Photochemical Ozone Production Research Articles

Air Quality in the Northern Colorado Front Range Metro Area: The Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ)

AbstractWe describe the resources used, the deployment strategy, and the outcomes of the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) experiment, which took place in the summer of 2014 in the Front Range of Colorado. We provide a history of air quality of the region and the outcomes of previously conducted experiments, describe the atmospheric conditions encountered during the campaign, and summarize the scientific findings that the campaign produced, together with the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER‐AQ) intensive, simultaneously carried out by the National Aeronautics and Space Administration. The goal of FRAPPÉ was to measure emission tracers and photochemical tracers from the ground and by aircraft to be able to quantify the contributions of various emission sectors to the photochemical production of ozone in the Colorado Front Range. We found major contributions from the fossil fuel extraction sector as well as the transportation sector, with minor contributions from agriculture, energy generation, and industry. The meteorological conditions were also found to be critical in creating situations conducive to high ozone in the area.

Simulation of the photochemical ozone production coming from neighbourhood: A case applied in 150 countries

The main objective of this research is to analyse and compare the photochemical ozone production coming from one neighbourhood initially located in Belgium. Which the same neighbourhood design is applied in150 countries, by applying four parameters adapted to each country such as: energy mix, local climate, building materials and occupants’ mobility. In addition, this research evaluates the induced environmental costs of the neighbourhood over a life cycle of 100 years in some regions located on the five continents, and examines the effect of photovoltaic panel on the photochemical ozone concentration. This environmental impact was evaluated by the Pleiades ACV simulation software under four phases (construction, use, renovation, and demolition), before being translated into environmental costs. The results show that in the case of sustainable neighbourhoods, the photochemical ozone production is 14.3% higher in the Low than High income countries. Photovoltaic panel has a significant effect on the photochemical ozone production, indeed, it allows to reduce up to 8.6% of this one. By 2030, if each of the 150 studied countries, increases up to 30% the renewable energy rate in its own energy mix, to the current examples of countries such as: Denmark, Finland, Sweden, Switzerland, Costa Rica, DRC, Nepal, Tajikistan ..., so, Photochemical Ozone Production will decrease from 32% to 45% depending on the region. An average of 56% of photochemical ozone potential (POP) is produced during the operational phase of the neighbourhood.

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.

Photocatalytic conversion of ethane: status and perspective

Ethane (C2H6) is a main component of natural gas and a notable contributor to photochemical pollution and ozone production in the atmosphere. It is important to convert ethane to useful chemicals. The photocatalytic conversion of ethane is promising but challenging. As the first review article in this area, we summarize the recent important progresses in photocatalytic ethane conversion, with an emphasis on (1) homogeneously functionalization and (2) heterogeneously partial oxidation of ethane. Furthermore, the challenges and future directions are provided for the photocatalytic conversion of ethane.

The Life-Cycle Environmental Impact of Recycling of Restaurant Food Waste in Lanzhou, China

The recycling of restaurant food waste can bring environmental benefits and improve food safety for urban residents. We here assessed the entire life cycle of the anaerobic digestion–aerobic composting technique of restaurant food waste recycling using Lanzhou as a case study. We used the CML2001 method provided with the Gabi software and compared the results to those produced using the traditional treatment techniques (landfill and incineration). This work includes a sensitivity analysis of the results. It is here concluded that the anaerobic digestion–aerobic composting technique had the smallest environmental impact of the methods here examined. The life cycle of anaerobic digestion–aerobic composting primarily consumes water, clay, coal, crude oil, and natural gas. The pre-processing phase consumes the most resources, and anaerobic digestion showed the greatest environmental impact. Specific environmental impacts in order from the highest to lowest potential to exacerbate global warming were found to be photochemical ozone production, acidification, eutrophication, marine aquatic ecotoxicity, human toxicity, freshwater aquatic ecotoxicity, and terrestrial ecotoxicity. The main factors associated with different environmental impacts and the environmental impacts themselves were found to differ across different phases. Some environmental impacts were shown to be sensitive to electricity, and the eutrophication potential and photochemical ozone creation potential showed the least sensitivity to all variables. To reduce the environmental impact of the anaerobic digestion–aerobic composting treatment technique, the energy structure and consumption of electricity, water, and diesel need to be optimized.

Photochemical production of ozone and emissions of NO<sub><i>x</i></sub> and CH<sub>4</sub> in the San Joaquin Valley

Abstract. Midday summertime flight data collected in the atmospheric boundary layer (ABL) of California's San Joaquin Valley (SJV) are used to investigate the scalar budgets of NOx, O3, and CH4, in order to quantify the individual processes that control near-surface concentrations, yet are difficult to constrain from surface measurements alone: these include, most importantly, horizontal advection and entrainment mixing from above. The setting is a large mountain–valley system with a small aspect ratio, where topography and persistent temperature inversions impose strong restraints on ABL ventilation. In conjunction with the observed time rates of change this airborne budgeting technique enables us to deduce net photochemical ozone production rates and emission fluxes of NOx and CH4. Estimated NOx emissions from our principal flight domain averaged 216 (±33) t d−1 over six flights in July and August, which is nearly double the California government's NOx inventory for the surrounding three-county region. We consider several possibilities for this discrepancy, including the influence of wildfires, the temporal bias of the airborne sampling, instrumental interferences, and the recent hypothesis presented by Almaraz et al. (2018) of localized high soil NO emissions from intensive agricultural application of nitrogen fertilizers in the region and find the latter to be the most likely explanation. The methane emission average was 438 Gg yr−1 (±143), which also exceeds the emissions inventory for the region by almost a factor of 2. Measured ABL ozone during the six afternoon flights averaged 74 ppb (σ=9.8 ppb). The average midafternoon ozone rise of 2.8 ppb h−1 was found to be comprised of −0.8 ppb h−1 due to horizontal advection of lower O3 levels upwind, −2.5 ppb h−1 from dry deposition loss, −0.5 ppb h−1 from dilution by entrainment mixing, and 6.9 ppb h−1 net in situ photochemical production. The O3 production rates exhibited a dependence on NO2 concentrations (r2=0.35) and no discernible dependence on methane concentrations (r2∼0.02), which are correlated with many of the dominant volatile organic compounds in the region, suggesting that the ozone chemistry was predominantly NOx-limited on the flight days. Additionally, in order to determine the heterogeneity of the different scalars, autocorrelation lengths were calculated for potential temperature (18 km), water vapor (18 km), ozone (30 km), methane (27 km), and NOx (28 km). The spatially diffuse patterns of CH4 and NOx seem to imply a preponderance of broad areal sources rather than localized emissions from cities and/or highway traffic within the SJV.

Fast Photochemistry in Wintertime Haze: Consequences for Pollution Mitigation Strategies.

In contrast to summer smog, the contribution of photochemistry to the formation of winter haze in northern mid-to-high latitude is generally assumed to be minor due to reduced solar UV and water vapor concentrations. Our comprehensive observations of atmospheric radicals and relevant parameters during several haze events in winter 2016 Beijing, however, reveal surprisingly high hydroxyl radical oxidation rates up to 15 ppbv/h, which is comparable to the high values reported in summer photochemical smog and is two to three times larger than those determined in previous observations during winter in Birmingham (Heard et al. Geophys. Res. Lett. 2004, 31, (18)), Tokyo (Kanaya et al. J. Geophys. Res.: Atmos. 2007, 112, (D21)), and New York (Ren et al. Atmos. Environ. 2006, 40, 252-263). The active photochemistry facilitates the production of secondary pollutants. It is mainly initiated by the photolysis of nitrous acid and ozonolysis of olefins and maintained by an extremely efficiently radical cycling process driven by nitric oxide. This boosted radical recycling generates fast photochemical ozone production rates that are again comparable to those during summer photochemical smog. The formation of ozone, however, is currently masked by its efficient chemical removal by nitrogen oxides contributing to the high level of wintertime particles. The future emission regulations, such as the reduction of nitrogen oxide emissions, therefore are facing the challenge of reducing haze and avoiding an increase in ozone pollution at the same time. Efficient control strategies to mitigate winter haze in Beijing may require measures similar as implemented to avoid photochemical smog in summer.

The Eulerian urban dispersion model EPISODE – Part 2: Extensions to the source dispersion and photochemistry for EPISODE–CityChem v1.2 and its application to the city of Hamburg

Abstract. This paper describes the CityChem extension of the Eulerian urban dispersion model EPISODE. The development of the CityChem extension was driven by the need to apply the model in largely populated urban areas with highly complex pollution sources of particulate matter and various gaseous pollutants. The CityChem extension offers a more advanced treatment of the photochemistry in urban areas and entails specific developments within the sub-grid components for a more accurate representation of dispersion in proximity to urban emission sources. Photochemistry on the Eulerian grid is computed using a numerical chemistry solver. Photochemistry in the sub-grid components is solved with a compact reaction scheme, replacing the photo-stationary-state assumption. The simplified street canyon model (SSCM) is used in the line source sub-grid model to calculate pollutant dispersion in street canyons. The WMPP (WORM Meteorological Pre-Processor) is used in the point source sub-grid model to calculate the wind speed at plume height. The EPISODE–CityChem model integrates the CityChem extension in EPISODE, with the capability of simulating the photochemistry and dispersion of multiple reactive pollutants within urban areas. The main focus of the model is the simulation of the complex atmospheric chemistry involved in the photochemical production of ozone in urban areas. The ability of EPISODE–CityChem to reproduce the temporal variation of major regulated pollutants at air quality monitoring stations in Hamburg, Germany, was compared to that of the standard EPISODE model and the TAPM (The Air Pollution Model) air quality model using identical meteorological fields and emissions. EPISODE–CityChem performs better than EPISODE and TAPM for the prediction of hourly NO2 concentrations at the traffic stations, which is attributable to the street canyon model. Observed levels of annual mean ozone at the five urban background stations in Hamburg are captured by the model within ±15 %. A performance analysis with the FAIRMODE DELTA tool for air quality in Hamburg showed that EPISODE–CityChem fulfils the model performance objectives for NO2 (hourly), O3 (daily max. of the 8 h running mean) and PM10 (daily mean) set forth in the Air Quality Directive, qualifying the model for use in policy applications. Envisaged applications of the EPISODE–CityChem model are urban air quality studies, emission control scenarios in relation to traffic restrictions and the source attribution of sector-specific emissions to observed levels of air pollutants at urban monitoring stations.

Enhanced Ozone Production in Ambient Air at Patiala Semi-Urban Site During Crop Residue Burning Events

The continuous in situ measurements of criteria pollutants (O3, CO and NOx) and meteorological variables were done at a semi-urban site (Patiala) of North-West Indo-Gangetic Plains (NW-IGP) for the years 2014 and 2015. The influence of meteorology on the levels of criteria pollutants was investigated on daily, monthly, seasonal and diurnal basis. The average rate of increase in O3, calculated to be 1.1 ppb h−1 and pollution index (daily O3 max/O3 min ratio), values (10.2) indicates remarkable ozone pollution. Ozone is negatively correlated (represented as r value) with its precursor gases CO (− 0.28) and NOx (− 0.32), as they get consumed in the photochemical production of ozone. The impact of meteorology on ozone production was positively correlated with SR (0.63), AT (0.49), MT (0.59) and WS (0.23) and negatively correlated with RH (− 0.83). Pre-, during and post-biomass burning periods were determined using Terra-MODIS images over the study area. Enhanced levels of ozone were recorded as 20 ppb and 15 ppb during daytime, respectively, for rice and wheat crop seasons, and 12 ppb during nighttime for both seasons. Ozone exceedance of 24 h national standard occurred on 50% and 8% of the sampling periods during wheat and rice crop residue burning, respectively. Ozone generation with its precursor gases was analyzed quantitatively.

Effects of aerosols on the surface ozone generation via a study of the interaction of ozone and its precursors during the summer in Shanghai, China

Previous studies have shown that heavy aerosol pollution can inhibit the surface ozone generation. More recent studies, however, have revealed that aerosol loading is positively correlated with ozone concentrations in large cities, such as Shanghai, particularly during the summer. Whether the correlation between aerosol pollution and ozone concentrations is positive or negative, it is an issue that needs to be considered by atmospheric scientists. Although the presence of ozone precursors, such as nitrogen oxide (NOx) and volatile organic compounds (VOCs), affect ozone concentrations, the roles of aerosols in the formation of ozone have rarely been investigated. Therefore, an analysis of the effect of aerosols on photochemical ozone generation via a study of the interaction of ozone and its precursors is important. In our research, we found that both aerosol and ozone concentrations were higher in Shanghai under polluted conditions than they were under clean conditions during the summer, but the ozone formation was controlled by VOCs, not by aerosol loading. The decrease in the AOD (SSA) increased (decreased) the surface UV radiation and promoted (inhibited) photochemical ozone production. We also found that the lower the concentration of photochemically active VOCs, the weaker the effect of the AOD on the ozone concentrations. The other results were shown as follows: (1) Aerosol pollution decreased the amount of UV radiation reaching the Earth's surface, but the surface UV radiation increased with increasing aerosol particle scattering; (2) Aerosol pollution inhibited the photolysis of nitrogen dioxide (NO2), while the scattering property of aerosols facilitated this phenomenon; (3) When both the concentration of ozone precursors and the SSA were constant, the ozone concentration decreased, but the attenuation rate increased significantly with an increase in AOD.

Characterising the seasonal and geographical variability in tropospheric ozone, stratospheric influence and recent changes

Abstract. The stratospheric contribution to tropospheric ozone (O3) has been a subject of much debate in recent decades but is known to have an important influence. Recent improvements in diagnostic and modelling tools provide new evidence that the stratosphere has a much larger influence than previously thought. This study aims to characterise the seasonal and geographical distribution of tropospheric ozone, its variability, and its changes and provide quantification of the stratospheric influence on these measures. To this end, we evaluate hindcast specified-dynamics chemistry–climate model (CCM) simulations from the European Centre for Medium-Range Weather Forecasts – Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model and the Canadian Middle Atmosphere Model (CMAM), as contributed to the International Global Atmospheric Chemistry – Stratosphere-troposphere Processes And their Role in Climate (IGAC-SPARC) (IGAC–SPARC) Chemistry Climate Model Initiative (CCMI) activity, together with satellite observations from the Ozone Monitoring Instrument (OMI) and ozone-sonde profile measurements from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) over a period of concurrent data availability (2005–2010). An overall positive, seasonally dependent bias in 1000–450 hPa (∼0–5.5 km) sub-column ozone is found for EMAC, ranging from 2 to 8 Dobson units (DU), whereas CMAM is found to be in closer agreement with the observations, although with substantial seasonal and regional variation in the sign and magnitude of the bias (∼±4 DU). Although the application of OMI averaging kernels (AKs) improves agreement with model estimates from both EMAC and CMAM as expected, comparisons with ozone-sondes indicate a positive ozone bias in the lower stratosphere in CMAM, together with a negative bias in the troposphere resulting from a likely underestimation of photochemical ozone production. This has ramifications for diagnosing the level of model–measurement agreement. Model variability is found to be more similar in magnitude to that implied from ozone-sondes in comparison with OMI, which has significantly larger variability. Noting the overall consistency of the CCMs, the influence of the model chemistry schemes and internal dynamics is discussed in relation to the inter-model differences found. In particular, it is inferred that CMAM simulates a faster and shallower Brewer–Dobson circulation (BDC) compared to both EMAC and observational estimates, which has implications for the distribution and magnitude of the downward flux of stratospheric ozone over the most recent climatological period (1980–2010). Nonetheless, it is shown that the stratospheric influence on tropospheric ozone is significant and is estimated to exceed 50 % in the wintertime extratropics, even in the lower troposphere. Finally, long-term changes in the CCM ozone tracers are calculated for different seasons. An overall statistically significant increase in tropospheric ozone is found across much of the world but particularly in the Northern Hemisphere and in the middle to upper troposphere, where the increase is on the order of 4–6 ppbv (5 %–10 %) between 1980–1989 and 2001–2010. Our model study implies that attribution from stratosphere–troposphere exchange (STE) to such ozone changes ranges from 25 % to 30 % at the surface to as much as 50 %–80 % in the upper troposphere–lower stratosphere (UTLS) across some regions of the world, including western Eurasia, eastern North America, the South Pacific and the southern Indian Ocean. These findings highlight the importance of a well-resolved stratosphere in simulations of tropospheric ozone and its implications for the radiative forcing, air quality and oxidation capacity of the troposphere.

Temporal Changes in Air Quality during a Festival Season in Kannur, India

This study looked at the variation in air quality during the periods of fireworks as assessed from the change in ambient concentrations of air pollutants like particulate matter (PM10), O3, and NO2 for pre-, post-, and Vishu days for four consecutive years in 2015, 2016, 2017, and 2018 in Kannur, India. Enhanced levels of O3, NO2, NO, and PM10 were observed during the intense usage of fireworks. The concentration of metals in PM10 increased and the percent increase was found to be different for metal traces. A pronounced increase in the aerosol optical depth (AOD) in the lower wavelength region of solar radiation reveals the abundance of fine mode particles. The concentrations of O3 and NO2 were observed to increase by more than 100% on Vishu day than the control days for the observational period. Simulation using the National Center for Atmospheric Research (NCAR) Master Mechanism photochemical box model indicates a more than 100% enhancement in NO2 photolysis rates during the fireworks episode, which leads to a 100% increase in the surface ozone production. Observations as well as model simulations indicate that the enhanced photochemical ozone production from NO2 photolysis is possibly the main driver of ozone production during the Vishu at this site. The air quality index (AQI) revealed the deterioration of air quality at the observational site during the period of Vishu.

Measured and modelled ozone photochemical production in the Baltimore-Washington airshed

Abstract Ozone production efficiency (OPE) represents the number of ozone (O3) molecules produced per molecule of NOx (NO2+NO), before NOx is converted to a sink or reservoir species. Observations from NASA's July 2011 DISCOVER-AQ (D-AQ) campaign in the Baltimore-Washington region are used to quantify OPE, which is compared to output from the Community Multiscale Air Quality (CMAQ) model. The baseline model run of CMAQ (CB05-TUCL mechanism; mobile NOx emissions from the National Emissions Inventory; biogenic emissions from BEIS model v3.61) underestimates observed OPE by 34 ± 20%. The payload of D-AQ lacked direct observations of HO2 and RO2, so we infer the rate at which these peroxy radicals react with NO (termed inROx) from observations of NO, NO2, O3, and j(NO2). The baseline run of CMAQ underestimates inROx by 35 ± 19%. A modified run of CMAQ with a factor of 10 reduction in the lifetime of organic nitrates, a factor of 2 reduction in mobile NOx emissions, an update to the thermal dissociation rate of PAN and PANX to the IUPAC 2014 value, and a correction for the rate constant for OH + PANX results in better overall model performance based on a number of comparisons to data that include column NO2 measured by the Ozone Monitoring Instrument, a value of OPE that is 21 ± 13% less than observed, and inROx that is low by 30 ± 19%. Sensitivity analysis indicates that the peroxy radical discrepancy involves either emission of VOCs other than isoprene or HCHO, or a problem with the model production of HO2 and RO2. Our analysis suggests surface O3 may exhibit stronger declines to further reductions of NOx than is indicated by baseline runs of CMAQ. Index terms Troposphere: constituent transport and chemistry.

Fog geoengineering to abate local ozone pollution at ground level by enhancing air moisture

High concentrations of ozone (O3) at ground level in urban and industrial regions worldwide have long been a major air pollution issue, notably during daytime because sunlights induce the photochemical production of ozone. After a review of actual techniques to clean O3 pollution in urban and industrial regions, I present a fog geoengineering scheme for abating ozone pollution at ground level by enhancing ambient moisture locally through spraying water mist into the atmosphere. This scheme is based on my results showing that ozone levels decrease with air relative humidity. For instance, the mean O3 concentrations decrease from 70.0 to 21.2 ppbv when relative humidity increases from below 40% to more than 80%, in Hangzhou city at midday times (11:00–16:00) without precipitation, during the “ozone season” from May to October of 2017. The mechanism of fog geoengineering is that atmosphere moisture inhibits O3 formation by lowering air temperature, decreasing the chain length of peroxy radical chemical amplifiers (HO2, RO2, and RC(O)O2), and decreasing the chain length of NO2 by enhancing particle water, and destroys the existing O3 photo-chemically by water vapor through catalytic O3 destruction cycle. Ozone mitigation by fog geoengineering has several advantages such as being a nature-like process, quick response, technological feasibility, efficacy, relatively low cost, and cooling effects. The proposed fog geoengineering to decrease the local O3 at ground level could potentially be on avenue for addressing heavy O3 pollution during the hot summer in megacities globally as expected.

Characteristics of Atmospheric Boundary Layer Structure during PM2.5 and Ozone Pollution Events in Wuhan, China

In this study, we investigated six air pollutants from 21 monitoring stations scattered throughout Wuhan city by analyzing meteorological variables in the atmospheric boundary layer (ABL) and air mass backward trajectories from HYSPLIT during the pollution events. Together with this, ground meteorological variables were also used throughout the investigation period: 1 December 2015 to 30 November 2016. Analysis results during this period show that the city was polluted in winter by PM2.5 (particulate matter with aerodynamics of less than 2.5 microns) and in summer by ozone (O3). The most polluted day during the investigation period was 25 December 2015 with an air quality index (AQI) of 330 which indicates ‘severe pollution’, while the cleanest day was 26 August 2016 with an AQI of 27 indicating ‘excellent’ air quality. The average concentration of PM2.5 (O3) on the most polluted day was 265.04 (135.82) µg/m3 and 9.10 (86.40) µg/m3 on the cleanest day. Moreover, the percentage of days which exceeded the daily average limit of NO2, PM10, PM2.5, and O3 for the whole year was 2.46%, 14.48%, 23.50%, and 39.07%, respectively, while SO2 and CO were found to be below the set daily limit. The analysis of ABL during PM2.5 pollution events showed the existence of a strong inversion layer, low relative humidity, and calm wind. These observed conditions are not favorable for horizontal and vertical dispersion of air pollutants and therefore result in pollutant accumulation. Likewise, ozone pollution events were accompanied by extended sunshine hours, high temperature, a calm wind, a strongly suspended inversion layer, and zero recorded rainfall. These general characteristics are favorable for photochemical production of ozone and accumulation of pollutants. Apart from the conditions of ABL, the results from backward trajectories suggest trans-boundary movement of air masses to be one of the important factors which determines the air quality of Wuhan.

Transboundary ozone pollution across East Asia: daily evolution and photochemical production analysed by IASI + GOME2 multispectral satellite observations and models

Abstract. We characterise a transboundary ozone pollution outbreak transported across East Asia in early May 2009 using new multispectral satellite observations of lowermost tropospheric ozone (located below 3 km altitude) in synergy with other satellite data and models. Our analysis is focused on the daily evolution of ozone pollution plumes initially formed over the North China Plain (NCP) and their transport pathways over northern China, Korea, Japan and the surrounding seas. A main aspect of the study is an estimation of the contribution of photochemical production of ozone during transport using the ratio of ozone to carbon monoxide enhancements with respect to background levels derived from satellite data and also from chemistry–transport models.A key contribution of the analysis is the use of new satellite data offering unprecedented skills to observe the horizontal distribution of lowermost tropospheric ozone over East Asia on a daily basis, with a multispectral approach called IASI + GOME2 (combining Infrared Atmospheric Sounding Interferometer observations in the IR and Global Ozone Monitoring Experiment-2 measurements in the UV). These satellite observations are in good agreement with ozonesondes, with low mean biases (3 %), a precision of about 16 %, a correlation coefficient of 0.85 and practically the same standard deviation for a comparison based on 2 years of data from 46 launching stations distributed worldwide, during all seasons. A similar agreement is also found over East Asia. Moreover, IASI + GOME2 offers a unique capacity for observing the evolution of near-surface ozone during pollution outbreaks (with 5 % bias and 0.69 correlation), according to a comparison with surface in situ measurements during two major ozone events over several Japanese islands. Single-band ozone retrievals, such as those from IASI in the thermal infrared, do not capture such variability.Using IASI + GOME2, we show that (i) ozone pollution plumes are transported by an anticyclonic circulation around the Yellow Sea from the NCP to northern China, Korea and Japan, collocated with carbon monoxide plumes; (ii) over northern China the plume splits into two pollution filaments with one mixing with freshly emitted pollutants; and (iii) ozone is produced every day of the event, accounting for an enhancement in concentration during transport across East Asia of up to ∼ 84 % with respect to that produced over NCP. This estimation is done according to monotonically increasing values during 7 days of the ratio of ozone to carbon monoxide enhancements within the transported pollution plumes from about ∼ 0.25 over the NCP to ∼ 0.46 over the Pacific south of Japan.

Low levels of nitryl chloride at ground level: nocturnal nitrogen oxides in the Lower Fraser Valley of British Columbia

Abstract. The nocturnal nitrogen oxides, which include the nitrate radical (NO3), dinitrogen pentoxide (N2O5), and its uptake product on chloride containing aerosol, nitryl chloride (ClNO2), can have profound impacts on the lifetime of NOx (= NO + NO2), radical budgets, and next-day photochemical ozone (O3) production, yet their abundances and chemistry are only sparsely constrained by ambient air measurements. Here, we present a measurement data set collected at a routine monitoring site near the Abbotsford International Airport (YXX) located approximately 30 km from the Pacific Ocean in the Lower Fraser Valley (LFV) on the west coast of British Columbia. Measurements were made from 20 July to 4 August 2012 and included mixing ratios of ClNO2, N2O5, NO, NO2, total odd nitrogen (NOy), O3, photolysis frequencies, and size distribution and composition of non-refractory submicron aerosol (PM1). At night, O3 was rapidly and often completely removed by dry deposition and by titration with NO of anthropogenic origin and unsaturated biogenic hydrocarbons in a shallow nocturnal inversion surface layer. The low nocturnal O3 mixing ratios and presence of strong chemical sinks for NO3 limited the extent of nocturnal nitrogen oxide chemistry at ground level. Consequently, mixing ratios of N2O5 and ClNO2 were low (< 30 and < 100 parts-per-trillion by volume (pptv) and median nocturnal peak values of 7.8 and 7.9 pptv, respectively). Mixing ratios of ClNO2 frequently peaked 1–2 h after sunrise rationalized by more efficient formation of ClNO2 in the nocturnal residual layer aloft than at the surface and the breakup of the nocturnal boundary layer structure in the morning. When quantifiable, production of ClNO2 from N2O5 was efficient and likely occurred predominantly on unquantified supermicron-sized or refractory sea-salt-derived aerosol. After sunrise, production of Cl radicals from photolysis of ClNO2 was negligible compared to production of OH from the reaction of O(1D) + H2O except for a short period after sunrise.

Low modeled ozone production suggests underestimation of precursor emissions (especially NO<sub><i>x</i></sub>) in Europe

Abstract. High surface ozone concentrations, which usually occur when photochemical ozone production takes place, pose a great risk to human health and vegetation. Air quality models are often used by policy makers as tools for the development of ozone mitigation strategies. However, the modeled ozone production is often not or not enough evaluated in many ozone modeling studies. The focus of this work is to evaluate the modeled ozone production in Europe indirectly, with the use of the ozone–temperature correlation for the summer of 2010 and to analyze its sensitivity to precursor emissions and meteorology by using the regional air quality model, the Comprehensive Air Quality Model with Extensions (CAMx). The results show that the model significantly underestimates the observed high afternoon surface ozone mixing ratios (≥ 60 ppb) by 10–20 ppb and overestimates the lower ones (< 40 ppb) by 5–15 ppb, resulting in a misleading good agreement with the observations for average ozone. The model also underestimates the ozone–temperature regression slope by about a factor of 2 for most of the measurement stations. To investigate the impact of emissions, four scenarios were tested: (i) increased volatile organic compound (VOC) emissions by a factor of 1.5 and 2 for the anthropogenic and biogenic VOC emissions, respectively, (ii) increased nitrogen oxide (NOx) emissions by a factor of 2, (iii) a combination of the first two scenarios and (iv) increased traffic-only NOx emissions by a factor of 4. For southern, eastern, and central (except the Benelux area) Europe, doubling NOx emissions seems to be the most efficient scenario to reduce the underestimation of the observed high ozone mixing ratios without significant degradation of the model performance for the lower ozone mixing ratios. The model performance for ozone–temperature correlation is also better when NOx emissions are doubled. In the Benelux area, however, the third scenario (where both NOx and VOC emissions are increased) leads to a better model performance. Although increasing only the traffic NOx emissions by a factor of 4 gave very similar results to the doubling of all NOx emissions, the first scenario is more consistent with the uncertainties reported by other studies than the latter, suggesting that high uncertainties in NOx emissions might originate mainly from the road-transport sector rather than from other sectors. The impact of meteorology was examined with three sensitivity tests: (i) increased surface temperature by 4 ∘C, (ii) reduced wind speed by 50 % and (iii) doubled wind speed. The first two scenarios led to a consistent increase in all surface ozone mixing ratios, thus improving the model performance for the high ozone values but significantly degrading it for the low ozone values, while the third scenario had exactly the opposite effects. Overall, the modeled ozone is predicted to be more sensitive to its precursor emissions (especially traffic NOx) and therefore their uncertainties, which seem to be responsible for the model underestimation of the observed high ozone mixing ratios and ozone production.

The Controlling Factors of Photochemical Ozone Production in Seoul, South Korea

Author(s): Kim, S; Jeong, D; Sanchez, D; Wang, M; Seco, R; Blake, D; Meinardi, S; Barletta, B; Hughes, S; Jung, J; Kim, D; Lee, G; Lee, M; Ahn, J; Lee, SD; Cho, G; Sung, MY; Lee, YH; Park, R | Abstract: We present the ambient ozone and relevant observed trace gas dataset in Seoul, South Korea, during the Megacity Air Pollution Studies (MAPS)-Seoul field campaign from May to June of 2015 (MAPS-Seoul 2015). We observed two distinctive periods, one with higher and the other with lower daytime ozone levels despite mostly clear conditions for both periods. The importance of peroxy radical contributions to excess ozone production is illustrated by the substantial differences in the Leighton constant (Φ) for the two periods. Moreover, higher levels of hydroxyl radical (OH) reactivity (s–1) were observed during the high ozone episode compared to the low ozone episode by as much as ~5 s–1. The contributions of nitrogen oxides (NOx) to OH reactivity become less important than those of volatile organic compounds (VOCs) during the high ozone episode, which suggests the NOx saturated ozone production regime. It was also notable that the biogenic VOC isoprene consistently contributed the most to OH reactivity from among the observed VOCs during the afternoon throughout the whole field campaign. Finally, we ran multiple box model scenarios to evaluate the ozone production rates of three different air mixtures: a high ozone mixture, a low ozone mixture, and a simulation of the regional air quality. The results indicate that the total OH reactivity levels and the relative contributions of VOCs to NOx play critical roles in ozone production rates. The simulated air quality mixture results in lower OH reactivity, causing lower ozone production rates than those calculated for the high ozone mixture, which clearly indicates the need for further improvements in the regional model to accurately simulate ozone precursors in the region. The results of this study suggest that a comprehensive trace gas dataset combined with observations of the OH reactivity enables us to properly diagnose the photochemistry behind ozone pollution, leading to effective ozone abatement policies.

Source apportionment of non-methane hydrocarbons, NOx and H2S data from a central monitoring station in the Eagle Ford shale, Texas

Unconventional oil and gas exploration in the US has become a significant new source of atmospheric hydrocarbons. Field measurements and monitoring have been initiated to determine integral effects from this geographically dispersed source in and downwind of shale areas, driven mostly by concerns related to photochemical ozone production. The Texas Commission on Environmental Quality (TCEQ) deployed its first air quality monitor near the Eagle Ford shale in south Texas in summer 2013, followed by a more centrally located monitor in winter 2014/15. Here, we report on the latter monitor’s 2015 data, showing at times extraordinarily high levels of saturated hydrocarbons, similar to earlier findings in this area. Using hydrocarbon ratios, we establish that the dominant sources at this site appear to be oil and gas exploration. A non-negative matrix factorization (NMF) analysis revealed six consistent source factors, of which two were associated with pre-existing local sources from car traffic and industry, three with regional oil and gas exploration, and one with diesel emissions. The dominant source factors were associated with evaporative and fugitive emissions, and with flaring and (diesel-powered) compressor engine emissions. The former is a major source of saturated hydrocarbons while the latter is a major source of NOx and unsaturated hydrocarbons, confirming earlier findings. Due to the rural nature of the site, road traffic is a minor NOx source in this area, and the NMF results support inventory estimates showing oil and gas exploration to be the dominant regional source of NOx emissions. The NMF based source apportionment results also suggests that benzene levels in this rural area in 2015, while comparable to levels in Houston now, were probably three to five times lower before the shale boom.