Clean Period Research Articles

The response of daytime nitrate formation to source emissions reduction based on chemical kinetic and thermodynamic model

Particulate nitrate is an important component of particulate matter and poses a significant threat to the ecosystem and human health. The gas-phase formation pathway of nitrate is extremely important, which mainly comprises the NO2 oxidation process triggered by OH radicals and the nitrate partitioning process. The response of nitrate to source emission reduction during different pollution periods remains unclear. Here, we applied the chemical kinetic and thermodynamics model to explore the importance oxidation process and partitioning process during different pollution periods based on high-time resolution observation data. The result indicated that with the aggravation of pollution, the partitioning process gradually ceases to be a limiting step in the formation of nitrates. The results of the influencing factor analysis indicate that NO2 concentration and aerosol pH values play a more significant role in the formation of nitrates. Specifically, during the clean period, nitrate formation is sensitive to both NO2 concentration and pH values, but during the pollution period, it becomes sensitive only to NO2 concentration. By combining source apportionment, we explored the response of nitrate formation to source emission reduction, and the results showed that the control of vehicle exhaust emissions and coal combustion sources is more effective in mitigating nitrate pollution. Additionally, this study also emphasized the importance of early prevention and control of pollution sources. This research provides scientific evidence for the precise management and control of nitrates.

Pollution Characteristics and Source Apportionment of VOCs in Urban Areas of Shijiazhuang in Spring

Samples of ambient volatile organic compounds （VOCs） were collected using SUMMA canisters at three Country Control Sites in Shijiazhuang during the spring of 2019, 2021, and 2022, which were detected using gas chromatography/mass spectrometry （GC/MS）. To investigate the characteristics and temporal variations of VOCs mass concentration levels, the online monitoring data of ozone （O3） and PM2.5 at the same site were also collected. Subsequently, the ozone formation potential （OFP） and secondary organic aerosol formation potential （SOAFP） were utilized to assess the chemical activity of VOCs. Additionally, the potential source areas of VOCs in spring in Shijiazhuang were further identified using the potential source contribution factor （PSCF） method and concentration weight trajectory analysis （CWT）. Hence, the major VOCs sources were evaluated with the VOCs initial mixing ratio. The results demonstrated that the averaged concentration of VOCs during the polluted period and clean period of spring in Shijiazhuang were 191.17 μg·m-3 and 122.18 μg·m-3, respectively. Meanwhile, the OFP was 361.23 μg·m-3 during the polluted period and 266.96 μg·m-3 during the clean period, whereas the SOAFP was 1.98 μg·m-3 and 1.61 μg·m-3, respectively. Therefore, effective control of benzene, toluene, ethylbenzene, and xylene （BTEX） is crucial for reducing PM2.5 and O3 pollution. Based on the results obtained from weight PSCF and CWT, the potential source areas of VOCs were further identified to be primarily located in the eastern Yuhua District, the high-tech district, and the northern Luancheng District of Shijiazhuang. These areas were influenced not only by local emissions but also by transport from neighboring regions, in which consistency between the CWT and PSCF results further supported these findings. Furthermore, the results obtained from the benzene/toluene/ethylbenzene （B/T/E） and xylene/benzene （X/B） ratios indicated that the main sources of VOCs in Shijiazhuang in spring were vehicle exhaust sources and burning sources, leading to a more serious air mass aging phenomenon. Hence, controlling vehicle emissions and implementing regional cooperative measures are the effective strategies for optimizing the air quality of Shijiazhuang.

Response of PM2.5 chemical composition to the emission reduction and meteorological variation during the COVID-19 lockdown

PM2.5 is a main atmospheric pollutant with various sources and complex chemical compositions, which are influenced by various factors, such as anthropogenic emissions (AE) and meteorological conditions (MC). MC have a significant impacts on variations in atmospheric pollutant; therefore, emission reduction policies and ambient air quality are non-linearly correlated, which hinders the accurate assessment of the effectiveness of control measures. In this study, we conducted online observations of PM2.5 and its chemical composition in Hohhot, China, from December 1, 2019, to February 29, 2020, to investigate how the chemical compositions of PM2.5 respond to the variations in AE and MC. Moreover, the random forest (RF) model was used to quantify the contributions of AE and MC to PM2.5 and its chemical composition during severe hazes and the COVID-19 pandemic lockdown period. During the clean period, MC reduced PM2.5 concentrations by 124%, while MC incresed PM2.5 concentrations by 49% during severe pollution episode. Inorganic aerosols (SO42−, NO3−, and NH4+) showed the strongest response to MC. MC significantly contributed to PM2.5 (36%), SO42− (32%), NO3− (29%), NH4+ (28%), OC (22%), and SOC (17%) levels during pollution episodes. From the pre-lockdown to lockdown period, AE (MC) contributed 52% (48%), 81% (19%), 48% (52%), 68% (32%), 59% (41%), and 288% (−188%) to the PM2.5, SO42−, NO3−, NH4+, OC, and SOC reductions, respectively. The variations in MC (especially the increase in relative humidity) rapidly generated meteorologically sensitive species (SO42−, NO3−, and NH4+), which led to severe winter pollution. This study provides a reference for assessing the net benefits of emission reduction measures for PM2.5 and its chemical compositions.

Characteristics and Source Analysis of Volatile Organic Compounds in Typical Ozone Pollution Processes During Summer in Jinan, China

Based on a typical ozone （O3） pollution process in Jinan City from June 16 to 26, 2021, the variation characteristics of O3 and its precursor volatile organic compounds （VOCs） during different pollution periods （clean period （CP）, pollution rise period （PRP）, heavy pollution period （HPP）, and pollution decline period （PDP）） in the urban area were analyzed. Both positive matrix factorization （PMF） and an observation-based model （OBM） were used to identify the main sources of VOCs, O3 production mechanisms, and sensitive species. The results showed that the average value of ρ（O3-8h） during the HPP period in the urban area was （246.67±11.24） μg·m-3, and ρ（O3-1h） had a peak value of 300 μg·m-3. The volume fractions of VOCs and NO2 concentration were affected by the decrease in planetary boundary layer and wind speed, which were 76.99%-145.36% and 127.78%-141.18% higher than those in the other three periods, respectively, and were the main reasons for the aggravation of O3 pollution. Alkanes, oxygenated volatile organic compounds （OVOCs）, and halogenated hydrocarbons accounted for 43.81%, 20.98%, and 17.43% of VOCs in urban areas, respectively. All of them showed significant growth during the HPP period, with acetone, propane, and ethane being the top three species by volume in each stage and isopentane showing the highest growth during the HPP period. Alkene, alkanes, and aromatic hydrocarbons accounted for 40.19%, 28.06%, and 21.92% of the ozone generation potential （OFP）. 1-butene, toluene, isopentane, and isoprene were the species with higher OFP. Isoprene had the highest OFP during the PRP phase, and 1-butene had the highest OFP during the HPP phase. The volume fraction of isopentane significantly increased OFP. The correlation coefficient between VOCs and CO preliminarily indicated that motor vehicle exhaust and oil and gas volatilization were the main sources of VOCs during the HPP period. Further use of PMF revealed that solvent use sources, combustion sources, motor vehicle exhaust+oil and gas volatilization sources, industrial emission sources, and plant sources were important sources of VOCs in urban areas. The contribution of motor vehicle exhaust+oil and gas volatilization sources in the HPP period to VOCs was 3.09-14.72 times higher than that in other periods. The contribution of solvent use sources to VOCs was approximately 2.50 times higher than that in the CP and PRP periods. The main sources of VOCs volume fraction increase were motor vehicle exhaust, oil and gas volatilization sources, and solvent use sources. Potential sources and concentration weight analysis found that VOCs were also affected by the transmission of VOCs to Binzhou and Dongying in the northeast direction. The OBM results indicated that the main pathway of O3 formation in urban areas was the reaction of peroxide hydroxyl radicals （HO2·） and methyl peroxide radicals （CH3O2·） with NO, and the net ozone generation rate during the HPP phase [P（O3）net] was 24×10-9 h-1. Based on the sensitivity experiment results, the alkene components of 1-butene, propylene, cis-2-butene, and ethylene were the dominant species for O3 production.

Source apportionment and wet scavenging ability of atmospheric black carbon during haze in Northeast China

Seasonal variations in black carbon (BC) pollution characteristics during haze episodes in Benxi city, Liaoning province, were analyzed using year-long measurements of BC, carbon monoxide (CO), and PM2.5. Haze frequencies were recorded to be 0.07, 0.03 and 0.14 in spring, autumn, and winter respectively. Solid fuel contributions increased notably by 7%–8% during haze events compared to clean periods in all seasons. Transitioning from clean to haze periods led to ΔBC/ΔCO increases of 16% in spring and autumn, and 6.8% in winter, while BC/PM2.5 ratios decreased by approximately 33%, 50%, and 24% for spring, autumn, and winter respectively, likely indicating enhanced residential and industrial contributions. These further led to an increase in BC absorption capacities by factors of around 2.2 in spring and autumn, and up to 2.6 in winter during haze periods. Despite liquid fuel sources dominating BC emissions, certain haze episodes (frequency <10%) showed solid fuel contributions of up to 65%, highlighting BC pollution complexity in the region during haze. Backward trajectories analysis revealed local air masses from Liaoning province arrived consistently with the most occurrence of haze events across all seasons, while long-range air masses from Mongolian regions, though with less frequent occurrence during haze periods, significantly elevated BC loadings from solid fuel sources, particularly in spring and autumn due to biomass burning. Despite higher BC wet scavenging rates (WSR) in long-range air masses (0.072 ng m−3 ppbv−1 mm−1) compared to local air masses (0.039 ng m−3 ppbv−1 mm−1), significant BC transport persisted due to limited precipitation along transport pathways, especially during haze periods. These findings provide crucial insights for policymakers, highlighting the need for targeted haze prevention and control strategies focusing on mitigating BC emissions in Northeast China.

Using sulfur isotopes to constrain the sources of sulfate in PM2.5 during the winter in Jiaozuo City

Sulfate (SO42−) is one of the main driving forces behind the explosive growth of atmospheric fine particulate matter (PM2.5), and it scatters sunlight, contributing to atmospheric cooling. Investigating the sources and transformation of SO42− is crucial for understanding PM2.5 pollution and its implications for climate change. Despite a continuous decline in PM2.5 concentrations in China since 2015, it remains unclear whether there have been changes in the sources and transformation processes of SO42−. Furthermore, previous studies that utilized isotope techniques for source identification have often overlooked the impact of isotope fractionation. This study focuses on atmospheric PM2.5 in Jiaozuo based on samples collected from December 2017 to February 2018. The analysis encompassed both the water-soluble ions and sulfur isotope compositions of SO42− (δ34S–SO42−). By employing a Bayesian isotope mixing model, quantitative analysis of SO42− sources in winter atmospheric PM2.5 in the study area was conducted. The findings revealed that the δ34S–SO42− values of winter PM2.5 ranged from −0.1‰ to 9.8‰, with an arithmetic mean of 4.9 ± 1.5‰ (n = 74). After considering sulfur isotope fractionation effects and the impact of primary SO42−, the calculated results suggested that on average, the contributions of primary SO42−, coal combustion, vehicle exhaust, biomass burning, and oil combustion to the SO42− in winter PM2.5 were 24.9 ± 15.7%, 41.2 ± 2.6%, 27.9 ± 5.3%, 4.8 ± 3.7%, and 1.2 ± 0.7%, respectively. Compared with the clean period, the contribution of the primary SO42− decreased significantly during haze episodes, while the contribution of the secondary SO42− increased. The contribution of coal combustion to the secondary SO42− increased notably by 21.9%, while the contributions from other secondary sulfate remained relatively stable. The lower δ34S values of the atmospheric PM2.5 in Jiaozuo affirm the significant impact of the anthropogenic SO2 input on the sulfur isotope composition of the atmospheric sulfate. Analysis confirmed that the decrease in the contribution of coal combustion to atmospheric SO42− in the study area, indicating the positive effects of regional air pollution control measures. Nevertheless, continued attention should be paid to the influences of coal combustion and vehicle exhaust on regional air pollution.

Influence of ozone pollution on the mixing state and formation of oxygenated organics containing single particles

The formation and aging processes of oxygenated organic molecules (OOMs) are important for understanding the formation mechanisms of secondary organic aerosols (SOAs) in the field. In this study, we investigated the mixing states of OOM particles by identifying several oxygenated species along with the distributions of secondary organic carbon (SOC) during both clean and ozone (O3)-polluted periods in July and September of 2022 in Guangzhou, China. OOM-containing particles accounted for 57 % and 49 % of the total detected single particles in July and September, respectively. Most of the OOM particles were internally mixed with sulfate and nitrate, while elemental carbon and hydrocarbon species were absent. Despite the higher SOC/OC ratio in September (81 %) than it in July (72 %), comparative investigations of the mass spectra, diurnal patterns, and distributions of OOM particles revealed the same composition and aging states of OOMs in two O3 pollution periods. As the O3 concentration increased from the clean to the polluted periods, the ratio of SOC to OC increased along with the relative abundance of secondary OOM particles among total OOM particles. In contrast, the relative abundance of OC-type OOM particles gradually decreased, indicating the conversion of hydrocarbon species into OOMs as the SOC/OC ratio increased. Both the bulk analysis of SOC from filter measurement and the mixing states of OOM particles suggested that OOM production and degree of oxidation were higher in the O3-polluted periods than in the clean periods. These results elucidate the effects of O3 pollution on the OOM formation process and offer new perspectives for the joint investigation of SOA production based on filter sampling and single-particle measurements.

Exploring the role of aerosol-ozone interactions on O3 surge and PM2.5 decline during the clean air action period in Eastern China 2014–2020

The China implemented the Clean Air Action Plan (CAAP) in September 2013 to address the pressing air pollution problem. This initiative yielded a noteworthy reduction in PM2.5 while simultaneously witnessing the O3 elevation. Here, we used a revised WRF-Chem model to study the drivers (anthropogenic emissions (EMI), meteorological changes (MET)) of decreasing PM2.5 and increasing O3 in eastern China across the four seasons from 2014 to 2020, focusing on the response of aerosol-ozone interaction (AOI) to emission reduction (AOI_ER). In contrast to the original version, the model provided more comprehensive feedback of aerosols on O3, including radiation effects and heterogeneous chemistry. Our survey showed that EMI was the main factor causing the PM2.5 decline and O3 increase. The influence of MET on both O3 and PM2.5 exhibited seasonal variations. Compared to 2014, emission reduction during CAAP weakened the inhibition of aerosol radiative effect on meteorological parameters and photolysis rate, causing a rise in surface shortwave radiation (SW), temperature (T2), planetary boundary layer height (PBLH), wind speed (WS10), JNO2, and JO1D throughout the CAAP period. This increased the O3 by 0.57–2.11 ppb in the four seasons and enhanced the emission-reduction-induced O3 increase by 22.2%–57.3%. Emission reduction alleviated the summer negative feedback of AOI on PM2.5, increasing by 4.61 μg m−3, thereby offsetting the 16.7% emission reduction efficacy. Oppositely, in spring, autumn, and winter, emission reduction weakened the promotion of AOI on PM2.5, resulting in a decrease by 2.5–3.12 μg m−3, amplified the emission-reduction-induced PM2.5 reduction by 8.3%–26.6%. Nitrate and sulfate aerosols generated by heterogeneous chemistry emerged as the primary components driving the alterations in PM2.5 within the context of emission reduction. Our research emphasized the importance of considering changes in AOI when formulating emission control policies and evaluating their effectiveness. More effective emission policies should focus on comprehensively considering the emissions and the weakened aerosol effects to achieve better air quality and health benefits.

Optimum dynamic dispatch of clean water, methane, electricity and heat considering carbon capture

This paper suggests a novel clean water, natural gas, heat and power generation system using wind turbine generators, PVT panels, bioenergy power plants, micro-hydro power plants, micro-cogeneration units (MCUs), battery energy storage system, thermal energy storage system and plug-in electric vehicles (PEVs). In this system, a power to gas technology consisting of a carbon capture unit, an electrolyzer, a hydrogen storage unit, and a methanation process, is used to supply the natural gas demand using CO2 captured from the MCUs and the hydrogen generated by the clean water electrolyzer. Furthermore, the electricity is consumed by a desalination unit to procure the clean water demand, carbon captured unit (CCU), electrolyzer water inflow, and fill up the water storage tank. At peak clean water demand periods, the excess water is pumped from the storage tank to the consumption side. Demand response program (DRP) is used for levelling the demand. Here, total cost for water-gas-heat-power nexus model throughout the day with and without DRP for three different scenarios is minimized by using quasi-oppositional fast convergence evolutionary programming, fast convergence evolutionary programming, self-organizing hierarchical particle swarm optimizer with time-varying acceleration coefficients and differential evolution. It is seen from numerical results that cost attained with DRP is less than the cost attained without DRP.

Topology Learning in Radial Dynamical Systems With Unreliable Data

Many complex engineering systems admit bidirectional and linear couplings between their agents. Blind and passive methods to identify such influence pathways/couplings from data are central to many applications. However, dynamically related data-streams originating at different sources are prone to corruption caused by asynchronous time-stamps of different streams, packet drops and noise. Such imperfect information may be present in the entire observation period, and hence not detected by change-detection algorithms that require an initial clean observation period. In this article, we provide a novel approach to detect the location of corrupt agents as well as present an algorithm to learn the structure of radial dynamical systems despite corrupted data streams. In particular, we show that our approach provably learns the true radial structure if the unknown corrupted nodes are at least three <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hops</i> away from each other. Our theoretical results are further validated in a test dynamical network.

Effects of aerosol water content and acidity on the light absorption of atmospheric humic-like substances in winter

Atmospheric humic-like substances (HULIS) could affect regional climate due to their strong light-absorbing capacity. Daily fine particulate matter (PM2.5) samples were collected from December 18, 2016 to January 8, 2017 at an urban site in Chongqing, Southwest China. The mean concentration of HULIS in terms of carbon (HULIS-C) was 6.4 ± 3.4 μg m−3, accounting for 72% of water-soluble organic carbon. The mass absorption efficiency at 365 nm (MAE365) and absorption Ångström index (AAE) of atmospheric HULIS were 2.8 ± 0.30 m2 g−1 C and 4.6 ± 0.37, respectively. Good correlations between the light absorption coefficients of HULIS at 365 nm (Abs365) and the concentrations of K+, elemental carbon, NO3−, and NH4+ were observed, with correlation coefficients higher than 0.83, indicating that biomass burning and secondary formation were potential sources of light-absorbing HULIS, as evidenced by abundant fluorescent components related to less-oxygenated HULIS. Comparing the changes in Abs365 values, concentrations of major water-soluble inorganic ions and carbonaceous compounds in PM2.5, and environmental factors during the clean and pollution periods, we found that extensive biomass burning during the pollution period contributed significantly to the increase of Abs365 values. Moreover, the aerosol pH during the pollution period was close to 4, and NO2 concentration and aerosol water content were about 1.6 and 2.7 times higher than those during the clean period, respectively, which were favorable to form secondary HULIS through aqueous phase reactions in the presence of high NOx, resulting in an evident increase in its light absorption. Knowledge generated from this study is critical for evaluating the regional radiative forcing of brown carbon in southwest China.

Simulation of the Working Volume Reduction through the Bioconversion Model (BioModel) and Its Validation Using Biogas Plant Data for the Prediction of the Optimal Reactor Cleaning Period

The present study focuses on the working volume reduction of anaerobic reactors in biogas plants, which is caused by inorganic material accumulation and inadequate mixing and affects methane production and plant profitability. Precipitation phenomena lead to periodic reactor cleaning processes, which complicate the operation of the plant and increase its operating costs. For this purpose, the bioconversion model (BioModel) was utilized by modifying its conditions to accurately simulate the reduction of the working volume of a biogas plant facing precipitation problems for a study period of 150 days. The modified BioModel exhibited notable results in the prediction of methane production, with an average deviation of 1.97% from the plant’s data. After validation, based on the model results, an equation was set up to predict the optimal reactor cleaning period. Incidentally, the optimal cleaning time was calculated at 5.1 years, which is very close to the period during which the cleaning of the reactors of the studied biogas plant took place (5.5 years). The findings of this research showed that the modified BioModel, along with the developed equation, can be effectively used as a tool for the prediction of the optimal reactor cleaning period.

Growth of nitrate contribution to aerosol pollution during wintertime in Xi'an, northwest China: Formation mechanism and effects of NH3

With the strengthened controls on SO2 emissions and extensive increases in motor vehicles’ exhaust, aerosol pollution shifts from sulfate-rich to nitrate-rich in recent years in Xi'an, China. To further gain insights into the factors on nitrate formation and efficiently mitigate air pollution, highly time-resolved observations of water-soluble inorganic ions (WSIIs) in PM2.5 were measured in a suburban area of Xi'an, China during wintertime. Hourly concentration of total WSIIs is 39.8 μg m−3 on average, accounting for 50.3% of PM2.5 mass. In contrast to a slight decrease in the mass fraction of SO42−, NO3− shows a significant increase of the PM2.5 contribution with the aggravation of aerosol pollution. This suggests the importance of NO3− formation to haze evolution. Furthermore, homogeneous reactions govern the formation of NO3−, while alkali metals such as calcium and sodium play an additional role in retaining NO3− in PM2.5 during clean periods. However, the heterogeneous hydrolysis reaction contributed more to NO3− formation during the pollution periods under high relative humidity. Our investigation reveals that temperature, relative humidity, oxidant, and ammonia emissions facilitate rapid NO3− formation. Using the random forest (RF) model, NO3− concentrations were successfully simulated with measured variables for the training and testing datasets (R2 > 0.95). Among these variables, CO, NH3, and NO2 were found to be the main factors affecting the NO3− concentrations. Compared with the period without vehicle restriction, the contributions of NO3− and NH4+ to PM2.5 mass decreased by 5.3% and 3.4% in traffic restriction periods, respectively. The vehicle restriction leads to the decreases of precursor gases of NO2, SO2, and NH3 by 12.8%, 5.9%, and 27.6%, respectively. The results demonstrate collaborative emission reduction of NOx and NH3 by vehicle restrictions, and using new energy vehicles (or electric vehicles) can effectively alleviate particulate matter pollution in northwest China.

Health Care Costs Following COVID-19 Hospitalization Prior to Vaccine Availability.

Postacute sequelae of coronavirus (PASC) disease of 2019 (COVID-19) include morbidity and mortality, but little is known of the impact on medical expenditures. This study measures patients' health care costs after COVID hospitalization before vaccinations. The Merative MarketScan database is used to track trends in medical expenditures for commercially insured patients hospitalized for COVID-19 (case subjects) compared with COVID-19 patients not hospitalized (control subjects) using a propensity score matching model. Medical expenditures were estimated from 30-, 60-, and 120-day clean periods after an initial COVID-19 encounter through the end of 2020. Average total medical expenditures were 96% higher for individuals hospitalized for COVID-19 starting 30 days after initial COVID-19 encounter and almost 70% higher 120 days after based on the propensity score matching. The average spending differential was $11,242 30 days after and $4959 120 days after. This effect is highest for inpatient admissions and services 60 days after at $56,862 and lowest among pharmaceuticals 120 days after at $329. The magnitude of the difference is greater for those with hypertension or diabetes where total expenditures is $14,958 30 days after, and $5962 120 days after compared with those without these chronic conditions. The results suggest both health and economic implications for COVID-19 hospitalization and supports the use of vaccinations to help mitigate these implications. PASC includes increased health care costs for hospitalized patients, particularly for those with chronic conditions. Preventing COVID-19 hospitalization has economic value in terms of reduced medical spending in addition to health benefits associated with reduced morbidity and mortality.

A comprehensive observation on the pollution characteristics of peroxyacetyl nitrate (PAN) in Beijing, China

Peroxyacetyl nitrate (PAN) is a typical secondary photochemical product in the atmospheric environment with significant adverse effects on human health and plant growth. In this study, PAN and other pollutants, as well as meteorological conditions were observed intensively from August to September in 2022 at a typical urban sampling site in Beijing, China. The mean and maximum PAN concentrations during the observation period were 1.00 ± 0.97 ppb and 4.84 ppb, respectively. Severe photochemical pollution occurred during the observation period, with the mean PAN concentration about 3.1 times higher than that during the clean period. There was a good positive correlation between O3 and PAN, and their correlation was higher during the O3 exposure period than that during the clean period. The simulated results by box-model coupled with the Master Chemical Mechanism (MCM v3.3.1) showed that the O3-related reactions were the largest sources of OH radicals during O3 exposure period, which was conducive to the co-contamination of PAN and O3. Acetaldehyde (CH3CHO) and methylglyoxal (MGLY) were the largest OVOCs precursors of peroxyacetyl radicals (PA), with the contributions to the total PA generated by OVOCs about 67 % – 83 % and 17 % – 30 %, respectively. The reduction of emissions from liquefied petroleum gas (LPG) and solvent usage has the highest reduction effect on PAN and O3, followed by the control of gasoline vehicle exhaust emissions. This study deepens the understanding of the PAN photochemistry in urban areas with high O3 background conditions and the impact of anthropogenic activities on the photochemical pollution. Meanwhile, the findings of this study highlight the necessity of strengthening anthropogenic emissions control to effectively reduce the co-contamination of PAN and O3 in Beijing in the future.

Primary sources of HONO vary during the daytime: Insights based on a field campaign

Nitrous acid (HONO) is an established precursor of hydroxyl (OH) radical and has significant impacts on the formation of PM2.5 and O3. Despite extensive research on HONO observation in recent years, knowledge regarding its sources and sinks in urban areas remains inadequate. In this study, we monitored the atmospheric concentrations of HONO and related pollutants, including gaseous nitric acid and particulate nitrate, simultaneously at a supersite in downtown Chengdu, a megacity in southwestern China during spring, when was chosen due to its tolerance for both PM2.5 and O3 pollution. Furthermore, we employed the random forest model to fill the missing data of HONO, which exhibited good predictive performance (R2 = 0.96, RMSE = 0.36 ppbv). During this campaign, the average mixing ratio of HONO was measured to be 1.0 ± 0.7 ppbv. Notably, during periods of high O3 and PM2.5 concentrations, the mixing ratio of HONO was >50 % higher compared to the clean period. We developed a comprehensive parameterization scheme for the HONO budget, and it performed well in simulating diurnal variations of HONO. Based on the HONO budget analysis, we identified different mechanisms that dominate HONO formation at different times of the day. Vehicle emissions and NO2 heterogeneous conversions were found to be the primary sources of HONO during nighttime (21.0 %, 30.2 %, respectively, from 18:00 to 7:00 the next day). In the morning (7:00–12:00), NO2 heterogeneous conversions and the reaction of NO with OH became the main sources (35.0 %, 32.2 %, respectively). However, in the afternoon (12:00–18:00), the heterogeneous photolysis of HNO3 on PM2.5 was identified as the most substantial source of HONO (contributing 52.5 %). This study highlights the significant variations in primary HONO sources throughout the day.

On Carbon Tax Effectiveness in Inducing a Clean Technology Transition: An Evaluation Based on Optimal Strategic Capacity Planning

This paper studies carbon tax effectiveness in inducing a transition to cleaner production when a firm faces different technologies and demands over a planning horizon. To determine carbon tax effectiveness, we propose a model based on strategic capacity production planning under carbon taxes that considers proper performance measures. The model, which is formulated as a mixed integer linear problem (MILP), considers issues that previous works have not studied jointly, and that are relevant in a technological transition, such as machine replacement, workforce planning, and maintenance. The effectiveness measures consider levels of clean production and periods to reach a technological transition. Our computational experiments, based on a real case, have shown that in the absence of carbon taxes, a firm has no incentive to transition to clean technology. Still, the effectiveness of carbon taxes depends on the characteristics of the technology available for the production process and the magnitude of the demand. We include managerial insights aimed at both companies and the environmental authority.

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.

Formation mechanism, precursor sensitivity and control strategies of summertime ozone on the Fenwei Plain, China

As one of the most polluted regions in China, the Fenwei Plain has suffered severe summertime ozone (O3) pollution in recent years. However, related studies in this region are still scarce. In this study, a comprehensive observation campaign was conducted in a typical city on the Fenwei Plain. An observation-based model (OBM) was used to investigate the summer O3 formation mechanism, precursor sensitivity and control strategies during O3-polluted and clean periods. Our results showed that O3 pollution was accompanied by increased O3 precursor concentrations (∼15% higher) and unfavorable meteorological conditions. In situ O3 production played a dominant role in the daytime O3 concentration increment in both polluted (+6.0 ppbv/h) and clean (+3.5 ppbv/h) periods. HO2 + NO (65.9%–66.7%) was the most dominant pathway of daytime O3 formation, and OH + NO2 (41.3%–63.1%) was the most dominant pathway of O3 destruction. Regional transport has a certain contribution to the occurrence of polluted days, as well as a diluting effect on clean days. Regional transport had a certain contribution effect on polluted days and a dilution effect on clean days. The southeastern regions were potential source regions of high O3, and the northwestern regions were potential source regions of low O3. When pollution occurred, the O3 formation control regimes transformed from a volatile organic compound (VOC)-limited regime to a transition regime, corresponding to an increase in precursor concentrations and stronger local O3 production. A 30% reduction in VOCs and a 20% reduction in NOx (VOCs/NOx ≈ 1.5) were determined to be the optimal control strategies to achieve the O3 control target (82 ppbv) in summer. VOC reductions should target reactive and O3-sensitive species (Oxygened VOCs, alkenes, aromatics) to effectively alleviate O3 pollution. This study could provide scientific support for local O3 pollution control on the Fenwei Plain.

Molecular Distributions and 13C Isotopic Composition of Dicarboxylic Acids, Oxocarboxylic Acids, and α‐dicarbonyls in Wintertime PM2.5 at Three Sites Over Northeast Asia: Implications for Origins and Long‐Range Atmospheric Transport

AbstractTo investigate the spatial changes in origins and impact of long‐range transported air masses on organic aerosols (OA) loading and composition over Northeast Asia, fine aerosols (PM2.5) were collected at three sites: Tianjin (TJ), North China and in Padori (PD), and Daejeon (DJ), South Korea, during winter 2019. We studied molecular distributions and compound‐specific stable carbon isotopic composition (δ13C) of dicarboxylic acids, oxocarboxylic acids and α‐dicarbonyls, and carbonaceous and inorganic ionic components in PM2.5. Concentrations of organic carbon was drastically enhanced in haze period compared to that in clean period, but elemental carbon was almost comparable between the two periods. Concentrations of total diacids, oxoacids, and α‐dicarbonyls were higher at TJ followed by DJ and PD during haze period and at DJ followed by TJ and PD during clean period. On average, oxalic acid (C2) was the most abundant among measured species at all three sites, followed by methyl glyoxal (MeGly) and glyoxylic acid (ωC2) at TJ and DJ, and succinic acid (C4) and ωC2 were almost equal and second most abundant followed by MeGly at PD. Based on the mass ratios and linear relations of selected species together with δ13C of diacids and related compounds, we found that contributions of OA from biomass burning/biogenic emissions and their aging were higher at TJ and PD, whereas at DJ, emissions from anthropogenic sources and in situ secondary formation were also important. Furthermore, this study implies that long‐range atmospheric transport of aerosols from source regions to downwind regions are substantial over Northeast Asia.