traffic-related air pollutants and noise in the residential context. However, less is known about how mobile individuals are simultaneously exposed to multiple sources of air pollution and noise, and thus respond with more acute psychological responses beyond the residence. This study examines the co-exposures to fine particles (PM2.5) and noise across spatiotemporal contexts where the concurrent exposures are jointly associated with momentary psychological stress. An innovative research protocol, including GPS-equipped activity-travel diaries, air pollutant and noise sensors, and ecological momentary assessment, was adopted to collect real-time data from a sample of residents in Beijing, China. The results showed a minor correlation between PM2.5 and noise exposures after accounting for individual mobility and the spatiotemporal dynamics of these two environmental pollutants. Further, exposure to PM2.5 was more associated with momentary psychological stress given the insignificant independent effect and the weak moderating effect of noise exposure. Three specific spatiotemporal contexts involving the health risks of co-exposures were delineated, including morning rush hours and traveling by public transits with intensified stress risks caused by combined exposures to air pollution and noise, workplaces with counteracting stress effect of both exposures, and evening time at home with stress-induced air pollution and stress-relieving social noise. In conclusion, the mobility-based and context-aware analysis provides a more nuanced understanding of the associations of co-exposures to environmental pollution and synchronous psychological stress in space and time.

Characterizing start emissions of gasoline vehicles and the seasonal, diurnal and spatial variabilities in China

Start emissions from gasoline light-duty passenger vehicles (LDPVs) remain an important source of emissions modeling. This study measured start emissions of gaseous pollutants and solid particle number based on dynamometer tests for a fleet of 111 LDPVs in China, and selected a portion of samples to be tested under low temperature or shorter soak conditions. The cold-start phase, defined to follow soak durations of more than 6 h, typically lasts less than 200 s but accounts for a high proportion of total tailpipe emissions under the regulatory cycle (e.g., ~60% for China 6 CO emissions). Low temperature predominantly increases start emissions rather than hot-running emissions, and the increase ratios vary by pollutant and vehicle technology. Metrological data and soak duration profiles informed by a large sample of LDPVs were used to quantify the seasonal, diurnal and spatial variabilities of LDPV emissions across China. One notable case indicates that tailpipe THC emissions in January could be 283% higher than those in July for the fleet in Beijing, and the emissions peak in the morning rush hour during a day due to long overnight soak durations. This study provides a comprehensive dataset and useful tools for addressing the seasonal, diurnal and spatial variations in tailpipe emissions of gasoline vehicles in China, and has the potential to improve future emission inventories and air quality simulations.

Impact of traffic origin particulate matter and its chemical constituents on oxidative potential

Currently high particulate matter (PM) levels are observed in most of the urban cities of India and one of the major sources of emissions are vehicle plying on roads. Exposure to PM and its components have been linked with various disorders and has been associated with the ability to produce free radicals and reactive oxygen species, known as “oxidative potential” of PM and is proposed to be one of the most relevant indicators of PM toxicity. In the present study we examined the oxidative potential of PM collected at roadside (RS) and urban background (BG) site using dithiothreitol (DTT) assay. PM measurements were carried out simultaneously at both the sites in Mumbai on seven consecutive days, covering both morning (7:00-11:00 AM) and afternoon (12:00-4:00 PM) hours in May 2018 using low volume sampler (Mini vol, Airmetrics, USA flow rate of 5 l min-1). The collected samples was analysed for carbonaceous aerosols (OC, EC, and WSOC) and trace elemental components of PM. The average mass concentration at RS and BG during morning rush hours was 80±23 µgm-3 and 43±10 µgm-3 while in the afternoon it was 84±14.8 µgm-3 and 53±13 µgm-3, respectively. The average OC, EC levels at RS were 19.8±8.8 µgm-3, 16.5±5.1 µgm-3 (morning), 21.8±9.4, 19.1±13.5 µgm-3 (afternoon), whereas at BG site it was 16.5±9.9 µgm-3, 2.5±2.1 µgm-3 (morning), 16±13 µgm-3, 3.5±3.4 µgm-3 (afternoon) respectively. The corresponding WSOC levels at RS and BG were 11% and 19% during morning period while during afternoon it was 15% and 27% of OC, respectively. The volume normalised DTT activity (DTTv) was higher at the roadside (1.12±0.54 nmol min-1 m-3) during morning period than at background (0.75±0.6 nmol min-1 m-3). Thus, our first results suggest that exposure to PM from traffic related emissions may pose substantial risk to a large population in urban areas.

An activity-based bottleneck model with stochastic capacity

This study investigated commuters’ departure time choice with stochastic capacity. It has typically been solved by using Vickrey’s bottleneck model which doesn’t take the impact of commuters’ activity on decision-making into account. We added activity utility parameters to Vickrey’s bottleneck model. Travel costs became negative utility. The model considered home-activity utility before work and work-activity utility in the morning rush. Simultaneously, the capacity of the bottleneck changed randomly between a designed value (good condition) and a degraded one(bad condition). We derived six reasonable equilibrium patterns by maximizing the commuters’ activity utility and closed form solutions to all possible equilibrium patterns. The departure rate curve for each equilibrium pattern was made within a reasonable parameter range.

Оценка динамики загрязнения атмосферного воздуха городского центра выбросами автомобильного транспорта картографическим методом

When characterizing vehicle emissions, as a rule, the speed of traffic flows is not taken into account, which significantly reduces its accuracy. In this regard, the use of the cartographic method for assessing the speed of traffic flows on the tracks is quite reasonable and relevant. The assessment of the intra-annual dynamics of the intensity of traffic flows and emissions of the main components of exhaust gases by vehicles on the streets of the city of Ryazan and bypass roads using a cartographic method for recording the intensity of traffic flows was carried out. The study was conducted in 2018–2019 on the territory of Ryazan. The material used for the study was cartographic data published in free access on the website www.yandex.ru traffic jams. The length of traffic flows with a speed of 5-10 km / h (heavy traffic conditions – TTU) was determined at different times of the day on days of the week. The indicators of the average hourly length of heavy transport conditions were calculated. Bypass roads of the city were characterized by a significantly greater length of sections with TTU compared to the city streets from Tuesday to Thursday and Sunday (p<0.05). The increased complication of traffic conditions during morning and evening rush hours led to an average annual increase in emissions of the main components of vehicle exhaust gases of 17.7% and 14.9% respectively, with the largest increase in emissions being typical for the city center. At the same time, the maximum complication of transport conditions on the bypass roads was observed in the summer and spring (from Monday to Wednesday and Sunday), while on city highways - on working days in the autumn and weekends in winter. On the city streets, the greatest length of heavy traffic conditions during the morning rush hour was observed in winter, and the shortest was in summer, while the evening rush hour, on the contrary, was most pronounced in autumn. On the bypass roads, there was a clear tendency towards heavier transport conditions over a longer period of the day according to the scheme winter–autumn–spring– summer.

Assessing 3-D Spatial Extent of Near-Road Air Pollution around a Signalized Intersection Using Drone Monitoring and WRF-CFD Modeling.

In this study, we have assessed the three-dimensional (3-D) spatial extent of near-road air pollution around a signalized intersection in a densely populated area using collaborating methodologies of stationary measurements, drone monitoring, and atmospheric dispersion modeling. Stationary measurement data collected in the roadside apartment building showed a substantial effect of emitted pollutants, such as nitrogen oxides (NOx), black carbon (BC), and ultrafine particles (UFPs), especially during the morning rush hours. Vertical drone monitoring near the road intersection exhibited a steeper decreasing trend with increasing altitude for BC concentration rather than for fine particulate matter (PM2.5) concentration below the apartment building height. Atmospheric NOx dispersion was simulated using the weather research and forecasting (WRF) and computational fluid dynamics (CFD) models for the drone measurement periods. Based on the agreement between the measured BC and simulated NOx concentrations, we concluded that the air pollution around the road intersection has adverse effects on the health of residents living within the 3-D spatial extent within at least 120 m horizontally and a half of building height vertically during the morning rush hours. The comparability between drone monitoring and WRF-CFD modeling can further guarantee the identification of air pollution hotspots using the methods.

What the COVID-19 lockdown revealed about photochemistry and ozone production in Quito, Ecuador

The COVID-19 lockdown presented a peculiar opportunity to study a shift in the photochemical regime of ozone production in Quito (Ecuador) before and after mobility restrictions. Primary precursors such as NO and CO dropped dramatically as early as 13 March 2020, due to school closures, but ambient ozone did not change. In this work we use a chemical box model in order to estimate regimes of ozone production before and after the lockdown. We constrain the model with observations in Quito (ozone, NOx, CO, and meteorology) and with estimations of traffic-associated VOCs that are tightly linked to CO. To this end, we use the closest observational data of VOC/CO ratios at an urban area that shares with Quito conditions of high altitude and is located in the tropics, namely Mexico City. A shift in the chemical regime after mobility restrictions was evaluated in light of the magnitude of radical losses to nitric acid and to hydrogen peroxide. With reduced NOx in the morning rush hour (lockdown conditions), ozone production rates at 08:30–10:30 increased from 4.2–17 to 9.7–23 ppbv h−1, respectively. To test further the observed shift in chemical regime, ozone production was recalculated with post-lockdown NOx levels, but setting VOCs to pre-lockdown conditions. This change tripled ozone production rates in the mid-morning and stayed higher throughout the day. In light of these findings, practical scenarios that present the potential for ozone accumulation in the ambient air are discussed.

Diurnal and seasonal variations in water-soluble inorganic ions and nitrate dual isotopes of PM2.5: Implications for source apportionment and formation processes of urban aerosol nitrate

Recently, increasing urban aerosol NO3− deposition have aroused widespread attention. To reveal its sources and formation processes, the water-soluble inorganic ions (WSIIs) and NO3− dual isotopes (i.e., δ15N and δ18O) were measured in fine particles (i.e., PM2.5), which were collected during rush hours in the morning and afternoon, and non-rush hours at noon, discretely in winter and in summer at urban Guiyang, southwest China. Results showed the sulfate, nitrate, and ammonium together accounted for more than 90% of the total WSIIs in both seasons. Both NO3− and its dual isotopes were distinctly higher in winter than in summer. While only NO3− and δ15N were observed significantly higher during rush hours than the non-rush hours in summer, which could be potentially controlled by the temperature, relative humidity and ambient NH3 contents. The gradual but insignificant increase of δ18O during from morning to afternoon were ascribed to the decreasing contributions of •OH oxidation pathway. By using the Bayesian isotope mixing model, we revealed the coal combustion and biomass burning accounted for the predominant NOx sources in contributing to the particulate NO3− in winter, followed by vehicular and soil biogenic emissions. Whereas in summer, biomass burning played the most important role, since the coal combustion proportion sharply decreased. Moreover, the particle NO3− source contributions showed minor difference during diurnal periods in winter, while the difference was larger in summer, especially for that during between morning rush and noon non-rush hours, which were likely due to the changes of NOx emissions (e.g. from vehicular and soil biogenic source), as well as the meteorological conditions.

Estimated contribution of vehicular emissions to carbonaceous aerosols in urban Beijing, China

Worldwide attention has been focused on air pollution associated with vehicle emissions. With the highest number of vehicles, Beijing has experienced air pollution related to vehicle emissions. To better recognize the contributions of vehicle emissions to organic carbon (OC) and elemental carbon (EC), hourly measurements of OC and EC in PM2.5 were conducted in urban Beijing from June 1, 2016 to May 31, 2017 in addition to auxiliary measurements of water-soluble ions and elements. The average concentrations of OC and EC were 11.9 ± 11.1 and 3.7 ± 3.6 μg/m3 during the study period, respectively, while those of OC and EC during the nighttime (0:00–6:00), morning rush hour (7:00–9:00) and evening rush hour (17:00–19:00) were 12.9 ± 12.9 μg/m3 and 4.4 ± 4.3 μg/m3, 10.4 ± 9.8 μg/m3 and 3.7 ± 3.1 μg/m3, and 12.3 ± 8.7 μg/m3 and 3.5 ± 2.4 μg/m3, respectively. The diurnal variations in OC and EC concentrations showed higher values during the nighttime, morning rush hour and evening rush hour. Strong correlations were found between OC and CO (r2 = 0.76–0.79) and between OC and NOx (r2 = 0.63–0.68); strong correlations were also found between EC and CO (r2 = 0.76–0.81) and between EC and NOx (r2 = 0.63–0.68) during the nighttime, morning rush hour and evening rush hour. The results of source apportionment based on the hourly PM2.5-associated chemical composition by a positive matrix factorization model showed that vehicle emissions accounted for 23.0% of PM2.5. From the profiles of the source apportionment of PM2.5, it could be found that vehicle emissions contributed 51.2%, 51.3% and 25.2% of the concentrations of OC, EC and PM2.5 on average during the nighttime, respectively. The contributions of vehicle emissions to OC, EC and PM2.5 during the nighttime were higher than or close to those during the evening rush hour and the morning rush hour. This result indicated that vehicular emissions play an important role in carbonaceous aerosols and PM2.5 during the nighttime. The above results provide insight into the quantitative evaluation of the contribution of vehicular emissions to OC, EC and PM2.5 and thus could provide references for pollution control in areas with high vehicular emissions.

Modeling the Optimal Transportation for Acute Stroke Treatment

PurposeProlonged transfer times between the primary stroke center (PSC) and the comprehensive stroke center (CSC) are one of the major causes of treatment delay for endovascular stroke treatment. We aimed to analyze the effect of the diurnal variations in traffic rates at weekdays and weekends on the catchment area size of three transportation paradigms, i.e. mothership, drip-and-ship (DS) and drip-and-drive (DD).MethodsA conditional probability model that predicts the probability of good outcome for patients with suspected large vessel occlusion was used to analyze the prehospital stroke triage in northwest Germany and produce catchment area maps. Transportation times were calculated during each hour of a weekday and a Sunday using Google Maps. For comparison, real DD transportation times from our CSC in Hamburg-Eppendorf (blinded for review) to a PSC in Lüneburg were prospectively recorded.ResultOn weekdays, the mothership catchment area was the largest (≥40,000 km2, 63%) except for a decrease during morning rush hours, when the DD catchment area was highest (30,879 km2, 48%). The DS catchment area was higher than the DD catchment area during the afternoon rush hours both during the week as well as on Sundays.ConclusionOur study showed a considerable impact of the diurnal variations in traffic rate and direction of travel on optimal stroke transportation. Stroke systems of care should take real time traffic information into account.

Dispersion Normalized PMF Provides Insights into the Significant Changes in Source Contributions to PM2.5 after the COVID-19 Outbreak.

Factor analysis utilizes the covariance of compositional variables to separate sources of ambient pollutants like particulate matter (PM). However, meteorology causes concentration variations in addition to emission rate changes. Conventional positive matrix factorization (PMF) loses information from the data because of these dilution variations. By incorporating the ventilation coefficient, dispersion normalized PMF (DN-PMF) reduces the dilution effects. DN-PMF was applied to hourly speciated particulate composition data from a field campaign that included the start of the COVID-19 outbreak. DN-PMF sharpened the morning coal combustion and rush hour traffic peaks and lowered the daytime soil, aged sea salt, and waste incinerator contributions that better reflect the actual emissions. These results identified significant changes in source contributions after the COVID-19 outbreak in China. During this pandemic, secondary inorganic aerosol became the predominant PM2.5 source representing 50.5% of the mean mass. Fireworks and residential burning (32.0%), primary coal combustion emissions (13.3%), primary traffic emissions (2.1%), soil and aged sea salt (1.2%), and incinerator (0.9%) represent the other contributors. Traffic decreased dramatically (70%) compared to other sources. Soil and aged sea salt also decreased by 68%, likely from decreased traffic.

A Study on Spatial and Temporal Aggregation Patterns of Urban Population in Wuhan City based on Baidu Heat Map and POI Data

Advanced technologies and big data have brought new visions and methods to urban planning research. Based on the Baidu heat map and POI data of two typical days (a weekend day and a workday) in 2018, this paper analyses the spatial and temporal aggregation patterns of crowds in the urban centre of Wuhan using ArcGIS. Aggregation patterns are defined by the intensity of population activities and the places where crowds gather. In terms of time, the daily change of population aggregation intensity is studied by counting the heat value of 24 moments captured throughout the day. The results show that on rest days, people prefer to travel around noon and in the afternoon, reaching the highest peak of the day around 15:00, while on workdays, residents' activities are affected by commuting, with obvious 'morning rush hours' and 'evening rush hours'. Firstly, the spatial correlation between the density of POI distribution and the degree of population aggregation has been studied by the spatial coupling relationship between the Baidu heat map and POI data. Secondly, the index of correlation between the aggregation of different POIs and population (ICPP) are mentioned to analyse the purposes and the degrees of aggregation during weekend and workday rush hours. Based on the ICPP, we analyse activities from three aspects: the different ICPPs between the workday and the weekend; the different ICPPs between the morning, afternoon and evening; and the different ICPPs among different POIs.

Investigation on Taxi Trip Characteristics Based on Taxi GPS Trajectory

Knowledge of urban taxi trip characteristics is crucial at many levels of urban transportation planning, operations, and traffic management. In this paper, we investigate the characteristics of taxi trip through analyzing approximately 3,000 taxis spanning seven consecutive days in Lanzhou. The characteristics of taxi trip such as taxi trip speed, service time, vacation time, and spatio-temporal patterns of taxi trip are analyzed. The results show that the average speed of taxis varies between 17 km/h to 22 km/h from 7 am to 8 pm. Moreover, the average service time and vacation time are 20 minutes and 6 minutes, respectively. Although, the net flow ratio in heart of the city goes around zero, the flow direction of taxi trip is obviously different in the morning rush and the evening rush. Moreover, The rural-urban fringes have a strong positive net flow ratio which indicates that the strength of inflow is greater than that of outflow.

Characteristics of urban air pollution in different regions of China between 2015 and 2019

The severity of urban air pollution problems in China increases with the city's size and population density. Outdoor air pollution not only affects indoor air quality but also increases building energy consumption. We analyzed the characteristics of urban air pollution in China based on long-period monitoring data with high temporal resolution (hourly) recorded between September 1, 2014 and August 31, 2019. We compared five key regions in detail: “2 + 26 cities,” the Yangtze River delta (YRD), the Pearl River delta (PRD), the Northeast China Plain (NECP), and the Sichuan Basin (SCB). The results show decreases in the annual mean concentrations of particulate matter, PM2.5 and PM10, SO2, and CO but an increase in the O3 concentration. The increasing O3 rate in the 2 + 26 cities region was nearly 14 times that of the global rate. In terms of diurnal variation, NO2 and CO reached maxima between 8:00 and 9:00 a.m. due to morning rush hour traffic, which was approximately 1 h before the PMs and SO2 reached their maxima. In the monthly variation profiles, the SO2 concentration magnitudes in the NECP were similar to those of the 2 + 26 cities during winter heating periods and the YRD region during the non-heating periods. Minima associated with “plum rain” and the rainy season were also observed in the O3 monthly variation profiles of the YRD and SCB regions, respectively. In the 2 + 26 cities region, each pollutant showed significantly large temporal variation relative to the spatial variation, which is indicative of the regional air pollution trend.

Pollution Characteristics of Atmospheric Carbonyls in Urban Linfen in Winter

Atmospheric carbonyls (aldehyde and ketone compounds) can be precursors for ozone and PM2.5, and they play an essential role in atmospheric chemistry. Linfen is a basin between mountains on the east and west, and there are many coking plants on the north and south sides of its urban area. The special topography and unfortunate industrial layout have frequently contributed to serious air pollution in Linfen. In order to investigate the pollution characteristics of atmospheric carbonyls in winter in urban Linfen, the carbonyl compounds were collected from the Municipal Committee site (MC) and the Yaowangtai site (YWT) from 16 to 25 January 2019, and their concentrations were analyzed by a high performance liquid chromatography-ultraviolet detector (HPLC-UV). The results show that formaldehyde, acetaldehyde, and acetone were the most abundant compounds, accounting for more than 70% of the total mass concentration of carbonyls in urban Linfen. Levels of these three carbonyls increased during the morning and evening traffic rush hours. The mass concentration of formaldehyde at both sites reached peak values at around noon (10:00–14:00). In addition, the mass concentrations of formaldehyde, acetaldehyde, and acetone were positively correlated with CO mass concentrations, whereas only formaldehyde and acetaldehyde were positively correlated with temperature. Therefore, atmospheric formaldehyde in urban Linfen’s winter mainly came from vehicle exhaust emissions and the secondary generation of photochemical reactions. Most of the acetaldehyde came from vehicle exhaust emissions, and photochemical reactions also partially contributed to it. For acetone, vehicle exhaust emissions were the main source. In addition, coking industry emissions from Northern Linfen′s Hongtong County may also have contributed to the atmospheric carbonyls in the urban area of Linfen. For the first time, this study found that formaldehyde showed different behavior to acetaldehyde and acetone; that is, the nighttime decrease in formaldehyde mass concentration was greater than that of acetaldehyde and acetone.