Measurements Of O3 Research Articles

Ozone Production in the Soberanes Smoke Haze: Implications for Air Quality in the San Joaquin Valley During the California Baseline Ozone Transport Study

AbstractThe Soberanes Fire burned 53,470 ha (132,127 acres) along the central California coast between 22 July and 12 October 2016, generating dense smoke and a variety of gaseous compounds that drifted eastward into the San Joaquin Valley Air Basin (SJVAB), an “extreme” nonattainment area for ozone (O3). These gases included nitrogen oxides (NOx) and volatile organic compounds, the photochemical precursors of O3. The fire started during the California Baseline Ozone Transport Study, a field campaign that brought aircraft, surface, and remote sensing measurements of O3 and related species to central California. In this paper, we use the California Baseline Ozone Transport Study measurements to assess the impact of the Soberanes Fire on ozone and particulate air quality in the SJVAB. We focus our analysis on 27 July to 2 August when the smoke haze was heaviest and the highest O3 concentrations in the SJVAB during 2016 were recorded. Our analyses suggest that while 40 to 60 ppbv of fire‐generated O3 was transported to the eastern SJVAB in the 1‐ to 3‐km‐altitude range, relatively little smoke or fire‐generated O3 reached the surface in the Visalia area.

First observation-based study on surface O3 trend in Indo-Gangetic Plain: Assessment of its impact on crop yield

Tropospheric ozone (O3) is an important air pollutant which causes substantial losses in crop production. Increasing O3 levels in India particularly in Indo-Gangetic Plain (IGP) is a major issue as it is reducing the crop yield. The present study is an attempt to determine the O3 and its precursor trend using continuous ground-based observations at a suburban site in IGP. The study focuses on the overall characteristics of annual, monthly, diurnal and hourly measurements of O3. Annual mean values of O3 have shown an increment of 19.2% from 2010 to 2015. Similarly, nitrogen oxide (NOx) levels increased by 30.2%. O3 levels at the study site showed a significant increasing trend of 0.7 ppb/yr. The observed O3 trend was analyzed in terms of changes in NOx levels and meteorological parameters. No significant difference in meteorological parameters was observed during 2010–15, however, NOx levels have shown an increasing trend of 0.9 ppb/yr. Further to quantify the impact of increasing O3 on crops, ozone-related crop yield losses for rice and wheat crop were determined for the period 2010–15. AOT40 (accumulated ozone exposure over a threshold of 40 ppb) and M7 (mean 7-h O3 mixing ratio from 09:00 to 15:59 LT) O3 exposure metrics were used to calculate the reduction in crop yield during major crop growing seasons: Rabi and Kharif.

Simultaneous detection of ozone and nitrogen dioxide by oxygen anion chemical ionization mass spectrometry: a fast-time-response sensor suitable for eddy covariance measurements

Abstract. We report on the development, characterization, and field deployment of a fast-time-response sensor for measuring ozone (O3) and nitrogen dioxide (NO2) concentrations utilizing chemical ionization time-of-flight mass spectrometry (CI-ToFMS) with oxygen anion (O2-) reagent ion chemistry. We demonstrate that the oxygen anion chemical ionization mass spectrometer (Ox-CIMS) is highly sensitive to both O3 (180 counts s−1 pptv−1) and NO2 (97 counts s−1 pptv−1), corresponding to detection limits (3σ, 1 s averages) of 13 and 9.9 pptv, respectively. In both cases, the detection threshold is limited by the magnitude and variability in the background determination. The short-term precision (1 s averages) is better than 0.3 % at 10 ppbv O3 and 4 % at 10 pptv NO2. We demonstrate that the sensitivity of the O3 measurement to fluctuations in ambient water vapor and carbon dioxide is negligible for typical conditions encountered in the troposphere. The application of the Ox-CIMS to the measurement of O3 vertical fluxes over the coastal ocean, via eddy covariance (EC), was tested during the summer of 2018 at Scripps Pier, La Jolla, CA. The observed mean ozone deposition velocity (vd(O3)) was 0.013 cm s−1 with a campaign ensemble limit of detection (LOD) of 0.0027 cm s−1 at the 95 % confidence level, from each 27 min sampling period LOD. The campaign mean and 1 standard deviation range of O3 mixing ratios was 41.2±10.1 ppbv. Several fast ozone titration events from local NO emissions were sampled where unit conversion of O3 to NO2 was observed, highlighting instrument utility as a total odd-oxygen (Ox=O3+NO2) sensor. The demonstrated precision, sensitivity, and time resolution of this instrument highlight its potential for direct measurements of O3 ocean–atmosphere and biosphere–atmosphere exchange from both stationary and mobile sampling platforms.

Breathing-rate adjusted population exposure to ozone and its oxidation products in 333 cities in China

While PM2.5 (particles with aerodynamic diameter less than 2.5 µm) concentrations in China are beginning to decline because of pollution abatement measures, ozone (O3) concentrations continue to rise. In this study, we have used a Monte Carlo approach to estimate breathing-rate adjusted (BRA) population exposure to ozone and its oxidation products based on hourly O3 measurements collected in 2017 from monitoring stations in 333 Chinese cities. The median measured outdoor O3 concentration in these cities was 31 ppb, while the median calculated indoor concentrations of ozone and ozone-derived oxidation products were 7.5 ppb and 21 ppb, respectively. The median BRA O3 exposure concentration was 12 ppb, ranging from 2.2 ppb to 18 ppb among the cities. Eastern and central cities had higher exposure concentrations, while northeastern and western cities had lower. On average, the residents of these cities spent 88% of their time indoors. Consequently, even with breathing rate adjustments, indoor O3 exposure averaged 50% of the total O3 exposure nationwide. The median BRA exposure concentration for ozone-derived products was 18 ppb, ranging from 4.5 ppb to 32 ppb among the cities. On average, BRA exposure concentrations were 1.6 times larger for oxidation products than for ozone, while seasonal variations of exposure concentrations were smaller for oxidation products than for ozone. As many of the products of indoor ozone chemistry are toxic, the health consequences of exposure to such products should be further investigated.

Performance evaluation of ozone and particulate matter sensors

ABSTRACTAs public awareness and concern about air quality grows, companies and researchers have begun to develop small, low-cost sensors to measure local air quality. These sensors have been used in citizen science projects, in distributed networks within cities, and in combination with public health studies on asthma and other air-quality-associated diseases. However, sensor long-term performance under different environmental conditions and pollutant levels is not fully understood. In addition, further evaluation is needed for other long-term performance trends such as performance among sensors of the same model, comparison between sensors from different companies and comparison of sensor data to federal equivalence or reference method (FEM/FRM) measurements. A 10-month evaluation of two popular particulate matter (PM) sensors, Dylos DC1100 and AirBeam, and a popular ozone (O3) sensor, Aeroqual 500, was performed as part of this study. Data from these sensors were compared to each other and to FEM/FRM data and local meteorology. The study took place at the Houston Regional Monitoring (HRM) site 3, located between the Houston Ship Channel and Houston’s urban center. PM sensor performance was found to vary in time, with multivariate analysis, binning of data by meteorological parameter, and machine learning techniques able to account for some but not all performance variations. PM type (i.e., size distribution, fiber-flake-spheroid shape and black-brown-white color) likely played a role in the changing sensor performance. Triplicate individual Aeroqual O3 sensors tracked reasonably well with the FEM data for most of the measurement period but had irregular periods of O3 measurement offset. While the FEM data indicated 4 days where ozone levels were above the NAAQS, the Aeroqual ozone sensors indicated a substantially higher number of days, ranging from 9 to 16 for the three sensors.Implications: This paper evaluated the long-term performance of several commercial low-cost sensors (PM2.5 and ozone) as compared to federal equivalence method (FEM) monitors under a range of meteorological and air quality conditions. PM2.5 sensors performed well on low humidity days with winds indicative of sea salt or dust PM sources but had poor correlation with FEM data under other conditions. Two types of PM sensors were studied (Dylos 1100 and AirBeam) and data only correlated well between sensors of the same type. Sensor networks with multiple PM sensor types would not be as useful for comparative purposes as sensor networks of the same type. Relative humidity corrections alone did not increase sensor agreement with FEM to acceptable levels, specific information about PM sources and sensor response in the area measured is needed. Low-cost ozone sensors tested (Aeroqual) performed well but were biased high and overestimated days above ozone NAAQS.

Quantifying Influences of Nocturnal Mixing on Air Quality Using Atmospheric Radon Measurement-Case Study in Jinhua City, China

ABSTRACT The atmospheric mixing state and emission rates play decisive roles in public exposure to urban air pollution. This study utilizes atmospheric radon measurements taken with the SM200 “stability monitor,” which reflect changes in the atmospheric mixing state, to evaluate and forecast air quality. Using six months (March–August 2016) of atmospheric radon measurements in Jinhua, China, we classify the nocturnal atmospheric stability conditions into four distinct categories, “well-mixed”, “weakly stable”, “moderately stable”, and “most stable”, by applying a modified radon-based stability technique. We calculate the atmospheric self-cleaning ability index (ASI) and evaluate it with the four-category stability scheme, and the results confirm that the atmospheric radon measurements reliably represent the atmospheric mixing state. Analyzing PM2.5, PM10, SO2, NO2, CO, and O3 measurements from three nearby stations during the campaign, we find that the pollutant concentrations and air quality index (AQI) values assigned using the aforementioned stability scheme are consistent with the defined atmospheric mixing states. We subsequently demonstrate that the modified radon-based stability method is suitable for targeting the most unfavorable air quality conditions and determining where the emissions originated. Finally, we propose a simple ASI-based model for predicting regional severe air pollution.

Enhanced NO2 and aerosol extinction observed in the tropospheric column behind lake-breeze fronts using MAX-DOAS

Abstract The lake breezes that frequently occur in Southern Ontario impact the levels of pollutants experienced by the populations in urban areas. The effects of lake breeze circulations on pollution transport and processing are not well understood. Few studies have measured the circulations’ impact on pollutants both at the surface and within the tropospheric column. In this study, pollutants in the tropospheric column (NO2 VCDs and AODs) were measured using MAX-DOAS concurrent with near-surface measurements of NOx, O3, and PM2.5 on lake breeze days in Toronto in September and October. The arrival of lake-breeze fronts (LBF) was identified using co-located meteorological data. The presence of lake breezes was confirmed using mesoscale analyses of radar, satellite and a network of meteorological stations. NO2 VCDs exhibited short-term increases of 0.8-3.4×1016 molecules cm-2 above the pre-LBF levels following the arrival of a LBF. These measurements are the first confirmation of the theorized presence of enhanced total burden of pollution within the total column behind the front within a lake-breeze circulation on multiple lake breeze days. Rapid decreases of O3 of up to 13 ppb at the arrival of the lake-breeze front were unexpected based on observed increases in O3 in other studies, but can be attributed to reduced photochemical O3 production during late summer and fall compared to mid-summer. AODs exhibited delayed enhancements compared to NO2 VCDs, appearing to be driven by enhanced humidity following the front, in addition to enhanced particle concentration. Our measurements highlight the complex 3-D structure of lake-breeze circulations.

A Comparison Study of Indoor and Outdoor Air Quality in Nanjing, China

ABSTRACT Because humans spend much of their time in indoor microenvironments, the air quality indoors has attracted significant attention. This study simultaneously conducted real-time indoor observations and comprehensive outdoor measurements of O3, CO and PM2.5 in suburban Nanjing in eastern China from September to December 2018. The O3, CO and PM2.5 exhibited median indoor concentrations of 3.2 ppb, 395.8 ppb and 17.3 µg m–3, respectively, based on measurements in a room with closed windows and relatively regular daily indoor human activity, and median outdoor values of 30.5 ppb, 386.1 ppb and 37.2 µg m–3, resulting in median indoor-outdoor (I/O) ratios of 0.14, 1.01 and 0.46. Moreover, the indoor concentrations traced the outdoor variations with correlations of approximately 0.68, 0.82 and 0.82 for the O3, CO and PM2.5, respectively. During pollution episodes, the indoor O3 and PM2.5 concentrations reached about 30 ppb and 130 µg m–3, respectively. Both meteorological conditions (e.g., wind speed or relative humidity) and human activity indoors influenced the relationships between the indoor and outdoor concentrations, including the I/O ratios and time lag. A simplified indoor-outdoor mass-balance equation was developed to simulate the indoor concentrations, and the predictions fitted the observed data for most of the testing period, especially after considering the human activity indoors and limited penetration of particles. This study enhances our understanding of the indoor-outdoor relationships for gaseous and particulate matter concentrations in polluted areas such as the Yangtze River Delta and highlights the urgent need for improving indoor air quality in the megacities of China.

Long-term exposure to ozone and children's respiratory health: Results from the RESPOZE study

BackgroundAlthough there is evidence on the effects of short-term ozone (O3) exposures on children's respiratory health, few studies have reported results on the effects of long-term exposures. We report the effects of long-term exposure to O3 on respiratory health outcomes in 10–11-year old children. MethodsWe conducted a panel study in a sample of the general population of school children in two cities with high average O3 concentrations, Athens and Thessaloniki, Greece. All 186 participating students were followed up intensively for 5 weeks spreading across a school year. Data was collected through questionnaires, weekly personal O3 measurements, spirometry, FeNO and time-activity diaries. Long-term O3 exposure was assessed using fixed site measurements and modeling, calibrated for personal exposures. The associations between measured lung function parameters and lung function growth over the study period, as well as FeNO and the occurrence of symptoms with long-term O3 exposure were assessed through the application of multiple mixed effects 2-level regression models, adjusting for confounders and for short-term exposures. ResultsA 10 μg/m3 increase in calibrated long-term O3exposure, using measurements from fixed site monitors was associated with lower FVC and FEV1 by 17 mL (95% Confidence Interval: 5–28) and 13 mL (3–21) respectively and small decreases in lung growth: 0.008% (0.002–0.014%) for FVC and 0.006% (0.000–0.012%) in FEV1 over the study period. No association was observed with PEF, FeNO or the occurrence of symptoms. A similar pattern was observed when the exposure estimates from the dispersion models were employed. ConclusionsOur study provides evidence that long-term O3 exposure is associated with reduced lung volumes and growth.

Red Flag for Arterial Damage? Early Evidence of a Potential Connection with Ozone.

Red Flag for Arterial Damage? Early Evidence of a Potential Connection with Ozone.

Large regional differences of soil water limitation effect on ozone induced yield loss for wheat and potato in Switzerland

The accumulated stomatal ozone (O3) uptake over a threshold (Phytotoxic Ozone Dose POD6), calculated by an ozone deposition model, has been shown to be the most appropriate metric to quantify negative effects of O3 on food crops. In this study we used data of 13 sites in different regions of Switzerland with multiple years of O3 measurements to quantify the stomatal O3 uptake and the related yield loss of wheat and potato. Flux patterns for different years were calculated with the DO3SE model to disentangle the influence of contrasting seasonal environmental conditions. Regional and inter-annual differences in meteorological conditions led to considerable variations in soil water conditions and the POD6 values for wheat. Potato stomatal uptake was much less influenced by soil water and showed a more even distribution of POD6 values across sites and years. The estimated nationally and temporally average yield loss was 3.2 ± 1.2% for wheat and 2.4 ± 0.8% for potato, calculated based on an area weighting.It was found that soil water deficit, observed frequently in the western part of Switzerland, had a large attenuation effect on stomatal O3 uptake by wheat and on corresponding yield losses. This highlights the importance of including soil moisture limitation in O3 uptake modelling even in moist climatic regions. The comparison of modelled evapotranspiration with water flux measurements over a wheat field showed a reasonable agreement concerning the temporal pattern and the magnitude. But it is also concluded that the DO3SE soil moisture module will need further testing and adaptation to improve accuracy of the model in dryer conditions.

An Ozone “Pool” in South China: Investigations on Atmospheric Dynamics and Photochemical Processes Over the Pearl River Estuary

AbstractPearl River Estuary (PRE) has been recognized as one of the key areas in South China experiencing severe air pollution. To understand the photochemical pollution over PRE, intensive measurements of O3 and its precursors were simultaneously conducted at a suburban site on the east bank of PRE (Tung Chung, TC) in Hong Kong and a rural site on the west bank (Qi'ao Island, QAI) in Zhuhai from 25 September to 29 November 2016. Three and sixteen O3 episode days (days with the maximum hourly O3 higher than 100 ppbv) were captured at TC and QAI, respectively. On the three days when O3 episodes occurred at TC, QAI also suffered from O3 episodes, which were all associated with tropical cyclones (typhoons). As a downwind site of PRE when northwesterly winds prevailed, TC displayed a higher maximum hourly O3 than QAI on these three days. In contrast, the other thirteen episodes that solely occurred at QAI were generally under northeasterly winds, which brought more coastal air to TC and led to lower levels of O3 at this site. In addition, the stronger titration of the locally emitted NO to O3 also accounted for the lower O3 at TC on these days. The simulations by Weather Research and Forecasting coupled with Chemistry model indicated that the interactions of synoptic winds and mesoscale breezes led to relatively weak winds and long residence time for air pollutants over the PRE, thereby air pollution accumulation. This provided the likelihood of intensive chemical productions of O3 over PRE, with the production rates even higher than those in the surrounding land areas. As such, it was concluded that PRE was a “pool” of O3, where atmospheric dynamics caused the accumulation of air pollutants and subsequently intensive photochemical reactions. The findings in this study may also apply to the other estuaries connecting terrestrial and marine systems over the world.

Indoor Photochemistry Involving Ozone in Rural Location of Kannur−A Tropical Site in India

This study reports the indoor ozone (O3) pollution in the rural location of Kannur, a tropical site in India, during March 2018 and the influence of their most important determinants. Measurements of indoor O3, NO, NO2 and NOx were carried out in a residential building for a period of one week. Measurements were taken from the kitchen, as it had been identified as the most polluted spot. The background concentrations of O3, NO, NO2 and NOx were also monitored. Indoor O3 originates mainly from the outdoor environment and is also produced from indoor sources. The results show that there is a higher level of indoor O3 during cooking hours. The study indicated that cooking activities in the kitchen had a strong impact on the indoor O3 level. Ozone is an important gaseous pollutant which may lead to severe health problems such as decreased lung function and respiratory symptoms.

Alleviated systemic oxidative stress effects of combined atmospheric oxidant capacity by fish oil supplementation: A randomized, double-blinded, placebo-controlled trial

BackgroundCombined atmospheric oxidant capacity (Ox), represented by the sum of nitrogen dioxide (NO2) and ozone (O3), is an important hazardous property of outdoor air pollution mixture. It remains unknown whether its adverse effects can be ameliorated by dietary fish-oil supplementation. ObjectiveTo assess the effects of fish-oil supplementation against oxidative stress induced by acute Ox exposure. MethodsWe conducted a randomized, double-blinded and placebo-controlled study among 65 young adults in Shanghai, China between September 2017 and January 2018. We randomly assigned participants to receive either 2.5 g/day of fish oil or placebo, and conducted four repeated physical examinations during the last two months of treatments. Ox concentrations were calculated as the sum of hourly measurements of NO2 and O3. We measured six biomarkers on systemic oxidative stress and antioxidant activity. Linear mixed-effect models were used to assess the short-term effects of Ox on biomarkers in each group. ResultsDuring our study period, the 72-h average Ox concentration was 93.6 μg/m3. Short-term exposure to Ox led to weaker changes in all biomarkers in the fish oil group than in the placebo group. Compared with the placebo group, for a 10-μg/m3 increase in Ox, there were smaller decrements in myeloperoxidase (MPO, difference = 5.92%, lag = 0–2 d, p = 0.03) and malondialdehyde (MDA, difference = 5.00%, lag = 1 d, p = 0.04) in the fish-oil group; there were also larger increments in total antioxidant capacity (TAC, difference = 16.33%, lag = 2 d, p = 0.02) and in glutathione peroxidase (GSH-Px, difference = 8.89%, lag = 0–2 d, p = 0.03) in the fish-oil group. The estimated differences for MPO were robust to adjustment for all co-pollutants and the differences for other biomarkers remained for some co-pollutants. ConclusionsThis trial provides first-hand evidence that dietary fish-oil supplementation may alleviate the systemic oxidative stress induced by Ox.

Investigation of Power Transmission of a Helium Plasma Jet to Different Dielectric Targets Considering Operating Modes

The interaction of an atmospheric pressure plasma jet with different dielectric surfaces is investigated using a setup of two ring electrodes around a ceramic capillary. In this study, in addition to electrical measurement methods such as the determination of voltage and current, special emphasis was placed on the power measurements at the electrodes and the effluent. The power dissipation is correlated with Fourier-transform infrared (FTIR) absorption spectroscopy measurements of O3 and NO2 densities. The results show the correlation between the dielectric constant and the dissipated power at the target. The ratio between power dissipation at the grounded ring electrode and the grounded surface shows an increase with increasing dielectric constant of the target. A correlation of the results with bacteria, tissue and water as envisaged dielectric targets shows four times the power dissipation at the treatment spot between bacteria and tissue.

Association of Estimated Long-term Exposure to Air Pollution and Traffic Proximity With a Marker for Coronary Atherosclerosis in a Nationwide Study in China

Epidemiologic evidence of the mechanisms of the association between long-term exposure to air pollution and coronary heart disease (CHD) is limited and relies heavily on studies performed in Europe and the United States, where air pollution levels are relatively low. In particular, the association between air pollution and CHD in patients with underlying risks for CHD is understudied. To determine whether air pollution and proximity to traffic are associated with the coronary artery calcium (CAC) score, a key atherosclerotic marker. In this prospective, population-based cross-sectional study in a large-scale setting in China, 8867 consecutive patients aged 25 to 92 years with suspected CHD were recruited between November 17, 2015, and September 13, 2017. Participants were excluded if they had previous myocardial infarction, stenting, or coronary artery bypass grafting or incomplete risk factors and exposure data. Each participant underwent assessment of CAC and CHD risk factors at baseline. Data were analyzed from December 2017 to November 2018. Annual means of fine particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5), nitrogen dioxide (NO2), and ozone (O3) were estimated at the participants' residences using a validated geostatistical prediction model. Exposure to a nearby roadway was also estimated. Computed tomography measurement of CAC score. The mean (SD) age of the 8867 participants was 56.9 (10.4) years; 4378 (53.6%) were men. Annual mean (SD) PM2.5, NO2, and O3 measurements were 70.1 (20.0), 41.4 (14.7), and 93.9 (10.5) μg/m3, respectively. The mean (SD) CAC score was 91.4 (322.2) Agatston units. Exposure to PM2.5 and NO2, adjusting for CHD risk factors and multiple pollutants, were independently associated with increases in CAC scores of 27.2% (95% CI, 10.8% to 46.1%) per 30 μg/m3 PM2.5 and 24.5% (95% CI, 3.6% to 49.7%) per 20 μg/m3 NO2. For PM2.5, odds of both detectable CAC (Agatston score >0; odds ratio, 1.28; 95% CI, 1.13 to 1.45) and severe CAC (Agatston score >400; odds ratio, 1.59; 95% CI, 1.20 to 2.12) were increased. Associations of CAC with PM2.5 and NO2 were greater among male participants (PM2.5: 42.2%; 95% CI, 24.3% to 62.7%; NO2: 45.7%; 95% CI, 25.3% to 69.5%) and elderly participants (PM2.5: 50.1%; 95% CI, 28.8% to 75.0%; NO2: 55.5%; 95% CI, 31.8% to 83.6%) and those with diabetes (PM2.5: 62.2%; 95% CI, 30.9% to 101.0%; NO2: 31.2%; 95% CI, 13.9% to 51.0%). Independent association with CAC score was 9.0% (95% CI, -1.4% to 20.4%) for O3 per 15 μg/m3 and 2.4% (95% CI, -0.6% to 5.4%) for distance near roadway per 50% decrease. In this large Chinese study, long-term exposures to PM2.5 and NO2 were independently associated with severity of CAC. This finding may provide support for the pathophysiological role of coronary atherosclerosis through which air pollution exposure may be associated with CHD.

Unusual chlorine partitioning in the 2015/16 Arctic winter lowermost stratosphere: observations and simulations

Abstract. The Arctic winter 2015/16 was characterized by cold stratospheric temperatures. Here we present a comprehensive view of the temporal evolution of chlorine in the lowermost stratosphere over the course of the studied winter. We utilize two-dimensional vertical cross sections of ozone (O3) and chlorine nitrate (ClONO2), measured by the airborne limb imager GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) during the POLSTRACC/GW-LCYCLE II/GWEX/SALSA campaigns, to investigate the tropopause region in detail. Observations from three long-distance flights in January, February, and March 2016 are discussed. ClONO2 volume mixing ratios up to 1100 pptv were measured at 380 K potential temperature in mesoscale structures. Similar mesoscale structures are also visible in O3 measurements. Both trace gas measurements are applied to evaluate simulation results from the chemistry transport model CLaMS (Chemical Lagrangian Model of the Stratosphere) and the chemistry–climate model EMAC (ECHAM5/MESSy Atmospheric Chemistry). These comparisons show agreement within the expected performance of these models. Satellite measurements from Aura/MLS (Microwave Limb Sounder) and SCISAT/ACE-FTS (Atmospheric Chemistry Experiment – Fourier Transform Spectrometer) provide an overview over the whole winter and information about the stratospheric situation above the flight altitude. Time series of these satellite measurements reveal unusually low hydrochloric acid (HCl) and ClONO2 at 380 K from the beginning of January to the end of February 2016, while chlorine monoxide (ClO) is strongly enhanced. In March 2016, unusually rapid chlorine deactivation into HCl is observed instead of deactivation into ClONO2, the more typical pathway for deactivation in the Arctic. Chlorine deactivation observed in the satellite time series is well reproduced by CLaMS. Sensitivity simulations with CLaMS demonstrate the influence of low abundances of O3 and reactive nitrogen (NOy) due to ozone depletion and sedimentation of NOy-containing particles, respectively. On the basis of the different altitude and time ranges of these effects, we conclude that the substantial chlorine deactivation into HCl at 380 K arose as a result of very low ozone abundances together with low temperatures. Additionally, CLaMS estimates ozone depletion of at least 0.4 ppmv at 380 K and 1.75 ppmv at 490 K, which is comparable to other extremely cold Arctic winters. We have used CLaMS trajectories to analyze the history of enhanced ClONO2 measured by GLORIA. In February, most of the enhanced ClONO2 is traced back to chlorine deactivation that had occurred within the past few days prior to the GLORIA measurement. In March, after the final warming, air masses in which chlorine has previously been deactivated into ClONO2 have been transported in the remnants of the polar vortex towards the location of measurement for at least 11 d.

Multi-scale time dependent correlation between synchronous measurements of ground-level ozone and meteorological parameters in the Caribbean Basin

Ground-level ozone (O3) is a major air pollutant which is strongly links to weather conditions. To our knowledge, there are few analysis of O3 behavior in Caribbean region. The aim of this paper is to study the correlation between O3 and meteorological parameters (i.e., solar radiation, temperature, relative humidity and wind speed) in a multi-scale way. Firstly, we estimate their Fourier power spectra and consider their scaling properties in the physical space. The power spectra computed follows a power law behavior for all datasets. Thereafter, the multiple scale dynamics and the correlations between simultaneous measurements of O3 and meteorological parameters was analyzed using the Empirical Mode Decomposition (EMD) based methods. After EMD decomposition of each time series, we investigate their local correlations using a new cross-correlation technique termed Time Dependent Intrinsic Correlation method (TDIC). The time evolution and the scale dependence of their correlation are determined at different time scales and for different intrinsic modes functions. All measured TDICs have highlighted strong correlations between O3 and meteorological parameters. The impact of weather conditions (e.g., drought, rainfall, windy period) have been locally observed on O3 formation for all the time scales. This study shows that TDIC method is a powerful tool for perform multi-scale cross-correlation analysis in air pollution field.

Impacts of holiday characteristics and number of vacation days on “holiday effect” in Taipei: Implications on ozone control strategies

This study investigated the influence of holiday characteristics and numbers of vacation days on the “holiday effect” of three crucial Chinese holidays in Taipei. Surface measurements of NOx, CO, NMHC, O3, SO2, and PM10 from 13 air quality-monitoring stations of the Taiwan Environmental Protection Administration (TEPA) in the Taipei metropolitan area during holiday and non-holiday periods of 1994–2012 were used.All six pollutants were proven to exhibit holiday effects between Chinese New Year (CNY) and non-Chinese New Year (NCNY) periods. However, almost all pollutants exhibited holiday effects for the two other holidays; the exceptions were O3 between Tomb Sweeping Day (TSD) and non-Tomb Sweeping Day (NTSD) periods and CO and PM10 between Mid-Autumn Day (MAD) and non-Mid-Autumn Day (NMAD) periods. Air pollutants, including NOx, CO, NMHC, SO2, and PM10, that exhibited holiday effects had consistently lower concentrations in holiday periods than in non-holiday periods, whereas O3 concentrations were higher in holiday periods than in non-holiday periods. A widespread holiday effect with consistent signs indicates a high degree of urbanization in the study area. Compared with CNY–NCNY and MAD–NMAD periods, the TSD–NTSD period had a considerably lower difference of the titration effect, lower NOx resulting in less ozone destruction, in evening traffic hours and an inconsistent holiday effect in the daytime and nighttime, leading to the lack of O3 holiday effect. Because the MAD period had more nighttime activities than the other two holiday periods did, the MAD–NMAD period lacked CO and PM10 holiday effects. The prevalently higher ratios of CO, NMHC, SO2, and PM10 relative to NOx as a proxy of mobile sources and a lower PM2.5/PM10 ratio in the MAD period than in the CNY and TSD periods indicate different pollution sources oriented from holiday activities.The air pollutants exhibited a weakening trend are all associated with a greater improvement in air quality during the non-holiday periods than the holiday periods, which implies successful air pollution control policies. Holiday effects of NOx, NMHC (p < 0.05), and CO (p < 0.10) are associated with mobile sources; the holiday effects for the three holidays tend to have a strong relation with the number of vacation days in a holiday, indicating that a large reduction of air pollution occurs when a holiday has a high number of vacation days, which probably encourages extensive behavioral changes. Moreover, the aforementioned conditions imply that air pollution control strategies are effective with time; pollution reduction for only 1–2 days may fail to improve ambient air quality. Holiday effects of pollutants emitted during long holiday periods have crucial implications in formulating ozone control strategies in Taiwan and in other countries with similar national or cultural holidays.

Boundary layer ozone in the Northern Colorado Front Range in July–August 2014 during FRAPPE and DISCOVER-AQ from vertical profile measurements

Data from ground-based ozone (O3) vertical profiling platforms operated during the FRAPPE/DISCOVER-AQ campaigns in summer 2014 were used to characterize key processes responsible for establishing O3 profile development in the boundary layer in the Northern Colorado Front Range. Morning mixing from the upper boundary layer and lower free troposphere into the lower boundary layer was the key process establishing the mid-morning boundary layer O3 mixing ratio. Photochemical O3 production throughout the boundary layer builds on the mid-morning profile. From late morning to mid-afternoon the continuing O3 increase was nearly uniform through the depth of the profile measured by the tethersonde (~400 m). Ozonesondes flown on a near daily schedule over a four week period with multiple profiles on a number of days captured the full 1500 to 2000 m vertical extent of O3 enhancements in the mixed boundary layer confirming O3 production throughout the entire boundary layer. Continuous O3 measurements from the Boulder Atmospheric Observatory (BAO) tall tower at 6 m and 300 m showed hourly O3 at the 6 m level ≥75 ppb on 15% of the days. The diurnal variation on these days followed a pattern similar to that seen in the tethersonde profiles. The association of high O3 days at the BAO tower with transport from sectors with intense oil and natural gas production toward the northeast suggests emissions from this industry were an important source of O3 precursors and are crucial in producing peak O3 events in the NCFR. Higher elevation locations to the west of the NCFR plains regularly experience higher O3 values than those in the lower elevation NCFR locations. Exposure of populations in these areas is not captured by the current regulatory network, and likely underestimated in population O3 exposure assessments.