Three-dimensional Air Quality Research Articles

Three-Dimensional Air Quality Monitoring and Simulation of Campus Microenvironment Based on UAV Platform

This study innovatively employs drones equipped with air quality sensors to collect three-dimensional air quality data in a campus microenvironment. Data are accurately corrected using a BP neural network, and a cubic model is constructed using three-dimensional interpolation. Combining photogrammetry technology, this study analyzes air quality patterns, finding significant differences from macro trends. Construction activities and large electronic experimental equipment significantly increase PM2.5 levels in the air. In rainy weather, the respiration of vegetation is enhanced, leading to higher CO2 concentrations, while water bodies exhibit higher temperatures in rainy weather due to their high specific heat capacity. This research not only provides a new perspective for microenvironment air quality monitoring but also offers a scientific basis for future air quality monitoring and management.

Differences of Three Methods in Determining Ozone Sensitivity in Nanjing

In recent years， ozone （O3） has become an increasingly important air pollutant in China. Identifying the sensitivity of O3 to the precursors volatile organic compounds （VOCs） and nitrogen oxides （NOx） can help make effective abatement strategies. This study compared three methods for determining O3-VOCs-NOx sensitivity： simulated photochemical indicator values and sensitivity coefficients derived from a three-dimensional air quality model and an observation-based model （OBM）， with a case study involving an O3 pollution event that occurred in Nanjing in late July 2017. The results showed that O3 sensitivity based on the photochemical indicator and sensitivity coefficients demonstrated similar spatial variations （over 50% of the grid cells of Nanjing exhibiting identical O3 sensitivity）. However， sensitivity coefficients identified a larger number of areas within a transitional O3 sensitivity regime， as opposed to the VOCs- or NOx-limited regime identified by the photochemical indicator. The determination of the latter was affected by the adopted threshold values. The OBM relied on the quality of the observational data. For example， positive biases in observed NO2 could lead to an underestimation of O3 sensitivity to NOx with the OBM. During the high pollution period， the three methods exhibited significant disparities. The photochemical indicator tended to suggest the VOCs-limited condition， whereas the OBM and sensitivity coefficients indicated the NOx-limited or transitional regimes.

The effects of coastal local circulations and their interactions on ozone pollution in the Hangzhou metropolitan area

Impacts of coastal local circulations and their interactions on ozone (O3) in Hangzhou on 5 June 2018 with relatively low temperatures were investigated using surface observations and three-dimensional air quality simulations. Local circulations and their interactions were primary causes of the episode instead of high temperatures. Northwesterly land breeze on the previous day transported O3 to sea, and sea breeze (SB) on the episode day blew pollution back to land. Inland penetration (east to west) of the combined SB front (SBF) was accelerated by urban heat island (UHI) induced easterly flow over coast and slowed by its westerly flow and surface roughness over inland urban areas. O3 accumulation at surface and in the elevated air over city was caused by mountain barrier effect and venting process. Subsidence heating associated with valley circulation accelerated UHI circulation (UHIC) before 1400 LT, indirectly strengthening the SB circulation (SBC). The UHIC and valley circulation decoupled with SBC at noon and in the late afternoon, respectively, leading to a stronger SBC. The stronger SBC brought additional O3 (>20 ppb) to further inland area, to elevated air with updrafts in SB head, and to nocturnal stable boundary layer and residual layer with its upper-level offshore flow.

Source apportionment of ambient concentration and population exposure to elemental carbon in South Korea using a three-dimensional air quality model

We quantified the foreign and domestic contributions to annual mean elemental carbon (EC) concentration over South Korea in 2016 using the Primary Carbon Appointment tool in the community multiscale air quality model. The individual domestic contributions were further examined by emission source category (area, mobile, and point) in each sub-region (i.e., Seoul Metropolitan Area (SMA), Gangwon, Chungcheong, Youngnam, and Honam). EC contribution and population-weighted exposure contribution (PWEC) for each emission source were calculated. Two indicators were compared and adjusted considering uncertainties of emissions from sub-regions. Based on the results of this analysis, the primary EC emission sources that need to be managed to alleviate the concentrations and PWECs were classified, and the cost-effectiveness was compared with contribution rates for EC and PWEC. The modeled annual mean EC concentration in South Korea was 0.6 µg/m3, of which 54% was contributed by foreign sources (0.3 µg/m3). However, the quarterly foreign contribution differed by up to five times depending on the monsoon, while the domestic contribution did not. Simultaneously, spatial variations of the annual mean EC contributions are smaller than those of the foreign contributions. Regardless of the uncertainty of emissions, domestic PWEC was 20% higher than the domestic concentration as domestic EC emissions were concentrated in densely populated areas. It implies that EC emission control has more significant meaning not only to improve concentration but also to improve population exposure. In addition, the contribution rate showed greater variation between sub-regions than the EC emission source categories within a region. Considering this, if the cost used to reduce a unit EC emission is the same, the cost effect can be expected when EC emissions are reduced in the sub-regions with a large contribution rate regardless of EC emission source category.

An Internet of Things Sensor Array for Spatially and Temporally Resolved Indoor Climate Measurements.

The COVID-19 pandemic has emphasized the need for infection risk analysis and assessment of ventilation systems in indoor environments based on air quality criteria. In this context, simulations and direct measurements of CO2 concentrations as a proxy for exhaled air can help to shed light on potential aerosol pathways. While the former typically lack accurate boundary conditions as well as spatially and temporally resolved validation data, currently existing measurement systems often probe rooms in non-ideal, single locations. Addressing both of these issues, a large and flexible wireless array of 50 embedded sensor units is presented that provides indoor climate metrics with configurable spatial and temporal resolutions at a sensor response time of 20 s. Augmented by an anchorless self-localization capability, three-dimensional air quality maps are reconstructed up to a mean 3D Euclidean error of 0.21 m. Driven by resolution, ease of use, and fault tolerance requirements, the system has proven itself in day-to-day use at ETH Zurich, where topologically differing auditoria (at-grade, sloped) were investigated under real occupancy conditions. The corresponding results indicate significant spatial and temporal variations in the indoor climate rendering large sensor arrays essential for accurate room assessments. Even in well-ventilated auditoria, cleanout time constants exceeded 30 min.

Impacts of synoptic forcing and topography on aerosol pollution during winter in Shenyang, Northeast China

Northeast China frequently experiences aerosol pollution episodes in winter. In addition to the pollutant emissions, synoptic pattern and topography can impact the air quality in complex ways, which are still not well understood in Northeast China. Therefore, the impacts of synoptic forcing and topography on aerosol pollution in Shenyang were investigated combining surface observations, sounding measurements, and three-dimensional air quality simulations. The studied pollution episode occurred from January 1 to 5, 2020, along with poor meteorological dispersion conditions characterized by weak winds, strong thermal stabilities, and shallow planetary boundary layers (PBLs). During the formation of pollution, strong elevated thermal inversion layers were observed over Shenyang, induced by the large-scale synoptic pattern, which suppressed the PBL growth and the vertical dispersion of aerosols. Moreover, the blocking effect of mountains to the east of Shenyang further worsened the pollution when northwesterly/westerly flows prevailed in shallow PBLs. Numerical sensitive experiment was conducted to estimate the contribution of blocking effect of mountains to the near-surface PM2.5 concentration in Shenyang, and it was found that around one third of PM2.5 concentration during January 1–4 was relevant to the terrain effect. These findings can facilitate a comprehensive understanding of the physical formation of aerosol pollution in Northeast China and helpful for the pollution controls.

The role of a distant typhoon in extending a high PM2.5 episode over Northeast Asia

In Northeast Asia, high-pressure systems typically initiate high PM2.5 episodes. However, the role of low-pressure systems, including typhoons, in high PM2.5 episodes is not well understood. In this study, we attempted to explain the evolution of the high PM2.5 episode event that was initiated by a migratory high-pressure system and the extension of the event in the presence of low-pressure systems. To achieve this aim, we conducted a multilateral analysis of a high PM2.5 episode that occurred in October 2015 in Northeast Asia using surface observation data, satellite measurements, weather maps, trajectory analyses, and three-dimensional air quality simulations. The analysis results revealed the discrete steps of the event. First, air pollutants over inland China were transported to Northern China by an anticyclone in the region. Then, in Northern China, elevated PM2.5 concentrations were observed in the following 2–3 days due to local emissions under the enhanced stagnant conditions in addition to the transported air pollution from inland China. Subsequently, under the influence of a slow-moving migratory high-pressure system in China, South Korea (a downwind area of China) experienced a high (>50 μg/m3) PM2.5 episode due to the transboundary transport of PM2.5 and local emissions. Usually, high PM2.5 episodes in South Korea under similar meteorological conditions last up to five days. However, during this period, the synoptic displacement of the high-/low pressure systems at 35°–38° latitudes in the region caused an extended (e.g., four or more days) of air pollutant residence time in Northeast Asia. Further, Typhoon Champi located in the northern Pacific (about 500 km south of Japan) interfered with the eastward movement of the high-pressure system located in the downwind area, which resulted in poor ventilation conditions for PM2.5 and its precursors. Thus, we determined that Typhoon Champi played a crucial role in maintaining PM2.5 concentrations over 50 μg/m3 for nine days or longer. We also noted that the aforementioned steps also occurred for another extended PM2.5 episode under the influence of a distant low-pressure system in the past. The findings of this study warrant further investigation of the relationship between extended PM2.5 episodes in Northeast Asia and distant typhoons.

Comparison of three aerosol representations of NHM-Chem (v1.0) for the simulations of air quality and climate-relevant variables

Abstract. This study provides comparisons of aerosol representation methods incorporated into a regional-scale nonhydrostatic meteorology–chemistry model (NHM-Chem). Three options for aerosol representations are currently available: the five-category non-equilibrium (Aitken, soot-free accumulation, soot-containing accumulation, dust, and sea salt), three-category non-equilibrium (Aitken, accumulation, and coarse), and bulk equilibrium (submicron, dust, and sea salt) methods. The three-category method is widely used in three-dimensional air quality models. The five-category method, the standard method of NHM-Chem, is an extensional development of the three-category method and provides improved predictions of variables relating to aerosol–cloud–radiation interaction processes by implementing separate treatments of light absorber and ice nuclei particles, namely, soot and dust, from the accumulation- and coarse-mode categories (implementation of aerosol feedback processes to NHM-Chem is still ongoing, though). The bulk equilibrium method was developed for operational air quality forecasting with simple aerosol dynamics representations. The total CPU times of the five-category and three-category methods were 91 % and 44 % greater than that of the bulk method, respectively. The bulk equilibrium method was shown to be eligible for operational forecast purposes, namely, the surface mass concentrations of air pollutants such as O3, mineral dust, and PM2.5. The simulated surface concentrations and depositions of bulk chemical species of the three-category method were not significantly different from those of the five-category method. However, the internal mixture assumption of soot/soot-free and dust/sea salt particles in the three-category method resulted in significant differences in the size distribution and hygroscopicity of the particles. The unrealistic dust/sea salt complete mixture of the three-category method induced significant errors in the prediction of the mineral dust-containing cloud condensation nuclei (CCN), which alters heterogeneous ice nucleation in cold rain processes. The overestimation of soot hygroscopicity by the three-category method induced errors in the BC-containing CCN, BC deposition, and light-absorbing aerosol optical thickness (AAOT). Nevertheless, the difference in AAOT was less pronounced with the three-category method because the overestimation of the absorption enhancement was compensated by the overestimation of hygroscopic growth and the consequent loss due to in-cloud scavenging. In terms of total properties, such as aerosol optical thickness (AOT) and CCN, the results of the three-category method were acceptable.

Characteristics of regional transport during two-year wintertime haze episodes in North China megacities

A three-dimensional air quality model coupled with an on-line source-tagged module was adopted to investigate the source-receptor relationship in North China during the winter of 2017 and 2018. The total contribution of cities located along transport pathway (the “2 + 26” cities) accounts for most of the fine particulate matter (PM2.5) across this region both on average and during haze episodes. Regional joint prevention and control strategies are crucial to both routine and emergency environmental governance. Compared to primary PM2.5, secondary compounds may be transported across greater distances and impose notable effects in downstream areas. In regard to the secondary inorganic aerosols (SIA) in Beijing during haze episodes, regional transport plays a more important role than do local emissions. The contribution of the transport of particle-phase secondary pollutants is comparable to that of the transport of gas-phase precursors during haze episodes. Control measurements of gas-phase precursors in upstream areas are also important, and they benefit the reduction in the total PM2.5 level.

Impacts of atmospheric vertical structures on transboundary aerosol transport from China to South Korea

To forecast haze pollution episodes caused by high concentrations of long-range transported pollutants emitted in the areas upstream of South Korea, it is crucial to study and identify their behaviour. We analysed the three-dimensional air quality structure in Seoul using ground observation data and aerosol lidar measurements to identify vertical aerosol intrusion into the Korean Peninsula during the spring of 2016. The intrusions were particularly affected by the development of the atmospheric boundary layer (ABL) in the leeward regions. The nocturnal pollutant intrusion into the Korean peninsula via the Yellow Sea was examined using measured data. The pollutants first reached the area above the nocturnal boundary layer (548 ± 180 m) and approached ground level on the following day due to convective mixing depending on the convective ABL growth (1182 ± 540 m) in daytime. These intrusion mechanisms were mostly attributed to extremely high concentrations (i.e. >100 μg m−3) of fine particulate matter in the leeward regions, accounting for four of the total of six cases for which the warnings and alerts were issued in Seoul Metropolitan Area over a year-long period (2016). The horizontal and vertical pathways of the long-range transported pollutants and the atmospheric vertical structure were identified as key factors affecting the surface air quality concentration in the leeward regions.

Optimization of vertical grid setting for air quality modelling in China considering the effect of aerosol-boundary layer interaction

The feedback between ambient aerosols and planetary boundary layer (PBL) meteorology has been proven to play a critical role in the enhancement of haze pollution. Vertical distribution of aerosols as well as temperature stratification are vital to understand aerosol – boundary layer interaction (ABI) and its impact on air quality deterioration. In current regional air quality models, the default vertical grid setting is relatively coarse and decreases progressively with altitude. However, the ABI is sensitive to aerosol layer at specific altitudes, i.e. around the top of PBL. This work aims to explore optimized vertical grid setting for better characterizing ABI and its role in air quality degradation. A single column model (SCM) is used for sensitivity tests considering the balance between model performance and computational cost. This optimized grid setting is then applied in three-dimensional air quality modelling in eastern China. Compared with default configuration, the optimized one is demonstrated to perform much better in characterizing temperature stratification and extreme fine particle (PM2.5) concentration as well as its diurnal variation during haze episodes. Specifically, the averaged decrease in PBL height and increment in surface PM2.5 concentration are about 5% and 20% while applying optimized setting, thereby reducing the mean bias from 30 to 5 μg/m3 in PM2.5 concentration. The improvements could be attributed mainly to more accurate profiles of aerosol and its heating effect, and thus stabilized lower atmosphere. The optimization of vertical grid setting could be applied to areas with high concentration of absorbing aerosols such as eastern China and India, which could help better predict extreme near-surface pollution episodes.

Modeling the effect of non-ideality, dynamic mass transfer and viscosity on SOA formation in a 3-D air quality model

Abstract. In this study, assumptions (ideality and thermodynamic equilibrium) commonly made in three-dimensional (3-D) air quality models were reconsidered to evaluate their impacts on secondary organic aerosol (SOA) formation over Europe. To investigate the effects of non-ideality, dynamic mass transfer and aerosol viscosity on the SOA formation, the Secondary Organic Aerosol Processor (SOAP) model was implemented in the 3-D air quality model Polyphemus. This study presents the first 3-D modeling simulation which describes the impact of aerosol viscosity on the SOA formation. The model uses either the equilibrium approach or the dynamic approach with a method specially designed for 3-D air quality models to efficiently solve particle-phase diffusion when particles are viscous. Sensitivity simulations using two organic aerosol models implemented in Polyphemus to represent mass transfer between gas and particle phases show that the computation of the absorbing aerosol mass strongly influences the SOA formation. In particular, taking into account the concentrations of inorganic aerosols and hydrophilic organic aerosols in the absorbing mass of the aqueous phase increases the average SOA concentration by 5 % and 6 %, respectively. However, inorganic aerosols influence the SOA formation not only because they constitute an absorbing mass for hydrophilic SOA, but also because they interact with organic compounds. Non-ideality (short-, medium- and long-range interactions) was found to influence SOA concentrations by about 30 %. Concerning the dynamic mass transfer for the SOA formation, if the viscosity of SOA is not taken into account and if ideality of aerosols is assumed, the dynamic approach is found to give generally similar results to the equilibrium approach (indicating that equilibrium is an efficient hypothesis for inviscid and ideal aerosols). However, when a non-ideal aerosol is assumed, taking into account the dynamic mass transfer leads to a decrease of concentrations of the hydrophilic compounds (compared to equilibrium). This decrease is due to differences in the values of activity coefficients, which are different between values computed for bulk aerosols and those for each size section. This result indicates the importance of non-ideality on the dynamic evolution of SOA. For viscous aerosols, assuming a highly viscous organic phase leads to an increase in SOA concentrations during daytime (by preventing the evaporation of the most volatile organic compounds). The partitioning of nonvolatile compounds is not affected by viscosity, but the aging of more volatile compounds (that leads to the formation of the less volatile compounds) slows down as the evaporation of those compounds is stopped due to the viscosity of the particle. These results imply that aerosol concentrations may deviate significantly from equilibrium as the gas–particle partitioning could be higher than predicted by equilibrium. Furthermore, although a compound evaporates in the simulation using the equilibrium approach, the same compound can condense in the simulation using the dynamic approach if the particles are viscous. The results of this study emphasize the need for 3-D air quality models to take into account the effect of non-ideality on SOA formation and the effect of aerosol viscosity for the more volatile fraction of semi-volatile organic compounds.

Simulated sensitivity of secondary organic aerosol in the South Coast Air Basin of California to nitrogen oxides and other chemical parameters

ABSTRACTSensitivity of secondary organic aerosol (SOA) concentrations in the South Coast Air Basin (SoCAB) of California to nitrogen oxide (NOx) emission is simulated using gas-phase chemistry and gas-particle partitioning modules. These modules are implemented into a three-dimensional air quality model applied for high-pollution summer meteorology and 2008 emissions. To test sensitivity, NOx emissions in all locations and at all times are scaled by factors ranging from 0.1 to 10.0 in separate model runs. The basin-wide average SOA concentration exhibits a ‘turnover’ NOx emission multiplicative factor, above and below which the average SOA concentration decreases. For the entire SoCAB, this critical NOx emission factor is ∼0.3; while the magnitude of SOA concentrations changes with time, this peak value (∼0.2–0.3) appears to be relatively independent of the hour of the simulated day. When considering individual locations within the SoCAB, this peak factor shows a slightly broader range. Projected emission...

Explaining the spatiotemporal variation of fine particle number concentrations over Beijing and surrounding areas in an air quality model with aerosol microphysics

In this study, a three-dimensional air quality model with detailed aerosol microphysics (NAQPMS + APM) was applied to simulate the fine particle number size distribution and to explain the spatiotemporal variation of fine particle number concentrations in different size ranges over Beijing and surrounding areas in the haze season (Jan 15 to Feb 13 in 2006). Comparison between observations and the simulation indicates that the model is able to reproduce the main features of the particle number size distribution. The high number concentration of total particles, up to 26600 cm−3 in observations and 39800 cm−3 in the simulation, indicates the severity of pollution in Beijing. We find that primary particles with secondary species coating and secondary particles together control the particle number size distribution. Secondary particles dominate particle number concentration in the nucleation mode. Primary and secondary particles together determine the temporal evolution and spatial pattern of particle number concentration in the Aitken mode. Primary particles dominate particle number concentration in the accumulation mode. Over Beijing and surrounding areas, secondary particles contribute at least 80% of particle number concentration in the nucleation mode but only 10–20% in the accumulation mode. Nucleation mode particles and accumulation mode particles are anti-phased with each other. Nucleation or primary emissions alone could not explain the formation of the particle number size distribution in Beijing. Nucleation has larger effects on ultrafine particles while primary particles emissions are efficient in producing large particles in the accumulation mode. Reduction in primary particle emissions does not always lead to a decrease in the number concentration of ultrafine particles. Measures to reduce fine particle pollution in terms of particle number concentration may be different from those addressing particle mass concentration.

Influence of tree crown characteristics on the local PM10 distribution inside an urban street canyon in Antwerp (Belgium): A model and experimental approach

Apart from influencing the amount of leaf-deposited particles, tree crown morphology will influence the local distribution of atmospheric particles. Nevertheless, tree crowns are often represented very rudimentary in three-dimensional air quality models. Therefore, the influence of tree crown representation on the local ambient PM10 concentration and resulting leaf-deposited PM10 mass was evaluated, using the three-dimensional computational fluid dynamics (CFD) model ENVI-met® and ground-based LiDAR imaging. The modelled leaf-deposited PM10 mass was compared to gravimetric results within three different particle size fractions (0.2–3, 3–10 and >10μm), obtained at 20 locations within the tree crown. Modelling of the LiDAR-derived tree crown resulted in altered atmospheric PM10 concentrations in the vicinity of the tree crown. Although this model study was limited to a single tree and model configuration, our results demonstrate that improving tree crown characteristics (shape, dimensions and LAD) affects the resulting local PM10 distribution in ENVI-met. An accurate tree crown representation seems, therefore, of great importance when aiming at modelling the local PM distribution.

Source attribution and quantification of benzene event emissions in a Houston ship channel community based on real-time mobile monitoring of ambient air

ABSTRACTA mobile laboratory equipped with a proton transfer reaction mass spectrometer (PTR-MS) operated in Galena Park, Texas, near the Houston Ship Channel during the Benzene and other Toxics Exposure Study (BEE-TEX). The mobile laboratory measured transient peaks of benzene of up to 37 ppbv in the afternoon and evening of February 19, 2015. Plume reconstruction and source attribution were performed using the four-dimensional (4D) variational data assimilation technique and a three-dimensional (3D) micro-scale forward and adjoint air quality model based on mobile PTR-MS data and nearby stationary wind measurements at the Galena Park Continuous Air Monitoring Station (CAMS). The results of inverse modeling indicate that significant pipeline emissions of benzene may at least partly explain the ambient concentration peaks observed in Galena Park during BEE-TEX. Total pipeline emissions of benzene inferred within the 16-km2 model domain exceeded point source emissions by roughly a factor of 2 during the observational episode. Besides pipeline leaks, the model also inferred significant benzene emissions from marine, railcar, and tank truck loading/unloading facilities, consistent with the presence of a tanker and barges in the Kinder Morgan port terminal during the afternoon and evening of February 19. Total domain emissions of benzene exceeded corresponding 2011 National Emissions Inventory (NEI) estimates by a factor of 2–6.Implications: Port operations involving petrochemicals may significantly increase emissions of air toxics from the transfer and storage of materials. Pipeline leaks, in particular, can lead to sporadic emissions greater than in emission inventories, resulting in higher ambient concentrations than are sampled by the existing monitoring network. The use of updated methods for ambient monitoring and source attribution in real time should be encouraged as an alternative to expanding the conventional monitoring network.

Development and case study of a science-based software platform to support policy making on air quality

This article describes the development and implementations of a novel software platform that supports real-time, science-based policy making on air quality through a user-friendly interface. The software, RSM-VAT, uses a response surface modeling (RSM) methodology and serves as a visualization and analysis tool (VAT) for three-dimensional air quality data obtained by atmospheric models. The software features a number of powerful and intuitive data visualization functions for illustrating the complex nonlinear relationship between emission reductions and air quality benefits. The case study of contiguous U.S. demonstrates that the enhanced RSM-VAT is capable of reproducing the air quality model results with Normalized Mean Bias <2% and assisting in air quality policy making in near real time.

Application of photochemical indicators to evaluate ozone nonlinear chemistry and pollution control countermeasure in China

Ozone sensitivity in China was investigated by using a comprehensive three-dimensional air quality model system WRF-CALGRID. A real case and two cases with 35% emission reduction for either NOx or VOC were conducted for the period of March in 2010. The simulation results of O3 agreed fairly well with the observation data. Based on the meaning of O3 sensitivity, the ratio Ra was defined, with the transition value of 1 to distinguish NOx-sensitive region from VOC-sensitive region. With the aid of Ra, VOC- and NOx-sensitive regions in China were preliminary located. The transition ranges for some photochemical indicators were quantified. Only those of H2O2/NOz and H2O2/HNO3 met the requirement that the 95th percentile VOC-sensitive value should be equal to or lower than the 5th percentile NOx-sensitive value. 0.16–0.40 for H2O2/HNO3 and 0.14–0.28 for H2O2/NOz were adopted to distinguish different O3 sensitivity in China. The results showed that the VOC-sensitive regions are primarily distributed over the urban centers and the developed industrial areas in eastern and southern China, while the NOx-sensitive regions are mainly located in the remote areas of northern and western China. High correlation between Ra and indicators was found, and a new approach to quantify the transition values of indicators was proposed. These indicators can play an important role in the air complex pollution control of urban clusters over East Asia.

Impacts of uncertainty in AVOC emissions on the summer ROx budget and ozone production rate in the three most rapidly-developing economic growth regions of China

High levels of uncertainty in non-methane volatile organic compound (NMVOC) emissions in China could lead to significant variation in the budget of the sum of hydroxyl (OH) and peroxy (HO2, RO2) radicals (ROx = OH + HO2 + RO2) and the ozone production rate [P(O3)], but few studies have investigated this possibility, particularly with three-dimensional air quality models. We added diagnostic variables into the WRF-Chem model to assess the impact of the uncertainty in anthropogenic NMVOC (AVOC) emissions on the ROx budget and P(O3) in the Beijing-Tianjin-Hebei region, Yangtze River Delta, and Pearl River Delta of China. The WRF-Chem simulations were compared with satellite and ground observations, and previous observation-based model studies. Results indicated that 68% increases (decreases) in AVOC emissions produced 4%–280% increases (2%–80% decreases) in the concentrations of OH, HO2, and RO2 in the three regions, and resulted in 35%–48% enhancements (26%–39% reductions) in the primary ROx production and ∼ 65% decreases (68%–73% increases) of the P(O3) in Beijing, Shanghai, and Guangzhou. For the three cities, the two largest contributors to the ROx production rate were the reaction of O1D + H2O and photolysis of HCHO, ALD2, and others; the reaction of OH + NO2 (71%–85%) was the major ROx sink; and the major contributor to P(O3) was the reaction of HO2 + NO (∼ 65%). Our results showed that AVOC emissions in 2006 from Zhang et al. (2009) have been underestimated by ∼ 68% in suburban areas and by 〉 68% in urban areas, implying that daily and hourly concentrations of secondary organic aerosols and inorganic aerosols could be substantially underestimated, and cloud condensation nuclei could be underestimated, whereas local and regional radiation was overestimated.

The Ozone–Climate Penalty: Past, Present, and Future

Climate change is expected to increase global mean temperatures leading to higher tropospheric ozone (O3) concentrations in already polluted regions, potentially eroding the benefits of expensive emission controls. The magnitude of the "O3-climate penalty" has generally decreased over the past three decades, which makes future predictions for climate impacts on air quality uncertain. Researchers attribute historical reductions in the O3-climate penalty to reductions in NOx emissions but have so far not extended this theory into a quantitative prediction for future effects. Here, we show that a three-dimensional air quality model can be used to map the behavior of the O3-climate penalty under varying NOx and VOC emissions in both NOx-limited and NOx-saturated conditions in Central and Southern California, respectively. Simulations suggest that the planned emissions control program for O3 precursors will not diminish the O3-climate penalty to zero as some observational studies might imply. The results further demonstrate that in a NOx-limited air basin, NOx control strategies alone are sufficient to both decrease the O3-climate penalty and mitigate O3 pollution, while in a NOx-saturated air basin, a modified emissions control plan that carefully chooses reductions in both NOx and VOC emissions may be necessary to eliminate the O3-climate penalty while simultaneously reducing base case O3 concentrations to desired levels. Additional modeling is needed to determine the behavior of the O3-climate penalty as NOx and VOC emissions evolve in other regions.