Ozone Measurements Research Articles

Consumption of Hydrocarbons and Its Relationship with Ozone Formation in Two Chinese Megacities

Continuous measurements of ozone and its precursors were performed at sites in two Chinese megacities, i.e., an urban site in Beijing and a suburban site in the Pearl River Delta (PRD). At both sites, the total oxidants (O3 + NO2) varied with the ratio of ethylbenzene to m,p-xylenes, which serves as an indicator of photochemical aging. An observation-based method (OBM) was derived for calculating the photochemical consumption of individual non-methane hydrocarbons (NMHCs) based on the observed NMHC concentrations and the ratio of ethylbenzene to m,p-xylenes. The results show a strong correlation between the oxidant level and the derived consumption of precursors at the two sites (R2 = 0.81 for the PRD site and R2 = 0.83 for the Beijing site), demonstrating a strong cause–effect relationship. The relative “consumption efficiency” among NMHCs was calculated based on the integrated amount of hydroxyl radicals derived from the ratio of ethylbenzene to xylenes. Thus, the percent contributions to ozone formation from each individual NMHC can be calculated. This concept of consumption is purely observation-based and provides an easy way to bypass complicated modeling and the necessity of knowing instantaneous concentrations of hydroxyl radicals, which are highly illusive in nature.

Changes in ozone photochemical regime in Fresno, California from 1994 to 2018 deduced from changes in the weekend effect

Significant progress has been made in reducing emissions of air pollutants in the San Joaquin Valley in California. Nevertheless, from May to October, the valley still experiences numerous exceedances of the ozone health standard. As the standards are tightened, it is becoming harder to design policies to attain them. To better understand historical emissions reductions in the context of necessary future control efforts, we analyze 25 years of hourly measurements of ozone and nitrogen oxides concentrations for the hottest one third of days in Fresno using multiple linear regression analysis. We then analyze the changing dynamics of the weekend effect over the years in order to evaluate the growing importance of day-to-day carryover on ozone concentrations. A simplified model of the day-of-week pattern of ozone concentrations is used to explore the impact of same-day and previous-day concentrations. In addition to ozone, Ox (O3 + NO2) is used to distinguish reductions of atmospheric oxidants from short-duration exchanges between O3 and NO2. The analysis shows that there has been a significant increase in the importance of day-to-day carryover on ozone levels, and that consequently the ozone weekend effect in Fresno has changed over the last 25 years. In the 1990s, lower NOx on the weekend led to increased ozone on Saturdays and Sundays but levels of Ox remained constant. In the 2010s, lower weekend NOx led to reduced ozone on Saturdays, Sundays and Mondays showing that reductions in primary pollutants are sufficient to yield immediate decreases in secondary pollutants. Overall, the photochemical regime in the atmosphere has evolved such that carryover and regional pollution will be increasingly important in determining local ozone concentrations. Policies will therefore need to pay greater attention to regional emissions as local reductions may not be sufficient to meet the health standard.

Analysis of Insulation Diagnosis for Generator-Motor Stator Winding in Pumped Storage Power Plant

In this study, insulation diagnostic tests were conducted on pumped storage power plant (PSPP) generator-motor stator bars with artificially simulated defects in order to improve solutions to perform preventive maintenance and track insulation diagnostic data for generator-motors by proving the effectiveness of insulation indices. Moreover, ozone (O3) concentration was estimated in order to relate it to partial discharge (PD) in laboratory to ensure the effectiveness of ozone as another index for insulation deterioration. By performing an offline PD test and ultraviolet (UV) observation on one of the generator-motors during overhaul, and an ozone concentration measurement for the identical machine after the overhaul, it was concluded that ozone estimation could be a powerful index for insulation diagnosis under actual operational conditions. It was further developed that ozone measurement is useful to detect not only discharges in slots as mentioned in some studies but also discharges at the end-winding as proven in this study. The findings of this study are expected to contribute to more reliable maintenance of generator-motors in PSPPs by achieving elaborate insulation diagnosis via multiple diagnostic indices.

On the Smoothing of the Generalized Extreme Value Distribution Parameters Using Penalized Maximum Likelihood: A Case Study on UVB Radiation Maxima in the Mexico City Metropolitan Area

This paper concerns the use and implementation of penalized maximum likelihood procedures to fitting smoothing functions of the generalized extreme value distribution parameters to analyze spatial extreme values of ultraviolet B (UVB) radiation across the Mexico City metropolitan area in the period 2000–2018. The model was fitted using a flexible semi-parametric approach and the parameters were estimated by the penalized maximum likelihood (PML) method. In order to investigate the performance of the model as well as the estimation method in the analysis of complex nonlinear trends for UVB radiation maxima, a simulation study was conducted. The results of the simulation study showed that penalized maximum likelihood yields better regularization to the model than the maximum likelihood estimates. We estimated return levels of extreme UVB radiation events through a nonstationary extreme value model using measurements of ozone (O3), nitrogen oxides (NOx), particles of 10 μm or less in diameter (PM10), carbon monoxide (CO), relative humidity (RH) and sulfur dioxide (SO2). The deviance statistics indicated that the nonstationary generalized extreme value (GEV) model adjusted was statistically better compared to the stationary model. The estimated smoothing functions of the location parameter of the GEV distribution on the spatial plane for different periods of time reveal the existence of well-defined trends in the maxima. In the temporal plane, a presence of temporal cyclic components oscillating over a weak linear component with a negative slope is noticed, while in the spatial plane, a weak nonlinear local trend is present on a plane with a positive slope towards the west, covering the entire study area. An explicit spatial estimate of the 25-year return period revealed that the more extreme risk levels are located in the western region of the study area.

A study of the influence of tropospheric subsidence on spring and summer surface ozone concentrations at the JRC Ispra station in northern Italy

Abstract. The influence of tropospheric ozone on the surface ozone concentrations is investigated at the monitoring station of JRC Ispra, based on 10 years of measurements (2006–2015) of surface ozone data. In situ hourly measurements of ozone and other air pollutants, meteorological parameters, and weekly averaged 7Be (as an indicator of upper-tropospheric–stratospheric influence) and 210Pb measurements (as an indicator of boundary layer influence) have been used for the analysis. In addition, IASI + GOME-2 and IASI ozone satellite data have also been used. It is observed that frequently 7Be and ozone weekly peaks coincide, which might be explained by the impact of deep atmospheric subsidence on surface ozone, particularly during late spring and early summer. Based on this observation, a detailed analysis of selected 7Be and ozone episodes occurring during that period of the year has been performed in order to further elucidate the mechanisms of tropospheric influence on the surface pollutant concentrations. For the analysis, composite NOAA/ESRL reanalysis synoptic meteorological charts in the troposphere have been used as well as IASI satellite ozone measurements and NOAA HYSPLIT back trajectories. The JRC station hourly measurements during subsidence episodes show very low values of local pollution parameters (e.g., NOx, 222Rn, nephelometer data, PM10), close to zero. Conversely, during these periods ozone levels usually reach values around 45–60 ppb during the afternoon hours but also show significantly higher values than the average during the night and morning hours, which is a sign of direct tropospheric influence on the surface ozone concentrations.

Long-Term Variations of Air Quality Influenced by Surface Ozone in a Coastal Site in India: Association with Synoptic Meteorological Conditions with Model Simulations

Atmospheric ozone (O3) in the surface level plays a central role in determining air quality and atmospheric oxidizing capacity. In this paper, we review our comprehensive results of simultaneous measurements of surface ozone (O3) and its precursor gas (NOx) and weather parameters that were carried out continuously for a span of six years (January 2013–December 2018) at a typical rural coastal site, Kannur (11.9° N, 75.4° E) in South India. Surface O3 concentration reached its maximum during daytime hours and minimum during the night time. The influence of solar radiation and water content on variations of O3 are discussed. A Multi-Layer Perceptron (MLP) artificial neural network technique has been used to understand the effect of atmospheric temperature on the increase in O3 over the past six years. This has been found that temperature has been a major contributor to the increase in O3 levels over the years. The National Centre for Atmospheric Research- Master Mechanism (NCAR-MM) Photochemical box model study was conducted to validate the variations of O3 in different seasons and years, and the results were shown to be in good agreement with observed trends.

Neural Network Model Analysis for Investigation of NO Origin in a High Mountain Site

Measurements of nitrogen oxide (NO), ozone (O3), and meteorological parameters have been carried out between September and November 2013 in a high mountain site in Central Italy at the background station of Mt. Portella (2401 m a.s.l.). Three NO plumes, with concentrations up to about 10 ppb, characterized the time series. To investigate their origin, single hidden layer feedforward neural networks (FFNs) have been developed setting the NO as the output neuron. Five different simulations have been carried out maintaining the same FFNs architecture and varying the input nodes. To find the best simulations, the number of the neurons in the hidden layer varied between 1 and 40 and 30 trials models have been evaluated for each network. Using the correlation coefficient (R), the normalized mean square error (NMSE), the fractional bias (FB), the factor of 2 (FA2) and the t-student test, the FFNs results suggest that two of the three NO plumes are significantly better modeled when considering the dynamical variables (with the highest R of 0.7996) as FFNs input compare to the simulations that include as input only the photochemical indexes (with the lowest R of 0.3344). In the Mt. Portella station, transport plays a crucial role for the local NO level, as demonstrated by the back-trajectories; in fact, considering also the photochemical processes, the FFNs results suggest that transport, more than local sources or the photochemistry, can explain the observed NO plumes, as confirmed by all the statistical parameters.

Ozone Layer Evolution in the Early 20th Century

The ozone layer is well observed since the 1930s from the ground and, since the 1980s, by satellite-based instruments. The evolution of ozone in the past is important because of its dramatic influence on the biosphere and humans but has not been known for most of the time, except for some measurements of near-surface ozone since the end of the 19th century. This gap can be filled by either modeling or paleo reconstructions. Here, we address ozone layer evolution during the early 20th century. This period was very interesting due to a simultaneous increase in solar and anthropogenic activity, as well as an observed but not explained substantial global warming. For the study, we exploited the chemistry-climate model SOCOL-MPIOM driven by all known anthropogenic and natural forcing agents, as well as their combinations. We obtain a significant global scale increase in the total column ozone by up to 12 Dobson Units and an enhancement of about 20% of the near-surface ozone over the Northern Hemisphere. We conclude that the total column ozone changes during this period were mainly driven by enhanced solar ultra violet (UV) radiation, while near-surface ozone followed the evolution of anthropogenic ozone precursors. This finding can be used to constrain the solar forcing magnitude.

A Stratospheric Intrusion-Influenced Ozone Pollution Episode Associated with an Intense Horizontal-Trough Event

Ozone pollution is currently a serious issue in China. As an important source of tropospheric ozone, the stratospheric ozone has received less concern. This study uses a combination of ground-based ozone measurements, the latest ERA5 reanalysis data as well as chemistry-climate model and Lagrangian Particle Dispersion Modeling (LPDM) simulations to investigate the potential impacts of stratospheric intrusion (SI) on surface ozone pollution episodes in eastern China. Station-based observations indicate that severe ozone pollution occurred from 27 April to 28 April 2018 in eastern China, with maximal values over 140 ppbv. ERA5 meteorological and ozone data suggest that a strong horizontal-trough exists at the same time, which leads to an evident SI event and brings ozone-rich air from the stratosphere to the troposphere. Using a stratospheric ozone tracer defined by NCAR’s Community Atmosphere Model with Chemistry (CAM-Chem), we conclude that this SI event contributed about 15 ppbv (15%) to the surface ozone pollution episode during 27–28 April in eastern China. The potential impacts of SI events on surface ozone variations should be therefore considered in ozone forecast and control.

Coupled Stratospheric Chemistry–Meteorology Data Assimilation. Part I: Physical Background and Coupled Modeling Aspects

A coupled stratospheric chemistry–meteorology model was developed by combining the Canadian operational weather prediction model Global Environmental Multiscale (GEM) with a comprehensive stratospheric photochemistry model from the Belgian Assimilation System for Chemical ObsErvations (BASCOE). The coupled model was called GEM-BACH for GEM-Belgian Atmospheric CHemistry. The coupling was made across a chemical interface that preserves time-splitting while being modular, allowing GEM to run with or without chemistry. An evaluation of the coupling was performed by comparing the coupled model, refreshed by meteorological analyses every 6 h, against the standard offline chemical transport model (CTM) approach. Results show that the dynamical meteorological consistency between meteorological analysis times far outweighs the error created by the jump resulting from the meteorological analysis increments at regular time intervals, irrespective of whether a 3D-Var or 4D-Var meteorological analysis is used. Arguments in favor of using the same horizontal resolution for chemistry, meteorology, and meteorological and chemical analysis increments are also presented. GEM-BACH forecasts refreshed by meteorological analyses every 6 h were compared against independent measurements of temperature, long-lived species, ozone and water vapor. The comparison showed a relatively good agreement throughout the stratosphere except for an upper-level warm temperature bias and an ozone deficit of nearly 15%. In particular, the coupled model simulation during an ozone hole event gives better ozone concentrations than a 4D-Var chemical assimilation at a lower resolution.

An explicit study of local ozone budget and NOx-VOCs sensitivity in Shenzhen China

In China, a significant reduction in primary pollution has been observed due to the Clean Air Action since 2013, and ozone pollution has become increasingly prominent over the past years. Pearl River Delta (PRD) is one of the most successful regions concerning primary pollution control, while is suffering from severe ozone pollution during autumn. In this study, we present a field campaign in Shenzhen, a megacity in PRD, in October 2018 with measurements of ozone and photochemical precursors. These observational data are helpful to analyze the local ozone budget and its sensitivity to precursors with the help of an observation-based model (RACM2-LIM1). The observed ozone concentration was up to 121 ppbv during a photochemical episode from 1 to 8 October, when intensive ozone formation up to tens of ppbv/h was found. Ozone vertical measurement indicates the fast ozone production is happening throughout the planetary boundary layer (PBL), which is an important source of morning ozone increase resulting in ozone pollution. An explicit case study is performed to reveal the diurnal feature of instantaneous ozone production rate (P(Ox)) and accumulative P(Ox) based on the O3-NOx-VOC sensitivity, ROx radical primary production rate (P (ROx)), and LN/Q for three cases including ozone pollution and attainment periods. Results show that nitrogen oxides (NOx = NO + NO2) reduction have positive and negative impact on local ozone production from one pollution episode to the other, which indicates the complexity of O3-precursors sensitivity and difficulty to control ozone pollution in Shenzhen. Finally, comparison among measurements in other campaigns provides additional evidence on local ozone production sensitivity on NOx and anthropogenic volatile organic compounds (AVOCs) with respect to a temporal and spatial change. The NOx reduction in Shenzhen has led to higher ozone production from 2015 to 2018 given the nearly constant VOC. However, the ozone mitigation would be benefit from further NOx reduction in the conditions of 2018.

The effect of considering polar vortex dynamics in the validation of satellite total ozone observations

The main aim of this paper is to demonstrate the magnitude in which validation results of space-based total ozone column, TOC, measurements are affected by the location of the polar vortex. Potential Vorticity is used as an indicator to determine the polar vortex's boundary and surface area, provided by ERA-Interim reanalysis datasets from the European Centre for Medium-Range Weather Forecasts (ECMWF). The total ozone measurements that were examined fall within the hemispherical winter-spring period, focusing on middle and high latitudes on both hemispheres. The space-based total ozone data produced by the GODFIT (GOME-type Direct FITting) v4 algorithm as applied to the OMI/Aura, GOME-2/Metop-A and Metop-B observations, part of the European Space Agency's Ozone Climate Change Initiative project, are compared to TOC measurements from Brewer and Dobson spectrophotometers archived at the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) repository. The satellite-to-ground collocations were classified depending on whether both satellite and ground-based measurements are inside or outside the polar vortex (matched) or one measurement is inside whereas the other one is outside the polar vortex (mismatched). It is shown that the matched cases present an improved agreement between satellite and ground TOC measurements compared to the mismatched cases. Considering all examined stations for GOME2-A, GOME2-B, and OMI, the mean bias for the mismatched cases was found to be 2.22 ± 0.4%, 1.84 ± 0.57%, and 1.93 ± 0.39% respectively, while for the matched cases was found to be 1.46 ± 0.17%, 1.69 ± 0.22%, 1.7 ± 0.19% respectively. For the three satellite sensors, the mismatched cases do not exceed 3.3% of the total available collocations per station during the winter-spring period between years 2007 and 2017, where applicable. Hence, on a global scale, the exclusion of mismatched collocated measurements does not cause significant changes and the resulting impact on the validation of the satellite TOCs is small. However, when considering single stations consistently affected by the polar vortex, we conclude that mismatched cases should be excluded from the comparisons.

Surface mesovortices in relation to the urban heat island effect over the Saint Louis metropolitan area

Using high spatial and temporal resolution mesonet data, a comprehensive surface mesoanalysis of Saint Louis's Urban Heat Island (UHI) effect was conducted. The synoptic and mesoscale conditions were evaluated in which the surface mesovortices were observed. A long-term analysis of the surface mesovorices and four cases are presented as well as a hypothesis developed to explain the formation of the surface mesovortices.Results suggest that surface mesovortices were often observed in conjunction with UHI events and low wind speeds within the Saint Louis metropolitan area. The surface mesovortices are caused in part by the direct thermal circulation produced by the UHI enhancing existing vorticity.The surface mesovortices are also hypothesized to have impact on local air quality; surface ozone measurements at Saint Louis Science Center were noticed to spike during one surface mesovortex event. The surface mesovortices may re-circulate ozone created outside the immediate Saint Louis metropolitan area back into the immediate Saint Louis metropolitan area.

Assessment, Selection and Demonstration of Technologies and Equipment for Measuring Welder Exposure to Ozone during GMAW (MIG Welding) on Aluminum Alloys

Ozone is a by-product of arc welding on aluminum alloys and stainless steels. Assessment of exposure is difficult because emissions are short in duration and large in magnitude compared to background levels, and generally occur unpredictably during work activity. The welding environment is particularly harsh. This study applied a systematic process to identify technologies and sampling devices available in the marketplace and to select suitable candidates and reject unsuitable ones. Candidates suitable for study included colorimetric detector tubes, an Ultra-Violet (UV) air pollution analyzer, and person-portable instruments, one containing a heated semi-conductor sensor and the other an electrochemical sensor. These devices were exposed to welding plumes contained in a pre-conditioned plastic bag and to unconfined plumes during production welding (Gas Metal Arc Welding [GMAW] commonly known as Metal Inert Gas [MIG welding]) on aluminum alloys. Nitrogen dioxide is an interferent in the assessment of ozone exposure by almost all technologies. Particulates and unreacted metal atoms in the plume further complicate measurement of ozone. None of the measurement technologies overwhelmed the others in this application. The harshness of the welding environment eliminated several candidates. Colorimetric detector tubes provided the best compromise between performance and safety in proof-of-concept testing on welders.

Very high stratospheric influence observed in the free troposphere over the northern Alps – just a local phenomenon?

Abstract. The atmospheric composition is strongly influenced by a change in atmospheric dynamics, which is potentially related to climate change. A prominent example is the doubling of the stratospheric ozone component at the Zugspitze summit station (2962 m a.s.l., Garmisch-Partenkirchen, Germany) between the mid-seventies and 2005, roughly from 11 to 23 ppb (43 %). Systematic efforts for identifying and quantifying this influence have been made since the late 1990s. Meanwhile, routine lidar measurements of ozone and water vapour carried out at Garmisch-Partenkirchen (German Alps) since 2007, combined with in situ and radiosonde data and trajectory calculations, have revealed that stratospheric intrusion layers are present on 84 % of the yearly measurement days. At Alpine summit stations the frequency of intrusions exhibits a seasonal cycle with a pronounced summer minimum that is reproduced by the lidar measurements. The summer minimum disappears if one looks at the free troposphere as a whole. The mid- and upper-tropospheric intrusion layers seem to be dominated by very long descent on up to hemispheric scale in an altitude range starting at about 4.5 km a.s.l. Without interfering air flows, these layers remain very dry, typically with RH ≤5 % at the centre of the intrusion. Pronounced ozone maxima observed above Garmisch-Partenkirchen have been mostly related to a stratospheric origin rather than to long-range transport from remote boundary layers. Our findings and results for other latitudes seem to support the idea of a rather high contribution of ozone import from the stratosphere to tropospheric ozone.

Measurement of ozone produced by 10 MeV electron accelerator Yazd in various currents

In this study, the concentration of ozone gas in various currents which arises by 10 MeV electron beam of RHODOTRON TT200 electron accelerator (Belgium) in the Radiation Application Research School (Yazd, Iran) was measured and studied continuously. All experiments were measured at the normal temperature (25̂C) and normal pressure (1 ATM) under normal working conditions of the electron accelerator, while accelerator's ozone fans were operating. For the accurate measurement, ozone gas is transmitted through a gas pump and polymer pipes. While so far, online measurement of ozone gas has not been measured in various currents of the electron accelerator (RHODOTRON TT200). The purpose of this study is the continuous measurement of ozone gas in various currents from 0.5 mA to 3 mA of RHODOTRON TT200, via three methods (Iodometry, UV-Visible, Portable Monitor-Series 500) and then the results of the measurements in different methods are evaluated with each other.

The importance of ground-based and satellite observations for monitoring and estimation of UV radiation in Novi Sad (Serbia)

Solar ultraviolet (UV) radiation is a significant health hazard in the warm part of the year. In order to assess the level of hazard and the effects of UV radiation on the living world, long-term measured or estimated data are needed. In Novi Sad, the measurement of UV radiation has been performed since 2003, while ozone measurements have been made since 2007. However, those data sets are too short for assessing long-term biological effects. Therefore, several techniques for reconstruction of UV radiation doses have been developed. Reconstruction techniques are based on using available ground-based measurements of the meteorological data and satellite measurements of the total ozone column. It is shown that techniques that use ozone data show better performance than those that use only ground-based meteorological measurements. However, the difference between the performances of the methods is smaller when it comes to the monthly values, indicating that the techniques which use only ground-based meteorological measurements are roughly as good as the ozone-based techniques for assessing long-term changes in the surface UV radiation. The statistically significant increasing long term-trend of annual mean erythemal UV doses (ERY) and the decreasing trend in the total ozone column in Novi Sad since 1981 have been noticed. An increase in ERY has been noticed in all the seasons except in autumn and it is the highest in winter. The analysis showed that the increase in the ERY in the period 1981–1996 was mainly caused by the total ozone column, while the increase after 1996 is largely caused by cloudiness.

Nitrogen Dioxide and Ozone Pollution in the Chicago Metropolitan Area

Ground-level ozone is a harmful air pollutant associated with several health issues. Ozone concentrations have exceeded the National Ambient Air Quality Standards (NAAQS) in the Chicago metropolitan area on hot summer days for many years because of nitrogen oxide and volatile organic compound emissions. Annual fourth highest 8-hour ozone concentrations have been between 0.070 and 0.084 ppm at several monitoring sites in Cook county, during the 2016-2018 time period. The continuous measurement of nitrogen dioxide (NO2) and ozone (O3) was conducted in several communities in Chicago in 2017. The air pollution impacts the health of all who live in the area. The data were used to analyze correlations between the O3 distribution and its association with ambient concentrations of NO2 from transportation emissions. Higher concentrations in NO2 and O3 occurred in succession in the daytime. The diurnal variation of O3 concentration was analyzed. The daily cycle of NO2 concentration reaches a maximum in the late morning and has smaller nighttime concentrations. The daily cycle of ozone concentration reaches the maximum in the afternoon and also becomes smaller for nighttime concentrations. In addition, relationships were found between O3 and NO2. Monthly variations of ozone and NO2 are presented. Some options to reduce ozone pollution are presented.

Long-term changes of regional ozone in China: implications for human health and ecosystem impacts

The first Tropospheric Ozone Assessment Report (TOAR) provides information on present-day distributions and long-term trends of ozone metrics relevant for climate change, human health, and vegetation. However, only few results are available in TOAR for China due to limited long-term ozone observations. Here, we present an integrated analysis of long-term measurements of surface ozone from eight sites distributed in the North China Plain (NCP) and Yangtze River Delta (YRD), the relatively underdeveloped region Northeast China, and the remote regions in Northwest and Southwest China. Trends and present-day values for seven annual and five seasonal ozone metrics were calculated following the TOAR methodologies. We compare the seasonal and diurnal cycles of ozone concentrations as well as the present-day values of ozone among sites and discuss the long-term trends in the ozone metrics. Large and significant increases of ozone are detected at the background site in the NCP, moderate increases at the global baseline site in western China, significant decreases at the northwestern edge of China, and nearly no trend at other sites. Extremely high values of ozone occurred in the NCP and YRD, particularly in warmer seasons. The present-day levels of summer ozone metrics in the NCP are much higher than the thresholds set in TOAR for the highest value groups of ozone metrics. The summer ozone metrics at the Shangdianzi background site in the NCP indicate increases at rates of more than 2%/yr during 2004–2016. In contrast, ozone at the Lin’an background site in the YRD was constant over the period 2006–2016. Our results fill some knowledge gaps in spatiotemporal changes of ozone in China and may be of useful in the assessment of ozone impacts on human health and vegetation.

Ozone Lidar Observations in the City of Paris: Seasonal Variability and Role of The Nocturnal Low Level Jet

Ozone lidar measurements have been carried out in Paris during 4 years to characterize the seasonal variability of the vertical gradient within the urban planetary boundary layer (PBL). The interaction between NOx emission and thermal stability of the PBL is the main driver of the winter strong positive O3 gradient, while summer neutral gradient is related to weaker thermal stability and photochemical ozone production at the regional scale. Simultaneous lidar measurements of ozone and wind vertical profiles during 36 hours in September 2014 also show that the nocturnal low level jet (NLLJ) plays a significant role in the early morning ozone increase.