Spatio-temporal characteristics of PM2.5 and O3 synergic pollutions and influence factors in the Yangtze River Delta

Since the implementation of pollution prevention and control action in China in 2013, particulate pollution has been greatly reduced, while ozone pollution has become gradually severe, especially in the economically developed eastern region. Recently, a new situation of air pollution has emerged, namely, enhanced atmospheric oxidation, ascending regional ozone pollution, and increasing particle and ozone synergic pollution (i.e., double-high pollution). Based on the long-term observation data from 2015 to 2021, we examined the spatio-temporal characteristics of urban PM2.5 and O3 pollution in the Yangtze River Delta and quantified the effects of meteorological and non-meteorological factors on pollution in four city clusters using stepwise multiple linear regression models. Temporally, PM2.5 decreased gradually year by year while, O3 increased in city clusters. Spatially, PM2.5 declined from northwest to southeast, while O3 decreased from northeast to southwest. Except for southern Zhejiang, other city clusters suffer from complex air pollution at different levels. In general, pollution intensity and frequency vary with city location and time. Single PM2.5 pollution mostly occurred in northern Anhui. Single O3 pollution occurred in central and southern Jiangsu and northern Zhejiang. Synergic pollutions of PM2.5 and O3 mainly occurred in central Jiangsu. The contributions (90%) of non-meteorological factors (e.g., anthropogenic emission) to PM2.5 decrease and O3 increase are far larger than that of meteorological factors (5%). Relative humidity, sea level pressure, and planetary boundary layer height are the most important meteorological factors to drive PM2.5 changes during pollution. Downward solar radiation, total cloud cover, and precipitation are the most important meteorological factors that affect O3 changes during pollution. The results provide insights into particulate and ozone pollution in the Yangtze River Delta and can help policymakers to formulate accurate air pollution prevention and control strategies at urban and city cluster scales in the future

Comparison of diffusion-weighted MRI acquisition techniques for normal pancreas at 3.0 Tesla

PURPOSEWe aimed to optimize diffusion-weighted imaging (DWI) acquisitions for normal pancreas at 3.0 Tesla.MATERIALS AND METHODSThirty healthy volunteers were examined using four DWI acquisition techniques with b values of 0 and 600 s/mm2 at 3.0 Tesla, including breath-hold DWI, respiratory-triggered DWI, respiratory-triggered DWI with inversion recovery (IR), and free-breathing DWI with IR. Artifacts, signal-to-noise ratio (SNR) and apparent diffusion coefficient (ADC) of normal pancreas were statistically evaluated among different DWI acquisitions.RESULTSStatistical differences were noticed in artifacts, SNR, and ADC values of normal pancreas among different DWI acquisitions by ANOVA (P < 0.001). Normal pancreas imaging had the lowest artifact in respiratory-triggered DWI with IR, the highest SNR in respiratory-triggered DWI, and the highest ADC value in free-breathing DWI with IR. The head, body, and tail of normal pancreas had statistically different ADC values on each DWI acquisition by ANOVA (P < 0.05).CONCLUSIONThe highest image quality for normal pancreas was obtained using respiratory-triggered DWI with IR. Normal pancreas displayed inhomogeneous ADC values along the head, body, and tail structures

Particle Size Distributions of Oxidative Potential of Lung-Deposited Particles: Assessing Contributions from Quinones and Water-Soluble Metals

Redox-active species in ambient particulate matter (PM) cause adverse health effects through the production of reactive oxygen species (ROS) in the human respiratory tract. However, respiratory deposition of these species and their relative contributions to oxidative potential (OP) have not been described. Size-segregated aerosols were collected during haze and nonhaze periods using a micro-orifice uniform deposit impactor sampler at an urban site in Shanghai to address this issue. Samples were analyzed for redox-active species content and PM OP. The average dithiothreitol (DTT) activity of haze samples was approximately 2.4-fold higher than that of nonhaze samples and significantly correlated with quinone and water-soluble metal concentrations. The size-specific distribution data revealed that both water-soluble OP_v^DTT (volume-normalized OP quantified by DTT assay) and OP_m^DTT (mass-normalized OP) were unimodal, peaking at 0.56–1 and 0.1–0.32 μm, respectively, due to contributions from accumulation-mode quinones and water-soluble metals. We further estimated that transition metals (mainly copper and manganese) contributed 55 ± 13% of the DTT activity while quinones accounted for only 8 ± 3%. Multiple-path particle dosimetry calculations estimated that OP deposition in the pulmonary region was mainly from accumulation-mode transition metals despite quinones having the highest DTT activity. This behavior is primarily attributed to the efficiency of deposition of transition metals in the pulmonary region being approximately 1.2-fold greater than that of quinones. These results reveal that accumulation-mode transition metals are significant contributors to the OP of deposited water-soluble particles in the pulmonary region of the lung

Simulating the Effects of Urban Parameterizations on the Passage of a Cold Front During a Pollution Episode in Megacity Shanghai

Urbanization significantly influences meteorological conditions and air quality. Statistically, air pollution in the megacity of Shanghai usually occurs with cold weather fronts. An air pollution episode during a cold front was simulated using weather research and forecasting and the Community Multi-scale Air Quality model system. In this study, we used two urban schemes, a simple bulk scheme (denoted BULK) and the single-layer urban canopy model (SLUCM), to check the effects of urban parameterization. Our results showed that SLUCM better predicted the arrival time and cooling process of the cold front and more realistically simulated the moving process of the cold front. The improvement in the temperature and relative humidity simulation achieved using SLUCM was more effective under higher urbanization levels, whereas the wind speed simulation was better in rural areas. The simulated concentrations at sites with high urbanization were obviously improved by urban parameterization. The barrier role of the urban canopy during a cold front was better represented and was shown to cause a wider polluted area and higher pollutant concentration using SLUCM than with BULK. Overall, accurate meteorological simulations in the atmospheric boundary layer using SLUCM are expected to provide good prediction of urban air quality

The role of ASM on the formation and properties of cirrus clouds over the Tibetan Plateau

Cirrus clouds play a significant role in the Earth’s energy balance and in the hydrological cycle of the atmosphere. Here, a high-performance Micro Pulse Lidar was continuously used to investigate cirrus cloud formation and characteristics at Ali (32.50°N, 80.08°E; 4279 m), in the western Tibetan Plateau from 25 July to 23 September 2016, a time frame that spanned the prevalence and degeneration period of the Asian summer monsoon (ASM). The cirrus clouds frequently occurred with sharp fluctuations in the vertical distribution from 8 to 14 km above ground level (AGL) during the ASM period. In contrast, cirrus clouds were remarkably reduced and consistently existed near 10 km in September, when the ASM began subsiding due to the lack of a driving force that triggers ice formation. Approximately half of the cirrus clouds were caused by deep convective activity during the ASM period, which held one-third of total cirrus clouds during the whole measurement period. These anvil cirrus clouds have a liquid origin and are characterised by optically thicker clouds with Cloud Optical Depth values greater than 0.2, high depolarisation ratios and high lidar ratios. These observations indicate that, in agreement with other studies at mid-latitudes and in the Arctic, liquid origin cirrus could be associated with thicker, larger and more complex nonspherical ice crystals in comparison to in situ formed cirrus. Cold perturbations were responsible for the formation and evolution of the remaining two-thirds of cirrus clouds. These clouds were mostly associated with in situ formation of ice crystals, in the slow updrafts in the tropical transition layer over the Tibetan Plateau

Urban Aerosol Characteristics during the World Expo 2010 in Shanghai

International audienceDuring the World Exposition 2010, which ran from May to October, emission control measures were implemented inShanghai and surrounding areas to improve the air quality. This study evaluated the effects of regional transport on aerosolcharacteristics under these controlled local emission conditions using a month’s worth of observations of the aerosol numbersize distributions (10 nm–10 μm) and the chemical compositions of the aerosols. Back-trajectories and a Lagrangiandispersion model were combined to analyze the transport characteristics of regional and local air pollution and the relatedmechanisms. Two classes of aerosols were identified and compared. Class I was a clear air condition with ocean-oriented airmasses. Particle counts in this class were dominated by particles in the size range 20–40 nm, and NH4+ was mainly presentin the form of (NH4)2SO4. A strong peak at noontime indicated that the particle formation or growth process was promotedby the photochemical process. Class II was characterized as a regional transport pollution condition with air massesoriginating in the surrounding areas. The analysis showed increases in particle number concentrations and total watersoluble ions of about 17% and 350%, respectively, compared with Class I episodes. The fraction of particles in the size range50–200 nm increased sharply to almost 50% of the total particle counts. An examination of the diurnal pattern and majorwater soluble ions suggested that the increase in size mode (50–200 nm) particles was mainly due to the particle growthprocess and the presence of enough precursor gases. NH4+ was present in the form of (NH4)2SO4 and NH4NO3. Althoughair control measures during the World Expo significantly limited local emissions, our results indicate that the regionaltransport from surrounding cities was responsible for the higher trace gases and particle volume concentrations, along withthe large number of Aitken mode particles

Observational evidence of particle hygroscopic growth in the upper troposphere-lower stratosphere (UTLS) over the Tibetan Plateau

We measured the vertical profiles of backscatter ratio (BSR) using the balloon-borne, lightweight Compact Optical Backscatter AerosoL Detector (COBALD) instruments above Linzhi, located in the southeastern Tibetan Plateau, in the summer of 2014. An enhanced aerosol layer in the upper troposphere–lower stratosphere (UTLS), with BSR (455 nm) > 1.1 and BSR (940 nm) > 1.4, was observed. The color index (CI) of the enhanced aerosol layer, defined as the ratio of aerosol backscatter ratios (ABSRs) at wavelengths of 940 and 455 nm, varied from 4 to 8, indicating the prevalence of fine particles with a mode radius of less than 0.1 µm. We find that unlike the very small particles (mode radius smaller than 0.04 µm) at low relative humidity (RHi < 40 %), the relatively large particles in the aerosol layer were generally very hydrophilic as their size increased dramatically with relative humidity. This result indicates that water vapor can play a very important role in increasing the size of fine particles in the UTLS over the Tibetan Plateau. Our observations provide observation-based evidence supporting the idea that aerosol particle hygroscopic growth is an important factor influencing the radiative properties of the Asian Tropopause Aerosol Layer (ATAL) during the Asian summer monsoon.ISSN:1680-7375ISSN:1680-736

Interactions between Heterogeneous Uptake and Adsorption of Sulfur Dioxide and Acetaldehyde on Hematite

Sulfur dioxide and organic aldehydes in the atmosphere are ubiquitous and often correlated with mineral dust aerosols. Heterogeneous uptake and adsorption of one of these species on mineral aerosols can potentially change the properties of the particles and further affect the subsequent heterogeneous reactions of the other species on the coating particles. In this study, the interactions between heterogeneous uptake and adsorption of sulfur dioxide and acetaldehyde on hematite are investigated by using in situ diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS) at room temperature. It is found that the preadsorption of SO₂ on α-Fe₂O₃ can significantly hinder the subsequent heterogeneous oxidation of CH₃CHO to acetate, while the preadsorption of CH₃CHO significantly suppresses the heterogeneous reaction of large amounts of SO₂ on the surface of α-Fe₂O₃ and has a little influence on the uptake of small amount of SO₂. The heterogeneous reactions of SO₂ on α-Fe₂O₃ preadsorbed by CH₃CHO change the existing acetate on the particle surface into chemisorbed acetic acid, for the enhancement of surface acidity after the uptake of SO₂. During these processes, different surface hydroxyl groups showed different reactivities. Atmospheric implications of this study are discussed