Ozone Production Research Articles

Measurement and Risk Analysis of Ozone (O3) Concentrations in the 9 MeV and 12 MeV Electron Mode LINAC

This study investigates potential non-radiation hazards, specifically Ozone (O3) production, during Linear Accelerator (LINAC) electron mode radiotherapy. The research uses experimental measurements to determine Ozone concentration in the LINAC patient waiting room and control room. Measurements are taken assuming a ±2-hour delay in one working day, using 9 MeV and 12 MeV energy, 400 MU dose rate, and illumination angles of 0o, 90o, and 270o. Maximum Ozone concentrations in the LINAC patient waiting room and control room are found to be 6.6 ppb (12 MeV) and 8.3 ppb (12 MeV), respectively. These concentrations fall below the chemical threshold limit and are deemed safe for human exposure. Notably, potentially detectable Ozone levels are observed in the LINAC banker. Overall, this research highlights the importance of monitoring Ozone levels to ensure the safety of both patients and personnel in LINAC facilities.

Exploring ozone production sensitivity to NOx and VOCs in the New York City airshed in the spring and summers of 2017–2019

Reducing ozone in the New York City (NYC) region requires understanding the nonlinearity of ozone production (PO3) and its sensitivity to volatile organic compounds (VOCs) and nitrogen oxides (NOx = NO2 + NO). Using observations from the Long Island Sound Tropospheric Ozone Study (LISTOS) in the late spring and summers of 2017–2019 and a 0-D box model, we test the sensitivity of PO3 to ozone precursors. PO3 is greater in the morning than the afternoon due to increased concentrations of NO2 and VOC. This diurnal variation in PO3 is enhanced in the late summer. Based on the model response of PO3 to changes in initial NO2, 14% of samples are within a VOC-limited regime. The metric LROx/LNOx, which compares the radical loss rates via self-reaction to their reaction with NO2, indicates an additional 17% of samples are in transition between NOx and VOC-limited regimes (0.30 <= LROx/LNOx <= 1). We often find PO3 to be VOC-limited in NYC and along the Connecticut coastline (I-95 corridor). In these samples, PO3 is most sensitive to isoprene, propene, and isopentane, and individual VOCs have strong diurnal and seasonal variations. We further compare PO3 calculations using the near explicit Master Chemical Mechanism (MCMv3.3.1) and Carbon Bond 6 revision 2 (CB6r2) for a more direct link to regulatory air quality models. Modeled PO3 is 20% greater in MCMv3.3.1, due largely to the speciation of VOC and organic peroxy radicals, however the bounds of LROx/LNOx used to determine the transition range between PO3 regimes remain the same.

Comparison of Ozone Production in Planar DBD of Different Modes

Comparison of Ozone Production in Planar DBD of Different Modes

Characteristics，Sources，and Ozone-sensitive Species of VOCs in Four Seasons in Yuncheng

Based on the one-year observational data of volatile organic compounds （VOCs） in an urban area of Yuncheng in 2021， the concentration， composition， sources， and ozone-sensitive species of VOCs in four seasons were analyzed. The results showed that the average annual concentration of VOCs was （32.1 ±24.2）×10-9， i.e.， at the national middle level. The seasonal concentrations of VOCs were in the order of： winter （46.3×10-9）&gt; autumn （35.5×10-9）&gt; spring （25.6×10-9）&gt; summer （21.2×10-9）. Alkanes and OVOCs were the most dominant VOCs compounds， accounting for 69.0%-80.4% of TVOCs in Yuncheng. Affected by changes in source emissions， the proportion of OVOCs was higher in spring and summer （41%-43%）， whereas the proportion of alkanes was higher in autumn and winter （42%-43%）. Vehicle exhaust， LPG/NG， industrial production， and combustion sources were identified as the main sources of VOCs in Yuncheng. The largest contributors in the four seasons were vehicle exhaust （28.5% in spring）， secondary + combustion sources （29.0% in summer）， LPG/NG sources （30.4% in autumn）， and coal combustion （27.3% in winter）. The ozone formation was located in the transitional regime in summer and in the VOC-limited regime in other seasons. Ozone production was more sensitive to alkenes （isoprene， ethylene， and propene）， OVOCs （acetaldehyde and propanal）， and aromatics （xylene， toluene， and benzene）. Winter was more sensitive to ethylene， and the other seasons were more sensitive to isoprene. The primary emission sources related to these sensitive species should be reduced to achieve the goal of air quality improvement.

Intensive photochemical oxidation in the marine atmosphere: evidence from direct radical measurements

Abstract. Comprehensive observations of hydroxyl (OH) and hydroperoxy (HO2) radicals were conducted in October 2019 at a coastal continental site in the Pearl River Delta (YMK site, 22.55∘ N, 114.60∘ E). The daily maximum OH and HO2 concentrations were (4.7–9.5) × 106 and (4.2–8.1) × 108 cm−3, respectively. The synchronized air mass transport from the northern cities and the South China Sea exerted a time-varying influence on atmospheric oxidation. Under a typical ocean-atmosphere (OCM), reasonable measurement model agreement was achieved for both OH and HO2 using a 0-D chemical box model incorporating the regional atmospheric chemistry mechanism version 2-Leuven isoprene mechanism (RACM2-LIM1), with daily averages of 4.5 × 106 and 4.9 × 108 cm−3, respectively. Land mass (LAM) influence promoted more active photochemical processes, with daily averages of 7.1 × 106 and 5.2 × 108 cm−3 for OH and HO2, respectively. Heterogeneous uptake had certain effects on HOx chemistry, but the influence of the halogen mechanism was limited by NOx level. Intensive photochemistry occurred after precursor accumulation, allowing local net ozone production comparable with surrounding suburban environments (5.52 ppb h−1 during the LAM period). The rapid oxidation process was accompanied by a higher diurnal nitrous acid (HONO) concentration (&gt; 400 ppt). After a sensitivity test, HONO-related chemistry elevated the ozone production rate by 33 % and 39 % during the LAM and OCM periods, respectively. The nitric acid (P(HNO3)) and sulfuric acid (P(H2SO4)) formation rates also increased simultaneously (∼ 43 % and ∼ 48 % for LAM and OCM sectors, respectively). In the ozone-prediction test, simulated O3 decreased from ∼ 75 ppb to a global background (∼ 35 ppb) without the HONO constraint, and daytime HONO concentrations were reduced to a low level (∼ 70 ppt). For coastal cities, the particularity of the HONO chemistry tends to influence the ozone-sensitive system and eventually magnifies the background ozone. Therefore, the promotion of oxidation by elevated precursors deserves a lot of attention when aiding pollution mitigation policies.

Synergistic promotion by highly active square-shaped lead oxide and visualized electrolyzer for enhanced electrochemical ozone production

Electrochemical ozone production (EOP) is an intrinsically safe technology compared to Corona discharge methods for ozone generation. However, EOP technology exhibits higher electrical utility demand. Herein, a square-shaped lead oxide (PbOx-CTAB-120) electrocatalyst with outstanding EOP activity has been successfully prepared by a simple method. Then the PbOx-CTAB-120 was assembled into a newly visualized EOP electrolyzer (with parallel flow field) at 1.0 A cm−2 in ultrapure water. The gaseous ozone yield reached 588 mg h−1 g−1catalyst, corresponding to a specific energy consumption (PEOP) of 56 Wh g−1gaseous ozone. In-situ18O isotope-labelled differential electrochemical mass spectrometry reveals that PbOx-CTAB-120 undergoes phase shuttling to β-PbO2via the lattice oxygen oxidation mechanism pathway. Furthermore, density functional theory calculations for multiple reaction pathways on the Pb3O4 (110) surface also demonstrated the participance of lattice oxygen in the EOP process, with the results show that the oxygen vacancy generated from lattice oxygen migration could effectively stabilize the OOH* and O2* reaction intermediate in contrast to the adsorbate evolution mechanism. Therefore, the presence of highly stabilized surfaces Pb3O4 (110) on PbOx-CTAB-120 before phase shuttling and the stabilization of β-PbO2 (101) and β-PbO2 (110) crystalline surfaces after phase shuttling allowed PbOx-CTAB-120 to maintain its excellent EOP activity and stability. Moreover, based on computational fluid dynamics simulations and experimental observations, the parallel flow field design facilitated efficient mass transfer of the gaseous product (O2+O3) and effective thermal dissipation of the system. In addition, the high activity electrocatalyst coupled with the optimized EOP electrolyzer enabled efficient in-situ degradation of organic species.

Enhancing ozone nowcasting over East Asia using a data-to-data translation approach with observations from a geostationary environment monitoring spectrometer

The degradation of air quality caused by excessive anthropogenic ozone (O3) concentrations negatively affects ecosystems and the atmosphere. To monitor this issue, the Geostationary Environment Monitoring Spectrometer (GEMS) aboard the Geostationary Korea Multi-Purpose Satellite (GK)-2B provides ozone products over Asia-centered circular regions based on the ozone algorithm derived from representative polar-orbit atmospheric environmental satellites. In this study, we developed a few-hour GEMS O3 nowcasting model using data-to-data (D2D) translation with a conditional generative adversarial network. This model is based on hourly GEMS O3 time-series products and can be used to predict ozone concentrations. The D2D model underwent training and testing employing paired input and output datasets of GEMS O3, with data collected from March 22, 2020, to June 21, 2020, and from March 22, 2021, to June 18, 2021, respectively. The resulting D2D ozone nowcasting model was used to determine ozone concentrations in time zones where GEMS O3 products were unavailable. Test results of the D2D model demonstrated excellent statistical scores, including a bias of 2.162 Dobson Units (DU, where 1 DU corresponds to 2.687 × 1016 molecules/cm2), root-mean-square error (RMSE) of 5.606 DU, a correlation coefficient (CC) of 0.994 for 1-h prediction, a bias of 1.421 DU, RMSE of 5.903 DU, and CC of 0.992 for 2-h prediction, and a bias of 1.169 DU, RMSE of 6.797 DU, and CC of 0.988 for 3-h prediction. Despite the dataset pairing and number limitations, the D2D prediction model accurately forecasted GEMS O3 within 3 h in East Asia.

High Selectivity toward Electrochemical Ozone Production of Sb‐SnO2 with Cu and Ni Co‐doped

AbstractNi‐Sb‐SnO2(Ni‐ATO) can generate ozone electrochemically which compensates the energy efficiency. However, the selectivity of electrochemical ozone production (EOP) on Ni‐ATO surface is yet insufficient for practical application. In this study, ATO with Cu and Ni co‐doped (CuNi‐ATO) is prepared to enhance the electrochemical performance and stability of ozone generation. CuNi‐ATO achieves the highest known current efficiency of 71% for EOP under acidic conditions, which is 2.4 times higher than that of Ni‐ATO. Efficient EOP is maintained with diverse pH, temperature, and electrolytes. Notably, the service lifetime of CuNi‐ATO is 2.7 times longer than that of Ni‐ATO. DFT calculations further reveal that ATO with Cu and Ni co‐doped presents weakened adsorption toward O*, O2*, and O3*. The spontaneous combination of O* and O2* is the main reason for enhanced EOP capacity on CuNi‐ATO. This work provides a novel insight into designing materials for efficient ozone production.

PM2.5 pollution modulates the response of ozone formation to VOC emitted from various sources: Insights from machine learning

Numerous studies have linked ozone (O3) production to its precursors and fine particulate matter (PM2.5), while the complex interaction effects of PM2.5 and volatile organic compounds (VOCs) on O3 remain poorly understood. A systematic approach based on an interpretable machine learning (ML) model was utilized to evaluate the primary driving factors that impact O3 and to elucidate how changes in PM2.5, VOCs from different sources, NOx, and meteorological conditions either promote or inhibit O3 formation through their individual and synergistic effects in a tropical coastal city, Haikou, from 2019 to 2020. The results suggest that under low PM2.5 levels, alongside the linear O3-PM2.5 relationship observed, O3 formation is suppressed by PM2.5 with higher proportions of traffic-derived aerosol. Vehicle VOC emissions contributed maximally to O3 formation at midday, despite the lowest concentration. VOCs from fossil fuel combustion and industry emissions, which have opposing effects on O3, act as inhibitors and promoters by inducing diverse photochemical regimes. As PM2.5 pollution escalates, the impact of these VOCs reverses, becoming more pronounced in shaping O3 variation. Sensitivity analysis reveals that the O3 formation regime is VOC-limited, and effective regional O3 mitigation requires prioritizing substantial VOC reductions to offset enhanced VOC sensitivity induced by the co-reduction in PM2.5, with a focus on industrial and vehicular emissions, and subsequently, fossil fuel combustion once PM2.5 is effectively controlled. This study underscores the potential of the SHAP-based ML approach to decode the intricate O3-NOx-VOCs-PM2.5 interplay, considering both meteorological and atmospheric compositional variations.

Elevated tropospheric ozone and crop production: potential negative effects and plant defense mechanisms.

Ozone (O3) levels on Earth are increasing because of anthropogenic activities and natural processes. Ozone enters plants through the leaves, leading to the overgeneration of reactive oxygen species (ROS) in the mesophyll and guard cell walls. ROS can damage chloroplast ultrastructure and block photosynthetic electron transport. Ozone can lead to stomatal closure and alter stomatal conductance, thereby hindering carbon dioxide (CO2) fixation. Ozone-induced leaf chlorosis is common. All of these factors lead to a reduction in photosynthesis under O3 stress. Long-term exposure to high concentrations of O3 disrupts plant physiological processes, including water and nutrient uptake, respiration, and translocation of assimilates and metabolites. As a result, plant growth and reproductive performance are negatively affected. Thus, reduction in crop yield and deterioration of crop quality are the greatest effects of O3 stress on plants. Increased rates of hydrogen peroxide accumulation, lipid peroxidation, and ion leakage are the common indicators of oxidative damage in plants exposed to O3 stress. Ozone disrupts the antioxidant defense system of plants by disturbing enzymatic activity and non-enzymatic antioxidant content. Improving photosynthetic pathways, various physiological processes, antioxidant defense, and phytohormone regulation, which can be achieved through various approaches, have been reported as vital strategies for improving O3 stress tolerance in plants. In plants, O3 stress can be mitigated in several ways. However, improvements in crop management practices, CO2 fertilization, using chemical elicitors, nutrient management, and the selection of tolerant crop varieties have been documented to mitigate O3 stress in different plant species. In this review, the responses of O3-exposed plants are summarized, and different mitigation strategies to decrease O3 stress-induced damage and crop losses are discussed. Further research should be conducted to determine methods to mitigate crop loss, enhance plant antioxidant defenses, modify physiological characteristics, and apply protectants.

Determination of Ozone Concentration Levels in Urban Environments Using a Laser Spectroscopy System

In urban areas, there has been a recent rise in ground-level ozone. Given its toxicity to both humans and the environment, the investigation of ozone pollution demands attention and should not be overlooked. Therefore, we conducted a study on ozone concentration in three distinct locations within the city of Magurele, Romania. This investigation considered variations in both structure and location during the spring and summer seasons, specifically at a breathing level of 1.5 m above the ground. Our analysis aimed to explore the impact of different locations and meteorological variables on ozone levels. The three measurement points were strategically positioned in diverse settings: within the city, in a forest, and within an industrial area. For these measurements, we used a laser spectroscopy system to determine the system’s sensitivity and selectivity and the influence of humidity in the detection of ozone in ambient air, which is a mixture of trace gases and water vapor. During the March–August campaign, the mean values in the three measuring points were 24.45 ± 16.44 ppb, 11.96 ± 3.80 ppb, and 95.01 ± 37.11 ppb. The peak concentrations of ozone were observed during the summer season. A diurnal analysis revealed that the atmospheric ozone levels were higher in the latter part of the day compared to the earlier part. These measurements suggest that the atmospheric temperature plays a significant role in tropospheric ozone production. Additionally, meteorological variables such as wind speed and direction were found to influence the ozone concentration. Remarkably, despite substantial traffic, the ozone levels remained consistently low throughout the entire period within the forested area. This observation may suggest the remarkable ability of trees to mitigate pollution levels.

Электрический озонатор-излучатель воздуха для сельскохозяйственных помещений:результаты исследований автономного модуля

The air environment of livestock buildings requires disinfection and improvement of the gas composition. The most effective method is ozonation. In order to improve the air inside livestock buildings, the authors have developed an electric ozonizer-emitter. Its emitter module consists of two ceramic bases with different-potential tungsten electrodes, one base having an electrode in the form of a honeycomb cell, and the other - in the form of a rod. The ozone productivity is regulated by changing the discharge gap between the emitter electrodes and the conducting plane. It has been theoretically established that ozone formation in a corona discharge depends on the electric field strength between the different-potential electrodes and their heating temperature. In this case, the maximum strength is achieved with a discharge gap from 25 to 35 mm and electrodes with a radius of no more than 2 mm. The effect of electrode heating temperature on ozone formation was studied on the developed design of the ozonizer-emitter in a laboratory of 180 m3 at an air temperature of 25°C above zero. The air gap between the electrodes was 30 mm, the voltage on the emitter varied from 10 to 30 kV, the duration of the ozonizer-emitter operation ranged between 0 and 80 min, the airflow rate induced by the electric fan was 0.3 m/s. It was experimentally established that stable operation of the ozonizer-emitter is observed when the electrode temperature does not exceed 30°C. In the future, the authors plan to introduce the ozonizer-air emitter into the ventilation and air conditioning system of agricultural buildings.

Regulation of the microenvironment of Pb2O3@Bi2O3-tube by structural reconstruction for boosting the electrochemical ozone production performance

The morphological reconfiguration of Pb2O3@Bi2O3-tube could optimized the surface microenvironment and enhanced electrochemical properties (FEO3 = 11.29%). And the excellent electrochemical degradation implied the potential environmental application of Pb2O3@Bi2O3-tube.

A quantum mechanical approach to the oxidation mechanism of graphene oxide (GO)

Elucidation of the reaction mechanism concerning the oxidation above the face and at the edge of a large, oxidized graphene (GO) cluster, namely C80H22O, by molecular oxygen in the first excited state (1Δg) was achieved with quantum mechanical calculations using the ONIOM two-layer method. Oxidation on the face of the aforementioned cluster leads to the formation of an ozone molecule, whereas oxygen molecule attack at the edge of the oxidized graphene surface either launches an ozonide —a five-membered ring species— formation during its outward approach or an 1,3-dioxetane —a four-membered ring species— production along its inward invasion. A detailed examination of the proposed pathways suggests that the ozonide formation should overcome almost one and a half times an adiabatic energy barrier with respect to the ozone production and is strongly exergonic by up to −50.1 kcal mol−1, supporting the experimental findings that both compounds are critically involved in the explosive deoxygenation of GO. On the other hand, the 1,3-dioxetane alternative pathway is considered even more exergonic, although it requires an overwhelming adiabatic energy barrier of 29.8 kcal mol−1 to accomplish its target.

Updating Biogenic Volatile Organic Compound (BVOC) Emissions With Locally Measured Emission Factors in South China and the Effect on Modeled Ozone and Secondary Organic Aerosol Production

AbstractBiogenic volatile organic compounds (BVOCs) emitted from terrestrial plants contribute substantially to ozone (O3) and secondary organic aerosol (SOA) formation in the troposphere. Accurate estimation of BVOC emissions is highly challengeable with a variety of uncertainties, one of which is the use of default emission factors (EFs) particularly for underrepresented regions without local data. In this study, locally measured BVOC‐EFs in south China, a subtropical region with abundant vegetation, were used to update regional BVOC emissions as estimated by the Model of Emissions of Gases and Aerosols from Nature (MEGAN). These EFs were recently determined in situ with characterized dynamic chambers for the emissions of isoprene, monoterpenes, and sesquiterpenes from tree species. The Community Multiscale Air Quality (CMAQ) model was then employed to see how much the regional O3 and SOA production is altered with the updated BVOC emissions. Results revealed lower BVOC emission estimates in south China when using the localized EFs than the MEGAN default ones, particularly for sesquiterpenes with a notable average reduction rate of approximately 40%. Using the updated BVOC emissions improved model O3 predictions in all seasons when compared to surface O3 monitoring, yet the lower BVOC emissions resulted in modeled O3 and SOA concentrations decreased by up to −6 ppb and −1.5 μg m−3, respectively, throughout south China. This study highlights the significance of localized EFs in refining emission estimates and air quality predictions in regions with a wealth of vegetation.

Observational Evidence of Unknown NOx Source and Its Perturbation of Oxidative Capacity in Bermuda's Marine Boundary Layer

AbstractNitrogen oxides (NOx) are key intermediates in the atmospheric cycling of reactive nitrogen, the spatiotemporal distribution of which modulates ozone (O3) production. Field campaigns were conducted at the Tudor Hill Marine Atmospheric Observatory, Bermuda, in the spring and summer of 2019 to explore atmospheric cycling of NOx and its modulation of photochemical O3 production in the marine boundary layer. In aged, clean marine air, an atypical NO2 diel profile with a solar noon peak of 69 ± 5 pptv was recorded, challenging the classic U‐shaped diel profile with a solar noon valley characterized by fast photolysis and oxidation consumption in the daytime. This result indicated an unknown daytime NOx source excluded from the current near‐explicit chemical model, which underestimated the solar noon NOx level by 20–56 pptv and source rate by 9.7–33.5 pptv hr−1, considering the upper and lower limits of total OH reactivity and halogen photochemistry in the marine boundary layer. The observed HONO level accounted for ∼56% of the unknown NOx source, implying an unknown NOx regeneration pathway with HONO as an intermediate. The photochemical nature of the unknown NOx source maximized perturbation of photochemical OH and O3 production. The O3 abundance and production rate were underestimated by 2–4 ppbv and 28%–80%, respectively, and the OH abundance and source rate were 7%–55% and 21%–57% lower than the estimated levels with the constraint of NOx, respectively. The unknown NOx source requires urgent revision of the current understanding of reactive nitrogen cycling and the oxidative capacity of the clean marine atmosphere.

Tuning Intermediate-Enriched microenvironment of pt-loaded porous TiN nanorods for enhanced electrochemical ozone production and hydrogen evolution reaction

Electrochemical ozone production (EOP) is a technology with great promise for ozone synthesis, where electrochemical anode and cathode reactions play key roles in electrolytic ozone generators. In this work, mesoporous three-dimensional Pt/TiN nanorods (NRs) have been designed and prepared for EOP and HER, exhibited impressive performance with the faraday efficiency of the anodic EOP was 13 %. The overpotential of cathodic HER was 38 mV at 10 mA·cm−2 with 0.5 M H2SO4. The porous structure of Pt/TiN NRs provides microenvironments favorable for enrichment of reaction intermediates, accelerating the kinetic processes of EOP and HER. Theoretical calculations have revealed that metal-support interactions (MSI) between Pt and TiN play an influential role in the adsorption of reactive intermediates. Furthermore, promising efficiencies in the electrochemical degradation of organic pollutants have been investigated, highlighting the potential application of the Pt/TiN NRs-1 || Pt/TiN NRs-2 in advanced electrochemical oxidation.

Study on Spatial Characteristics, Health Assessment, and Influencing Factors of Tropospheric Ozone Pollution in Qin–Jin Region, 2013–2022

Ozone is a pollutant that is harmful to human health and the troposphere. As a coal base in China, the study of ozone in the Qin–Jin region provides a scientific basis for pollution control and early warning and is of great practical significance. This paper analyzes the spatial and temporal distribution characteristics of tropospheric ozone in the Qin–Jin region from 2013 to 2022. It predicts the tropospheric ozone seasons in 2023 using a combination of ozone monitoring instruments (OMIs), ground stations, and machine learning. It also estimates the loss of health and economic benefits caused by ozone to humans, discusses the multiple factors affecting ozone changes, and identifies ozone-sensitive pollution control areas. The results showed that ozone in the Qin–Jin region spatially tends to increase from northwest to southeast, the Slope showed that ozone in the study area has a slightly increasing trend (0~0.079), the ozone concentration values are much larger than those in other months during the period of April–September, and there is no weekend effect. The predicted mean ozone values for 2023 are 36.57 DU in spring, 50.88 DU in summer, 34.29 DU in fall, and 30.10 DU in winter. The average values of all-cause mortality and economic losses are estimated to be 4591 and 4214 persons and 43.30 and 51.30 billion yuan in 2019 and 2021 in Shanxi Province, and 2498 and 1535 persons and 23.50 and 18.70 billion yuan in 2019 and 2021 in Shaanxi Province, respectively. Natural factors are positively correlated with ozone in the following order, temperature (TEM) &gt; precipitable water (TPW) &gt; vegetation cover (NDVI) &gt; relative humidity (RH), uplift index (LI) is negatively correlated with ozone, and barometric pressure (PS) is mainly uncorrelated. During the period of high ozone pollution in the Qin–Jin region (April–September), emissions of VOCs accelerated ozone production, and emissions of NOx suppressed ozone production in most areas. The high-value pollution period in the Qin–Jin area is mainly a VOC control area, and the synergistic control of NOx and VOCs is secondary.

HONO chemistry at a suburban site during the EXPLORE-YRD campaign in 2018: formation mechanisms and impacts on O3 production

Abstract. HONO is an important precursor for OH radicals that impact secondary-pollutant production. However, there are still large uncertainties about different HONO sources which hinder accurate predictions of HONO concentration and hence atmospheric oxidation capacity. Here HONO was measured during the EXPLORE-YRD campaign (EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation and their Effects in the Yangtze River Delta), along with other important parameters, enabling us to comprehensively investigate HONO variation characteristics and evaluate the relative importance of different HONO sources by using a box model. HONO showed significant variations, ranging from several tens of parts per thousand to 4.4 ppb. The average diurnal pattern of HONO / NOx showed a maximum of 0.17 around noon and resembled that of j(O1D), indicating the existence of photo-induced sources. Modeling simulations with only the default HONO source (OH + NO) largely underestimated HONO concentrations, with the modeled-averaged noontime HONO concentration an order of magnitude lower than the observed concentration. The calculated strength of the unknown HONO source (Punknown) showed a nearly symmetrical diurnal profile with a maximum of 2.5 ppb h−1 around noon. The correlation analysis and sensitivity tests showed that the photo-induced NO2 conversion on the ground was able to explain Punknown. Additional HONO sources incorporated into the box model improved the model's performance in simulating HONO concentrations. The revised box model reproduced the nighttime HONO concentration well but still underestimated the daytime HONO concentration. Further sensitivity tests indicated the underestimation of daytime HONO was not due to uncertainties of photo-induced NO2 uptake coefficients on the ground or aerosol surfaces or the enhancement factor of nitrate photolysis but was more likely due to other sources that were not considered in the model. Among the incorporated HONO sources and the default gas-phase source, photo-induced NO2 conversion on the ground dominated the modeled HONO production during the daytime, accounting for 71 % of the total, followed by NO + OH, NO2 hydrolysis on the ground surface, vehicle emissions, photo-induced NO2 conversion on the aerosol surface, nitrate photolysis and NO2 hydrolysis on the aerosol surface. NO2 hydrolysis on the ground surface was the major source of nighttime HONO, contributing 55 % of total HONO production. HONO photolysis contributed 43 % of ROx production during the daytime, followed by O3 photolysis (17 %), HCHO photolysis (14 %), ozonolysis of alkenes (12 %) and carbonyl photolysis (10 %). With observed HONO as a model constraint, the average peak of net ozone production rate increased by 88 % to 12.6 ppb h−1 compared to that without observed HONO as a model constraint, indicating HONO evidently enhanced O3 production and hence aggravated O3 pollution in summer seasons. Our study emphasized the importance of heterogeneous NO2 conversion on the ground surface in HONO production and accurate parameterization of HONO sources in predicting secondary-pollutant production.

Spatial Distribution of Multiple Atmospheric Pollutants in China from 2015 to 2020

The pursuit of higher-resolution and more reliable spatial distribution simulation results for air pollutants is important to human health and environmental safety. However, the lack of high-resolution remote sensing retrieval parameters for gaseous pollutants (sulfur dioxide and ozone) limits the simulation effect to a 1 km resolution. To address this issue, we sequentially generated and optimized the spatial distributions of near-surface PM2.5, SO2, and ozone at a 1 km resolution in China through two approaches. First, we employed spatial sampling, random ID, and parameter convolution methods to jointly optimize a tree-based machine-learning gradient-boosting framework, LightGBM, and improve the performance of spatial air pollutant simulations. Second, we simulated PM2.5, used the simulated PM2.5 result to simulate SO2, and then used the simulated SO2 to simulate ozone. We improved the stability of 1 km-resolution SO2 and ozone products through the proposed sequence of multiple-pollutant simulations. The cross-validation (CV) of the random sample yielded an R2 of 0.90 and an RMSE of 9.62 µg∙m−3 for PM2.5, an R2 of 0.92 and an RMSE of 3.9 µg∙m−3 for SO2, and an R2 of 0.94 and an RMSE of 5.9 µg∙m−3 for ozone, which are values better than those in previous related studies. In addition, we tested the reliability of PM2.5, SO2, and ozone products in China through spatial distribution reliability analysis and parameter importance reliability analysis. The PM2.5, SO2, and ozone simulation models and multiple-air-pollutant (MuAP) products generated by the two optimization methods proposed in this study are of great value for long-term, large-scale, and regional-scale air pollution monitoring and predictions, as well as population health assessments.