Formation Mechanism Of Pollution Research Articles

Formation Mechanism and Optimization Method of Streak-Shaped Pollution for the Roof Insulator of EMUs

Roof insulators are one of the key pieces of equipment to ensure the electrical safety of high-speed railways (HSRs). When the umbrella skirt of a roof insulator is seriously polluted in various environments, the risk of pollution-induced flashover rises. Field experience shows that the flashover possibility of roof insulators in coastal intercity railways is much higher than that in other regions. However, the pollution characteristics of roof insulators under those conditions are still unclear. In this work, we investigated the pollution characteristics of roof insulators used in the coastal intercity railway of electric multiple units (EMUs) of China. Aspects of the pollution spatial distribution, the statistical content, and the pollution constituent on the surface of the umbrella skirt of insulators are taken into account. The airflow field and electric field distribution around the pantograph support insulator (PSI) are also simulated based on finite element software. To reduce the formation of streak-shaped pollution, the umbrella skirt is optimized by the streamlined structure. The results indicate that a novel phenomenon of streak-shaped pollution distribution might form on the surface of the insulator, which would severely aggravate the distortion of electric field distribution. The calculated turbulence dissipation rates are found to spatially agree well with the streak-shaped pollution distribution. The streamlined structure effectively reduces the turbulence dissipation rate at the junction of the windward and leeward surfaces, to inhibit the formation of streak-shaped pollution.

Experimental and numerical investigation of flame stabilization and pollutant formation in matrix stabilized ammonia-hydrogen combustion

Ammonia (NH3) is a carbon-free fuel that offers an attractive alternative for reducing greenhouse gas emissions. However, the slow flame speed, low heating value, and emissions of nitrogen-containing pollutants present significant issues for practical combustion applications. To address these issues, we investigate the use of matrix stabilized combustion. In this type of burner, combustion is performed within an inert porous ceramic foam, heat is recirculated by solid conduction and radiation, which enhances flame speed and combustion stabilization, thereby permitting combustion over a wide range of equivalence ratio conditions. We present a new porous media burner (PMB) capable of stabilizing NH3/air flames at ambient conditions. An extensive experimental characterization of the stability of this burner is conducted with up to 30% by volume of hydrogen (H2) in the fuel stream. A 15:1 turndown ratio is demonstrated, with a high thermal power density of 62MWm−3. Concentrations of NO, unburnt NH3, and H2 in the exhaust stream are measured. Two regimes are identified for low NO operation: rich and very lean. For rich conditions, NO emissions decrease with increasing equivalence ratio and decreasing H2 blending. Unburnt NH3 emissions follow opposite trends. These measurements are complemented by simulations in which the burner is represented by a coupled solid-gas reactor network. This model captures the burner’s pollutant emissions to good accuracy and is used to analyze the mechanisms of pollutant formation.

Free radical mechanism of toxic organic compound formations from o-chlorophenol.

Organic free radical intermediates are pivotal to our understanding of toxic chemicals formation from chlorophenols that widely exist in thermal processes. However, in most cases, multiple free radical intermediates exist and produce complex spectra that are hard to deconvolute. Identification of free radical intermediates is the current difficulty for detailed formation mechanisms of toxic products from chlorophenols. In this study, a universal bottom-up method was developed to identify the organic free radical intermediates. Candidate organic free radicals were firstly speculated according to the critical parameters obtained from experimental electron paramagnetic resonance (EPR) spectra and the calculated bond dissociation energies of precursors. Their theoretical spectra were then used retrospectively to justify the accordance with the experimental EPR spectra. Identification of the organic free radicals provides straightforward evidence for the formation pathways of pollutants from chlorophenol. Internal factors influencing formation of radical intermediates and the toxic products were also studied, including the ortho effect of the precursor, spin densities of the organic free radical intermediates, and steric hindrance effects of the molecular intermediates. In combination of the experimental results and theoretical calculations, detailed formation mechanisms of toxic pollutants intermediating by organic free radicals from thermal oxidation of chlorophenol were strongly evidenced.

Exploring the formation mechanism of fine particles in an ex-heavily polluted Northwestern city, China

Fine particle pollution is still a severe issue in the northwestern region of China where the formation mechanism of which remains ambiguous due to the limited studies there. In this study, a comprehensive study on the chemical composition and sources of PM2.5 at an ex-heavily polluted northwestern city was conducted, based on filter sampling data obtained from three consecutive winter campaigns during 2020–2022. The average PM2.5 during the three winter campaigns were 170.9 ± 66.4, 249.0 ± 75.7, and 200.9 ± 47.6 μg/m3, respectively, with the daily maximum value of PM2.5 exceeds 400 μg/m3 under stagnant meteorological conditions charactered by high relative humidity (>60 %) and low wind speed (<1 m/s). The major chemical components in PM2.5 were found to be inorganic aerosol (55.2 %) that mainly constituted by sulfate (24.2 %), and mineral dust (14.9 %); while the carbonous species contributed a minor fraction (∼13 %). In addition, (NH4)2SO4 and NH4NO3 were the dominate contributors to appearance of low visibility (<3 km) which together accounting for over 85 % of light extinction coefficient (bext) during heavy polluted period. Source appointment of fine particles was then conducted by applying the positive matrix factorization method, and the primary sources were resolved to be coal combustion (27.7 %) and biomass burning (18.6 %), followed by industrial dust (16.2 %), residential combustion (15.3 %), traffic emissions (11.9 %) and dust aerosol (10.4 %). To explore the potential formation mechanism of fine particle pollution, the chemical evolution pattern combined with gaseous pollutants and meteorological parameters were further analyzed, which refine the important role of primary emissions in the forming of high sulfate aerosol loading, while secondary formation was largely suppressed during the winter period that totally different from those reported in the developed regions of China, thus indicating more effort should be paid on the reduction of primary particles emissions in the northwestern cities than on its gaseous percussors.

Pollution formation and the response of premixed hydrogen blending flame to the external excitation using large eddy simulation: The application of an artificial neural network and genetic algorithm

BackgroundThe regulations for combustion pollution are getting more stringent every day. To decrease the level of pollution, serious attention to the unstable operating conditions of the flame is essential, as any flame may suffer from a level of instability. Further, the application of hydrogen-hydrocarbon blending fuels is developing in the industries. MethodsTherefore, the current study investigates the pollution produced by unstable combustion. An artificial neural network applying 4-15-1 neurons is also used by the input parameters of excitation frequency, amplitude, equivalence ratio, and hydrogen content. It is shown that the prediction is well for emissions. Using a genetic algorithm, the operating conditions corresponding to a minimum pollution emission are determined. Additionally, the importance of the governing parameters is evaluated in the pollution formation mechanism, and the excitation frequency is set in the first rank. Significant findingsHydrogen addition makes the NOx to be increased by a factor of 2.5 and CO to be mitigated by a rate of 2. This factor for increasing the excitation amplitude from 0.05 to 0.45 is around 5. Furthermore, the flame response to the inlet excitation is completely assessed using the heat release fluctuation, transfer function magnitude, and phase. Adding more hydrogen was shown to shift the cut-off frequency.

New insight into formation mechanism, source and control strategy of severe O3 pollution: The case from photochemical simulation in the Wuhan Metropolitan Area, Central China

The Wuhan Metropolitan Area, located in Central China, has experienced severe O3 pollution in recent years; thus urging to diagnose formation regime and propose reasonable control strategies. Multi-source data of air pollutants and meteorological factors in 4 cities during August 2019 when severe regional O3 pollution occurred were obtained; then, in-situ O3 formation mechanism, the O3-precursors sensitivity, the sources and control strategies of O3 were evaluated based on the combination of the 0-D photochemical observation-based model and the positive matrix factorization model through the analysis of local ozone budget, the relative incremental reactivity, an empirical kinetic model approach and source apportionment. The results indicated the P(O3) (net O3 production rate) was 25 ppbv h−1 in Ezhou and 11–13 ppbv h−1 in other 3 cities. The dominated photochemical production of O3 was NO + HO2 reaction (62–71%), whereas the main pathway to destroy O3 during daytime was NO2 + OH (>70%) and nocturnal loss of O3 with alkenes even reached up to 39–46%. Generally, O3 formation was sensitive to AVOC (Anthropogenic Volatile Organic Compounds), in which reactive aromatics, OVOCs (Oxygenated VOCs), and alkenes (xylenes, ethylene, isoprene, methyl vinyl ketone, hexanal, toluene and methacrolein, specifically) as well as abundant i-pentane should be targeted to alleviate O3 pollution. The highly reactive VOCs sources for O3 formation in this region were vehicular exhaust (28–41%), industrial emissions (20–29% except Ezhou), and solvent use (17–29% except Huangshi). Co-reduction of O3 precursors in aforementioned reactive emissions according to optimal ratios of AVOC to NO2, i.e., 5:1 (Wuhan and Huanggang), 4:1 (Ezhou), and 6:1 (Huangshi), could achieve local O3 effective mitigation. Surprisingly, P(O3) could reduce by 38% and 48% under 40% AVOC cut accompanied by NO2 in more contaminated cities (Wuhan and Ezhou). Overall, our study provides new insight to future collaborative O3 alleviation strategies formulation in Central China, which quantified O3 formation at different precursors levels in different cities suffering from regional O3 pollution, concluded best precursors control ratios and confirmed validity of O3 mitigation through precursors-oriented emission reduction in vital sources.

Pollution mechanisms and photochemical effects of atmospheric HCHO in a coastal city of southeast China

Formaldehyde (HCHO) is a vital reactive carbonyl compound, which plays an important role in the photochemical process and atmospheric oxidation capacity. However, the current studies on the quantification of HCHO impacts on atmospheric photochemistry in southeast coastal areas of China with an obvious upward trend of ozone remain scarce and unclear, thus limiting the full understanding of formation mechanism and control strategy of photochemical pollution. Here, systematic field campaigns were conducted at a typical coastal urban site with good air quality to reveal HCHO mechanism and effects on O3 pollution mechanism during spring and autumn, when photochemical pollution events still frequently appeared. Positive Matrix Factorization model results showed that secondary photochemical formation made the largest contributions to HCHO (69 %) in this study. Based on the photochemical model, the HCHO loss rates in autumn were significantly higher than those in spring (P < 0.05), indicating that strong photochemical conditions constrain high HCHO levels in certain situations. HCHO mechanism increased the ROx concentrations by 36 %, and increased net O3 production rates by 31 %, manifesting that the reduction of HCHO and its precursors' emissions would effectively mitigate O3 pollution. Therefore, the pollution characteristics and photochemical effects of HCHO provided significant guidance for future photochemical pollution control in relatively clean areas.

The Influence of Synoptic Weather Patterns on Spatiotemporal Characteristics of Ozone Pollution Across Pearl River Delta of Southern China

AbstractTropospheric ozone (O3) pollution is becoming the primary obstacle to the improvement of air quality in China, especially in the Pearl River Delta (PRD) region. Because O3 pollution episodes are closely related to synoptic weather patterns (SWPs), historical episodes (from 2006 to 2019) were classified according to SWPs using the Lamb‐Jenkinson method. Monitoring network and weather reanalysis data, emission inventories, and satellite retrievals were used to investigate the spatiotemporal characteristics and influences of O3 pollution. It was found that easterly (P_E), anticyclone (P_A), and typhoon‐related (P_NE) SWPs accounted for 75% of all O3 pollution episodes. In the PRD, the O3 formation mechanism showed clear differences under different SWPs, which were affected by local emissions under P_A, whereas regional transmission dominated under P_E and P_NE. The O3 peak concentration was strongly associated with temperature, solar radiation, and shifting of the sea‐land breeze. A delayed shift of land to sea breeze caused by SWPs often caused the O3 peak to appear in the late afternoon. Finally, stepwise regression was used to explain individual meteorological parameters contributing to O3 formation. It was found that the formation of O3 pollution under P_E and P_NE was associated with increases in temperature and radiation, while P_A was mainly affected by the increase of the overnight accumulation of O3. This study advances our knowledge of the formation mechanism of O3 pollution and provides scientific support for effective O3 pollution control.

A vehicle-mounted dual-smog chamber: Characterization and its preliminary application to evolutionary simulation of photochemical processes in a quasi-realistic atmosphere

Smog chambers are the effective tools for studying formation mechanisms of air pollution. Simulations by traditional smog chambers differ to a large extent from real atmospheric conditions, including light, temperature and atmospheric composition. However, the existing parameters for mechanism interpretation are derived from the traditional smog chambers. To address the gap between the traditional laboratory simulations and the photochemistry in the real atmosphere, a vehicle-mounted indoor-outdoor dual-smog chamber (JNU-VMDSC) was developed, which can be quickly transferred to the desired sites to simulate quasi-realistic atmosphere simultaneously in both chambers using “local air”. Multiple key parameters of the smog chamber were characterized in the study, demonstrating that JNU-VMDSC meets the requirements of general atmospheric chemistry simulation studies. Additionally, the preliminary results for the photochemical simulations of quasi-realistic atmospheres in Pearl River Delta region and Nanling Mountains are consistent with literature reports on the photochemistry in this region. JNU-VMDSC provides a convenient and reliable experimental device and means to study the mechanism of atmospheric photochemical reactions to obtain near-real results, and will make a great contribution to the control of composite air pollution.

The Chinese Spring Festival Impact on Air Quality in China: A Critical Review

It is known that the sharp change of air pollutants affects air quality. Chinese Spring Festival is the most important holiday for Chinese people, and the celebration of the holiday with fireworks and the movement of people all around the country results in significant change in multiple air pollutant emissions of various sources. As many cities and rural areas suffer from the air pollution caused by firework displays and more residential fuel consumption, there is an urgency to examine the impact of the Chinese Spring Festival on air quality. Hence, this paper firstly gives an overall insight into the holiday’s impact on ambient and household air quality in China, both in urban and rural areas. The main findings of this study are: (1) The firework displays affect the air quality of urban and rural atmosphere and household air; (2) the reduction in anthropogenic emissions improves the air quality during the Chinese Spring Festival; (3) the household air in urban areas was affected most by firework burning, while the household air in rural homes was affected most by fuel consumption; and (4) the short-term health impact of air pollution during the holidays also need more concern. Although there have been many publications focused on the holiday’s impact on ambient and household air quality, most of them focused on the measurement of pollutant concentration, while studies on the formation mechanism of air pollution, the influence of meteorological conditions, and the health outcome under the effect of the Chinese Spring Festival are rare. In the future, studies focused on these processes are welcomed.

Compilation of reaction kinetics parameters determined in the Key Development Project for Air Pollution Formation Mechanism and Control Technologies in China

A compilation of new advances made in the research field of laboratory reaction kinetics in China's Key Development Project for Air Pollution Formation Mechanism and Control Technologies was presented. These advances are grouped into six broad, interrelated categories, including volatile organic compound (VOC) oxidation, secondary organic aerosol (SOA) formation, new particle formation (NPF) and gas-particle partitioning, ozone chemistry, model parameters, and secondary inorganic aerosol (SIA) formation, highlighting the laboratory work done by Chinese researchers. For smog chamber applications, the current knowledge gained from laboratory studies is reviewed, with emphasis on summarizing the oxidation mechanisms of long-chain alkanes, aromatics, alkenes, aldehydes/ketones in the atmosphere, SOA formation from anthropogenic emission sources, and oxidation of aromatics, isoprene, and limonene, as well as SIA formation. For flow tube applications, atmospheric oxidation mechanisms of toluene and methacrolein, SOA formation from limonene oxidation by ozone, gas-particle partitioning of peroxides, and sulfuric acid-water (H2SO4-H2O) binary nucleation, methanesulfonic acid-water (MSA-H2O) binary nucleation, and sulfuric acid-ammonia-water (H2SO4-NH3-H2O) ternary nucleation are discussed.

Correlation between biomass burning and air pollution in China: Spatial heterogeneity and corresponding factors

Biomass burning (i.e., forest fires or open-field burning) is strongly correlated with regional air pollution. However, the correlation varied in different regions because of the complex interaction with other driving factors, leaving a substantial gap in understanding the mechanism of air pollution formation. This study aimed to clarify the spatial heterogeneity and corresponding factors of the biomass burning-air pollution correlation in China in recent decades (2001–2019). Multisource datasets, including satellite observations, in situ measurements, and annual statistics, were adopted for the evaluation through mathematical statistics and spatial-temporal analysis. The results showed that biomass burning mainly occurred in Northeast, Central and South China, which decreased slightly by −153.08 km 2 ·yr −1 during the study period. Under this background, air quality improved significantly, particularly after 2013. The strongest correlations occurred in Northeast China at the spatial scale or in spring at the temporal scale. Notably, the correlation was affected by several factors and their complex interactions. Specifically, the dominant factors of the correlations were gross domestic product (GDP) in Northeast China, atmospheric humidity in Central China, and population in South China. In addition, these factors exerted significant interactions, which were characterized by the two-factor enhancement of temperature-GDP in Northeast China, the nonlinear enhancement of temperature-DEM in Central China, and the nonlinear enhancement of temperature-population in South China. The results of this study were helpful for capturing the physical correlation between biomass burning and air pollution, which would further support relevant air pollution management and control. • Biomass burning impact on air pollution were evaluated in pixel-wise. • Strong correlations located in Northeast, Central and South China. • Dominant factors were GDP, humidity and population in three hotspots regions. • Interactions had a stronger effect on correlation than single factors.

Temporal Variation of NO2 and HCHO Vertical Profiles Derived from MAX-DOAS Observation in Summer at a Rural Site of the North China Plain and Ozone Production in Relation to HCHO/NO2 Ratio

We performed a comprehensive and intensive field experiment including ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurement at Raoyang (115°44′ E, 38°14′ N; 20 m altitude) in summer (13 June–20 August) 2014. The NO2 and HCHO profiles retrieved by MAX-DOAS take on different vertical distribution shapes, with the former declining with the increasing altitude and the latter having an elevated layer. The average levels of vertical column densities (VCDs) and near-surface volume mixing ratios (VMRs) were 1.02 ± 0.51 × 1016 molec·cm−2 and 3.23 ± 2.70 ppb for NO2 and 2.32 ± 0.56 × 1016 molec·cm−2 and 5.62 ± 2.11 ppb for HCHO, respectively. The NO2 and HCHO levels are closely connected with meteorological conditions, with the larger NO2 VCDs being associated with lower temperature, higher relative humidity (RH) and lower planetary boundary layer height (PBLH). With respect to the diurnal variations of vertical distribution, the NO2 in the residual layer gradually disappeared from 1.2 km height to the surface during the period of 7:00–11:00 Beijing time (BJ), and the near-surface NO2 had larger VMRs in the early morning and evening than in the later morning and afternoon. An elevated HCHO layer was observed to occur persistently with the lifted layer height rising from ~0.5 km to ~1.0 km before 10:00 BJ; the near-surface HCHO VMRs gradually increased and peaked around 10:00 BJ. The ratios of HCHO to NO2 (RHCHO-NO2) were generally larger than two in the boundary layer from 11:00 BJ until 19:00 BJ, the time period when ozone photochemistry was most active. Thus, ozone (O3) production was mainly in the NOx-limited regime during the observation campaign, which was closely related to relatively high temperatures and low RH. The O3 production regimes also changed with the wind’s direction. These results are significant to reveal the formation mechanism of O3 pollution and develop strategies for controlling the O3 photochemical pollution over the North China Plain.

A Comprehensive Study of a Winter Haze Episode over the Area around Bohai Bay in Northeast China: Insights from Meteorological Elements Observations of Boundary Layer

Based on wind profile radar observations, along with high-frequency wave radar data, meteorological data, and air quality monitoring data, we studied a haze episode in Panjin—a coastal city around Bohai Bay in Northeast China—that occurred from 8 to 13 February 2020. The results show that this persistent pollution event was dominated by PM10 and PM2.5 and their mass concentrations were both ~120 μg/m3 in the mature stage. In the early stage, the southerly sea breeze of ~4.5 m/s brought a large amount of moist air from the sea, which provided sufficient water vapor for the condensation and nucleation of pollutants, and thus accelerated the formation of haze. In the whole haze process, a weak updraft first appeared in the boundary layer, according to the vertical profile, contributing to the collision and growth of particulate matter. Vertical turbulence was barely observed in the mature stage, with the haze layer reaching 900 m in its peak, suggesting stable stratification conditions of the atmospheric boundary layer. The explosive growth of pollutant concentrations was about 10 h later than the formation of the stable stratification condition of the boundary layer. The potential source areas of air pollutants were identified by the WRF-FLEXPART model, which showed the significant contribution of local emissions and the transport effect of sea breeze. This study provides insights into the formation mechanism of haze pollution in this area, but the data observed in this campaign are also valuable for numerical modeling.

Characteristics and pollution formation mechanism of atmospheric fine particles in the megacity of Chengdu, China

To investigate the characteristics and pollution formation mechanism of fine particles in the atmosphere of Chengdu, one of the cities most affected by haze in China, ambient single aerosol particles were measured by single particle aerosol mass spectrometry from April to May 2021. All particles collected during the study period could be divided into seven categories: Dust, vehicle emission (VE), biomass burning (BB), coal combustion (CC), organic carbon (OC), K-nitrate (KNO3) and K-sulfate (KSO4) particles. BB and VE particles contributed 29.2% and 25.0% to the total particles, respectively, and these two types of particles can be used as the focus of pollution reduction in the future. The mixed state analysis showed that all types of particles highly mixed with their tracer ions, and the non secondary inorganic particles (i.e., Dust, VE, BB, CC and OC particles) showed stronger mixing with nitrate than sulfate. The increase of PM2.5 concentration can be divided into three stages, and the increase of PM2.5 concentration in these three stages was dominated by Dust and OC particles, BB and KNO3 particles, and the remaining three types of particles, respectively. The air masses mainly originated from the area northeast of Chengdu, while the southwest trajectory corresponded to the highest PM2.5 and PM10 concentrations. Meanwhile, the potential source areas of the different types of particles were different and the area southwest of Chengdu was the most important potential source of PM2.5 and of most particle types.

Atmospheric Particle Hygroscopicity and the Influence by Oxidation State of Organic Aerosols in Urban Beijing

A hygroscopic tandem differential mobility analyser (H-TDMA) was used to observe the size-resolved hygroscopic characteristics of submicron particles in January and April 2018 in urban Beijing. The probability distribution of the hygroscopic growth factor (HGF-PDF) in winter and spring usually showed a bimodal pattern, with more hygroscopic mode (MH) being more dominant. The seasonal variation in particle hygroscopicity was related to the origin of air mass, which received polluted southerly air masses in spring and clean northwesterly air masses in winter. Particles showed stronger hygroscopic behaviour during heavy pollution episodes (HPEs) with elevated concentrations of secondary aerosols, especially higher mass fraction of nitrate, which were indicated using the PM2.5 (particulate matter with diameter below 2.5 µm) mass concentration normalised by CO mass concentration. The hygroscopic parameter (κ) values were calculated using H-TDMA (κhtdma) and chemical composition (κchem). The closure study showed that κchem was overestimated in winter afternoon when compared with κhtdma, because the organic particle hygroscopic parameter (κorg) was overestimated in the calculations. It was influenced by the presence of a high concentration of hydrocarbon-like organic aerosol (HOA) with a weak water uptake ability. A positive relationship was observed between κorg and the ratio of oxygenated organic aerosol (OOA) and HOA, thereby indicating that the strong oxidation state enhanced the hygroscopicity of the particles. This study revealed the effect of local emission sources and secondary aerosol formation processes on particle hygroscopicity, which is of great significance for understanding the pollution formation mechanism in the North China Plain.

New Insight into Formation Mechanism, Source and Control Strategy of Severe O3 Pollution: The Case from Photochemical Simulation in the Wuhan Metropolitan Area, Central China

New Insight into Formation Mechanism, Source and Control Strategy of Severe O3 Pollution: The Case from Photochemical Simulation in the Wuhan Metropolitan Area, Central China

Persistent pollution episodes, transport pathways, and potential sources of air pollution during the heating season of 2016-2017 in Lanzhou, China.

As one of the most important industrial cities in Northwest China, Lanzhou currently suffers from serious air pollution. This study analyzed the formation mechanism and potential source areas of persistent air pollution in Lanzhou during the heating period from November 1, 2016 to March 31, 2017 based on the air pollutant concentrations and relevant meteorological data. Our findings indicate that particulate pollution was extremely severe during the study period. The daily PM2.5 and PM10 concentrations had significantly negative correlations with daily temperature, wind speed, maximum daily boundary layer height, while the daily PM2.5 and PM10 concentrations showed significantly positive correlations with daily relative humidity. Five persistent pollution episodes were identified and classified as either stagnant accumulation or explosive growth types according to the mechanism of pollution formation and evolution. The PM2.5 and PM10 concentrations and PM2.5/PM10 ratio followed a growing "saw-tooth cycle" pattern during the stagnant accumulation type event. Dust storms caused abrupt peaks in PM10 and a sharp decrease in the PM2.5/PM10 ratio in explosive growth type events. The potential sources of PM10 were mainly distributed in the Kumtag Desert in Xinjiang Uygur Autonomous Region, the Qaidam Basin and Hehuang Valley in Qinghai Province, and the western and eastern Hexi Corridor in Gansu Province. The contributions to PM10 were more than 120μg/m3. The important potential sources of PM2.5 were located in Hehuang Valley in Qinghai and Linxia Hui Autonomous Prefecture in Gansu; the concentrations of PM2.5 were more than 60μg/m3.

Formation mechanism of HCHO pollution in the suburban Yangtze River Delta region, China: A box model study and policy implementations

High levels of formaldehyde (HCHO) have been frequently detected during spring-summertime in the densely populated and rapidly developing Yangtze River Delta (YRD) region, China. However, the detailed formation mechanism of HCHO pollution remains unclear. Based on a comprehensive field campaign conducted at Dianshan Lake (DSL) station, a supersite located in the suburban YRD region, the influence of VOCs on HCHO formation, as well as the role of HCHO in the ROx radical recycling was analyzed. Results indicate that the maximum atmospheric oxidation capability (AOC) during HCHO pollution episodes varies from 0.65 × 108 to 1.29 × 108 molecules cm−3 s−1, and high AOC value favors the secondary formation of HCHO. Meanwhile, the photolysis of HCHO accounts for 21.2% of the primary ROx, suggesting the significant role of HCHO in ROx recycling. Isoprene was identified to be a key precursor of HCHO, and the RO from isoprene contributed ∼15% to the total daytime HCHO production rate (PHCHO). Sensitivity analysis reveal that when isoprene, xylene or ethylene was cut off, the simulated HCHO concentration could be reduced by 50%, 15%, or 13%, respectively. Based on the isopleth of HCHO under different VOCs/NOx reduction ratios, we found that the VOCs/NOx reduction ratio should be above 1.03 to mitigate the HCHO pollution. Reactive VOCs (such as isoprene, xylene and alkenes) should be reduced to suppress HCHO pollution in the YRD region.

An Observational Based Modeling of the Surface Layer Particulate Nitrate in the North China Plain During Summertime

AbstractParticulate nitrate (pNO3−) is an important component in atmospheric fine particulate matter. Here, we present a case study investigating the production and loss processes of pNO3− in surface‐layer based on the observation at a regional site Wangdu in North China Plain (NCP) during summer. The averaged diurnal of nitric acid (HNO3) production reached a maximum of 1.5 μg m−3 h−1 determined from the observed OH and NO2, indicating a fast HNO3 production in the surface layer during the daytime. The chemical processes affecting surface nitrate concentration and daily variation were simulated by a box model based on the Regional Atmospheric Chemical Mechanism version 2 and coupled with the ISORROPIA‐II thermodynamic equilibrium model. The chemical formation of total soluble nitrate (TNO3) at the surface layer cannot explain the fast increase of pNO3− in the morning and overshoot pNO3− in the afternoon, suggesting missing processes in the model. The pNO3− budget analysis suggests the importance of entrainment from residual layer air into the surface layer as an important process for surface pNO3− concentration enhancement in the early morning. In the afternoon, the partition to pNO3− was limited due to the high temperature near the ground. Nevertheless, the observed fast nitrate production still significantly overshot pNO3− in the afternoon. This difference indicates HNO3 production was less efficient throughout the boundary layer than what was observed in the surface layer. Our results highlight the importance of vertical measurements to understand the formation mechanism of nitrate pollution in summer.