Analysis of surface ozone and nitrogen oxides at urban, semi-rural and rural sites in Istanbul, Turkey

Assessment of ground-level ozone pollution in Türkiye according to new WHO limits

Ground-level ozone is a secondary pollutant and is attributable to respiratory diseases and mortality. For this reason, the World Health Organization (WHO) implemented a new long-term (peak season) limit value for ozone. The previous studies related to ozone in Türkiye were spatially limited to certain locations. In this study, annual mean and peak season ozone concentrations, and limit exceedances were investigated for Türkiye for the year 2021. Moreover, ozone peak seasons were determined for the first time for 126 air quality monitoring stations. The annual mean ozone concentration was determined as 44.3 ± 19.3 µg/m3 whereas the peak season average ozone level was 68.4 ± 27.2 µg/m3. April-September period was the most frequently observed ozone peak season. Among all stations, Erzurum Palandöken was by far the most polluted station in terms of annual mean and limit exceedances of ozone. Ankara Siteler stations have the highest rank in peak season mean. 87 and 83 stations exceeded the short-term and long-term recommendations of WHO, respectively. Four hotspot regions were revealed in terms of peak season exceedance: Adana and surrounding provinces, the surroundings of Burdur and Isparta provinces, and the northeastern and northwestern parts of Türkiye. To protect public health, WHO recommendations for 8-h and peak season limits should be immediately implemented in Turkish regulations.

The effect of military conflict zone in the Middle East on atmospheric persistent organic pollutant contamination in its north

This study aimed to investigate long-range atmospheric transport of selected POPs released due to the effects of military conflicts in regions to the south of Turkey's borders. Ten locations were selected to deploy passive air samplers at varying distances to the border on a southeast-west transect of the country, proximity-grouped as close, middle, and far. Sampling campaign included winter and transition months when desert dust transport events occur. Hypothesis of the study was that a decreasing trend would be observed with increasing distance to the border. Group comparisons based on statistical testing showed that PBDE-183, Σ₄₅PCB, and dieldrin in winter; PBDE-28, PBDE-99, PBDE-154, p,p'-DDE, Σ₁₄PBDE, and Σ₂₅OCP in the transition period; and PBDE-28, PBDE-85, PBDE-99, PBDE-154, PBDE-190, PCB-52, Σ₄₅PCB, p,p'-DDE, and Σ₂₅OCP over the whole campaign had a decreasing trend on the transect. An analysis of concentration ratio to the background showed that long-range atmospheric transport impacted the study sites, especially those of close group in comparison to the local sources. Back-trajectory analyses indicated that there was transport from the conflict areas to sites in the close-proximity group, while farther sampling locations mostly received air masses from Europe, Russia, and former Soviet Union countries, followed by North Africa, rather than the military conflict areas. In consequence, decrease in concentrations with distance and its relation to molecular weight through proportions, diagnostic ratios, analysis of concentration ratio to the background, and back-trajectory analyses support the effect of transport from the military-conflict area to its north.

How does COVID-19 lockdown affect air quality: Evidence from Lanzhou, a large city in Northwest China

Coronavirus disease (COVID-19) has disrupted health, economy, and society globally. Thus, many countries, including China, have adopted lockdowns to prevent the epidemic, which has limited human activities while affecting air quality. These affects have received attention from academics, but very few studies have focused on western China, with a lack of comparative studies across lockdown periods. Accordingly, this study examines the effects of lockdowns on air quality and pollution, using the hourly and daily air monitoring data collected from Lanzhou, a large city in Northwest China. The results indicate an overall improvement in air quality during the three lockdowns compared to the average air quality in the recent years, as well as reduced PM_2.5, PM₁₀, SO₂, NO₂, and CO concentrations with different rates and increased O₃ concentration. During lockdowns, Lanzhou's "morning peak" of air pollution was alleviated, while the spatial characteristics remained unchanged. Further, ordered multi-classification logistic regression models to explore the mechanisms by which socioeconomic backgrounds and epidemic circumstances influence air quality revealed that the increment in population density significantly aggravated air pollution, while the presence of new cases in Lanzhou, and medium- and high-risk areas in the given district or county both increase the likelihood of air quality improvement in different degrees. These findings contribute to the understanding of the impact of lockdown on air quality, and propose policy suggestions to control air pollution and achieve green development in the post-epidemic era.

Analysis of Daily and Diurnal O3-NOx Relationships and Assessment of Local/Regional Oxidant (OX = O3 + NO2) Levels and Associated Human Health Risk at a Coastal Suburban Site of Sfax (Tunisia)

The present study investigated the temporal variability of surface ozone and its nitrogen precursors at the proximity of a traffic crossroad (≈ 22,580 vehicles per day) located in a coastal suburban site of Sfax city (Tunisia). It was performed during January-October, 2010. The study results show that the surface ozone is characterized by a slightly modulated regime between day and night. At traffic-peak hours, the decrease of ozone concentration levels is due to the oxidation reaction of NO into NO₂. Complementary statistical approaches (inter-variable correlation matrix, cluster analysis, representation quality of variables and multiple regression analysis) reveal that the excess of O₃ is mainly affected by the wind speed, temperature, solar radiation and NO₂ with contribution rates of 127, 21, 22 and 12%, respectively. The decrease of O₃ is, however, controlled by NO, relative humidity and boundary layer height with contribution rates of 25, 21 and 16%, respectively. The regional daytime and night-time contributions to O₃ are very different. The daytime intercept which is greater than that of night-time indicates there was a large NO_x independent regional contribution. This could be attributed to the biogenic VOCs effect interfering in the photochemical cycle. It, therefore, implies that the study site is VOC-sensitive. The investigation of the air quality index (AQI) for O₃ and NO₂ showed that more than 86% of the total studied period has a good quality level. Only about 14% of total days are characterized by an acceptable air quality level, however, for a very small number of people are unusually sensitive to air pollution.

Changing Air Quality and the Ozone Weekend Effect during the COVID-19 Pandemic in Toronto, Ontario, Canada

Air pollutants, NO, NO2, and O3, were examined from April to June 2020 and compared to a 10-year (2010–2019) climatology of these pollutants for two monitoring sites in Toronto, Ontario, Canada, coinciding with local lockdown measures during the first wave of the COVID-19 pandemic. NO and NO2 values were lower than any of the preceding 10 years at the two Toronto sites for both weekdays and weekends. Ozone concentrations did not have a corresponding decrease and in fact increased for weekdays, similar to other parts of the world. The well-documented ozone weekend effect was considerably muted during the morning rush hour throughout this pandemic period. A Fisher exact test on hourly averaged data revealed statistically significant record hourly minimums for NO and NO2, but this was not found for ozone, consistent with the aggregate ranking results. These findings are likely the result of considerably reduced vehicular traffic during this time and ozone chemistry in a NOx-saturated (VOC limited) environment. This has important implications for ozone abatement strategies.

Variability of ozone and oxides of nitrogen in the tropical city, Bengaluru, India

Bengaluru, also considered India's Silicon Valley, has seen steady growth in population over the years. Bengaluru's rapid development has resulted in dwindling reservoirs, increased traffic congestion, high levels of air pollution, and, to some measure, a rise in summer temperatures. As a result of these changes in urban form over the last decade, anthropogenic heat fluxes for ozone production have increased. However, an observational study on the effects of growing urbanisation on trace gases in Bengaluru for various seasons and periods of the day is missing. Hence, in situ measurements of O₃, NO, NO₂, and NO_X concentrations were carried out at Bengaluru, India, from January 2015 to December 2018. The data were examined for diurnal and interannual variations in trace gas mixing concentrations. The diurnal trend in O₃ exhibits unimodal behaviour. Changes in photochemistry, local meteorology, and the planetary boundary layer's distinctive features cause a rise in the value of concentrations and lead to a peak. In contrast, the diurnal trend in NO, NO₂, and NO_X displayed a bimodal peak due to the combined effect of vehicular emissions and the planetary boundary layer. The link involving the oxidant OX (O₃ + NO₂) and NOx levels were investigated to determine the NOx-independent regional and NOx-dependent local contributions to OX in the atmosphere. Daytime contributions are higher than night-time contributions, according to the present study. The observed anomalies could be the consequence of photochemical processes that produce OX.

Ambient ozone over mid-Brahmaputra Valley, India: effects of local emissions and atmospheric transport on the photostationary state

This study presents the characteristics of ground level atmospheric ozone (O₃) over the rural mid-Brahmaputra Valley region of the northeastern India. Ozone and oxides of nitrogen (NO_x = NO + NO₂) concentration data were obtained from continuous measurement of O₃ and NO_x housed at the MAPAN-AQM station at Tezpur University. The meteorological parameters were obtained from the same station. The diel, monthly, and seasonal variations of O₃ were studied. The O₃-NO_x photostationary state (PS) was carefully examined and it was found that the net O₃ concertation deviated substantially from the PS during the winter season. The deviation could be attributed to local biomass burning, biogenic VOC emission from forest and agriculture, and long-range transport of peroxyacyl nitrate (PAN). The long-range transport has been ascertained by examining the ventilation coefficients (VC), which correlated with the steep growth of net O₃ concentrations in the morning hours. The HYSPLIT air mass back trajectories were used in concentration-weighted trajectory (CWT) analyses of O₃ to assess the long-range regional transport of O₃ precursors, which positively influenced local O₃ concentrations.

Associations between respiratory health and ambient air quality in Canakkale, Turkey: a long-term cohort study

Few epidemiological studies investigating the association between air pollution and health are available in Turkey. The aim of this cohort-type study is to examine the relationships between ambient air quality, respiratory diseases, and decreases in pulmonary function over a year in three different towns in Canakkale: Canakkale Central town (region I), Lapseki town center (region II), and Can town (region III). Region III had four different sub-regions, which were Can town center (region III-A), and the villages located around Can town, namely Durali (region III-B), Kulfal (region III-C), and Yuvalar (region III-D). In the first stage of the study, a detailed questionnaire was completed by the participants (n = 1152) in face-to-face interviews and pulmonary function test (PFT) was performed. In the second stage of the study, PFT measurements were repeated 1 year after the first stage. Particulate matter, SO₂, NO₂, and ozone were gathered from air quality monitoring stations located in the centers of the three regions. The most polluted area was region III, while region I and region II were the least polluted areas. The risk of pulmonary function decline throughout a year was 2.1 times higher in region III, 2.4 times higher both in regions III-B and III-C, and 1.6 times higher for smokers in all regions. In the present study, ambient air quality was worse in region III (industrialized region), which influenced PFT scores and the prognostics for chronic respiratory diseases. The findings of this study should be considered for future investment plans in this region related to human and environmental health needs.

The spatial variation of O3, NO, NO2 and NO x and the relation between them in two Swedish cities

Ozone and nitrogen oxides (NO _x ) are air pollutants with known associations to adverse health effects on humans. Few studies have simultaneously measured ozone and nitrogen oxides with high spatial resolution. The main aim of this paper was to assess the levels and variation of ground-level ozone, NO₂ and NO _x in two Swedish cities. An additional aim was to describe the levels of these pollutants within and between three different types of measurement sites (regional background, urban background and traffic sites) and within and between different measurement periods of the year. Three weekly sampling campaigns of NO _x and ozone were conducted simultaneously at 20 sites in two Swedish regions using Ogawa badges. Ozone was measured at 20 additional sites in each area. The median ozone concentration for all measurements was statistically significantly higher in Malmö (67 μg/m³) compared to Umeå (56 μg/m³), and in both cities, ozone levels were highest in April. Measurement period was a more important factor for describing the variation in ozone concentrations than the type of measurement site. The levels of NO₂ and NO _x were statistically significantly higher in the Malmö area (8.1 and 12 μg/m³) compared to the Umeå area (4.5 and 8.9 μg/m³). The levels were generally highest at the sites categorized as traffic, while the variability between different seasons was sparse.

PAHs and PCBs in an Eastern Mediterranean megacity, Istanbul: Their spatial and temporal distributions, air-soil exchange and toxicological effects

Istanbul, one of the mega cities in the world located between Asia and Europe, has suffered from severe air pollution problems due to rapid population growth, traffic and industry. Atmospheric levels of PAHs and PCBs were investigated in Istanbul at 22 sampling sites during four different sampling periods using PUF disk passive air samplers and spatial and temporal variations of these chemicals were determined. Soil samples were also taken at the air sampling sites. At all sites, the average ambient air Σ₁₅PAH and Σ₄₁PCB concentrations were found as 85.6 ± 68.3 ng m^-3 and 246 ± 122 pg m^-3, respectively. Phenanthrene and anthracene were the predominant PAHs and low molecular weight congeners dominated the PCBs. The PAH concentrations were higher especially at urban sites close to highways. However, the PCBs showed moderately uniform spatial variations. Except four sites, the PAH concentrations were increased with decreasing temperatures during the sampling period, indicating the contributions of combustion sources for residential heating, while PCB concentrations were mostly increased with the temperature, probably due to enhanced volatilization at higher temperatures from their sources. The results of the Factor Analysis represented the impact of traffic, petroleum, coal/biomass and natural gas combustion and medical waste incineration plants on ambient air concentrations. A similar spatial distribution trend was observed in the soil samples. Fugacity ratio results indicated that the source/sink tendency of soil for PAHs and PCBs depends on their volatility and temperature; soil generally acts as a source for lighter PAHs and PCBs particularly in higher temperatures while atmospheric deposition is a main source for higher molecular weight compounds in local soils. Toxicological effect studies also revealed the severity of air and soil pollution especially in terms of PAHs in Istanbul.

Individual exposure estimates may be erroneous when spatiotemporal variability of air pollution and human mobility are ignored

This study aims to empirically demonstrate the necessity to consider both the spatiotemporal variability of air pollution and individual daily movement patterns in exposure and health risk assessment. It compares four different types of exposure estimates generated by using (1) individual movement data and hourly air pollution concentrations; (2) individual movement data and daily average air pollution data; (3) residential location and hourly pollution levels; and (4) residential location and daily average pollution data. These four estimates are significantly different, which supports the argument that ignoring the spatiotemporal variability of environmental risk factors and human mobility may lead to misleading results in exposure assessment. Additionally, three-dimensional (3D) geovisualization presented in the paper shows how person-specific space-time context is generated by the interactions between air pollution and an individual, and how the different individualized contexts place individuals at different levels of health risk.

Surface ozone levels in the forest and vegetation areas of the Biga Peninsula, Turkey

Spatial and temporal variability of surface ozone in the rural, mountainous and suburban sites of Biga Peninsula, at the northwest of Turkey which is about 300km southwest of Istanbul was investigated using passive samplers and continuous analyzers. A total 10 passive samplers and two continuous analyzers were used between 1.1.2013 and 31.12.2014. OX levels in the study region were examined to understand NOx dependent or independent contribution to ozone. The influences of the meteorological parameters on ozone levels were also examined by wind speed and ambient temperature. The results clearly show that mountainous areas have higher cumulative exposure to ozone than suburban locations. In order to understand the long range transport sources contributing to the high ozone levels in the region backward trajectories were computed using HYSPLIT model and then clustering of trajectories are performed. The results clearly show the characteristics of pollutant transport from north to Biga Peninsula. Additionally, AOT40 (Accumulated hourly O3 concentrations Over a Threshold of 40ppb) cumulative index was calculated using daytime hourly measurements. The results indicate that the ozone values in the study area are much higher than the critical levels for forest and vegetation based on EU Directive 2008/50/EC.

Wavelets-based clustering of air quality monitoring sites

This paper aims at providing a variance/covariance profile of a set of 36 monitoring stations measuring ozone (O3) and nitrogen dioxide (NO2) hourly concentrations, collected over the period 2005-2013, in Portugal mainland. The resulting individual profiles are embedded in a wavelet decomposition-based clustering algorithm in order to identify groups of stations exhibiting similar profiles. The results of the cluster analysis identify three groups of stations, namely urban, suburban/urban/rural, and a third group containing all but one rural stations. The results clearly indicate a geographical pattern among urban stations, distinguishing those located in Lisbon area from those located in Oporto/North. Furthermore, for urban stations, intra-diurnal and daily time scales exhibit the highest variance. This is due to the more relevant chemical activity occurring in high NO2 emissions areas which are responsible for high variability on daily profiles. These chemical processes also explain the reason for NO2 and O3 being highly negatively cross-correlated in suburban and urban sites as compared with rural stations. Finally, the clustering analysis also identifies sites which need revision concerning classification according to environment/influence type.

Exploring the interaction between O₃ and NOx pollution patterns in the atmosphere of Barcelona, Spain using the MCR-ALS method

This work focuses on understanding the behaviour and patterns of three atmospheric pollutants namely, nitric oxide (NO), nitrogen dioxide (NO2), and ozone (O3) along with their mutual interactions in the atmosphere of Barcelona, North Spain. Hourly samples were collected for NO, NO2 and O3 from the same city location for three consecutive years (2010-2012). The study explores the seasonal, annual and weekday-weekend variations in their diurnal profiles along with the possible identification of their source and mutual interactions in the region. Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) was applied to the individual datasets of these pollutants, as well as to all of them simultaneously (augmented mode) to resolve the profiles related to their source and variation patterns in the atmosphere. The analysis of the individual datasets confirmed the source pattern variations in the concerned pollutant's profiles; and the resolved profiles for augmented datasets suggested for the mutual interaction of the pollutants along with their patterns variations, simultaneously. The study suggests vehicular pollution as the major source of atmospheric nitrogen oxides and presence of weekend ozone effect in the region.

Impact of medium-distance pollution sources in a Galician suburban site (NW Iberian peninsula)

This work studies airborne quality in a geographical area that has not been investigated broadly: a suburban site nearby A Coruña (Galicia, NW Iberian Peninsula). In contrast to major Spanish cities, the site has Atlantic characteristics: rainy, scarce calm weather and infrequent prolonged sunny periods. The relationships between several gaseous pollutants (NO, NO2, NOx, CO, O3, PM10, PM2.5 and PM1) and their temporal trends (daily, monthly and seasonal) were evaluated. The aim was to unravel whether medium- and long-distance sources were impacting upon the site. Univariate studies focused on factorizing the pollutants according to a codifying factor (wind direction, hour of the day, season and month). Multivariate studies (Varimax-rotated factorial analysis) were done separately on both weekdays and weekends. The intensity of the daily maxima for NO, NO2, NOx and CO was lower during the weekends, with O3 behaving opposite. PM average values agreed with previous historical reports for a rural background station relatively close to the site and they decreased daily between 11:00 and 19:00 h, likely because of the marine breeze. With moderate wind speeds the pollutants were associated to medium-distance pollution sources, mainly the city of A Coruña and a combination of industrial pollution sources (a power plant, a solid waste incinerator and a regional airport).

Influence of local meteorology and NO2 conditions on ground-level ozone concentrations in the eastern part of Texas, USA

The influence of local climatic factors on ground-level ozone concentrations is an area of increasing interest to air quality management in regards to future climate change. This study presents an analysis on the role of temperature, wind speed, wind direction, and NO₂ level on ground-level ozone concentrations over the region of Eastern Texas, USA. Ozone concentrations at the ground level depend on the formation and dispersion processes. Formation process mainly depends on the precursor sources, whereas, the dispersion of ozone depends on meteorological factors. Study results showed that the spatial mean of ground-level ozone concentrations was highly dependent on the spatial mean of NO₂ concentrations. However, spatial distributions of NO₂ and ozone concentrations were not uniformed throughout the study period due to uneven wind speeds and wind directions. Wind speed and wind direction also played a significant role in the dispersion of ozone. Temperature profile in the area rarely had any effects on the ozone concentrations due to low spatial variations.

Spatial and temporal variation of surface ozone, NO and NO₂ at urban, suburban, rural and industrial sites in the southwest of the Iberian Peninsula

Surface ozone is one of the most important photochemical pollutants in the low atmosphere, causing damage to human health, vegetation, materials and climate. The weather (high temperatures and high solar radiation), orography (presence of the Guadalquivir valley) and anthropogenic (the cities of Cádiz, Córdoba, Huelva and Seville and two important industrial complexes) characteristics of the southwestern Iberian Peninsula make this region ideal for the formation and accumulation of ozone. To increase the knowledge of ozone behaviour in this area, the monthly, daily and weekly variations of ozone and its precursors, nitrogen oxides (NO(x) = NO + NO2), were analysed over a 4-year period (2003 to 2006). Using the k-means cluster technique, 12 representative stations of five different areas with different ozone behaviour were selected from a total of 29 monitoring sites. This is the first time that the analysis of these atmospheric pollutants has been carried out for the whole area, allowing therefore a complete understanding of the dynamics and the relationships of these compounds in this region. The results showed an opposite behaviour among ozone and NO and NO2 concentrations in urban and suburban zones, marked by maximums of ozone (minimums NO(x)) in spring and summer and minimums (maximums) in autumn and winter. A seasonal behaviour, with lower amplitude, was also observed in rural and industrial areas for ozone concentrations, with the NO and NO2 concentrations remaining at low and similar values during the year in rural zones due to the absence of emission sources in their surroundings. The daily cycles of ozone in urban, suburban and industrial sites registered a maximum value in the early afternoon (14:00-17:00 UTC) while for NOx two peaks were observed, at 7:00-10:00 UTC and 20:00-22:00. In the case of rural stations, no hourly peak of ozone or NO(x) was registered. The weekend effect was studied by using a statistical contrast tests (Student's t). The results indicated that only areas influenced by important traffic emissions presented a weekend effect for NO and NO2, whereas an ozone weekend effect was not detected in any case.

Can artificial neural networks be used to predict the origin of ozone episodes?

Tropospheric ozone is a secondary pollutant having a negative impact on health and environment. To control and minimize such impact the European Community established regulations to promote a clean air all over Europe. However, when an episode is related with natural mechanisms as Stratosphere-Troposphere Exchanges (STE), the benefits of an action plan to minimize precursor emissions are inefficient. Therefore, this work aims to develop a tool to identify the sources of ozone episodes in order to minimize misclassification and thus avoid the implementation of inappropriate air quality plans. For this purpose, an artificial neural network model - the Multilayer Perceptron - is used as a binary classifier of the source of an ozone episode. Long data series, between 2001 and 2010, considering the ozone precursors, (7)Be activity and meteorological conditions were used. With this model, 2-7% of a mean error was achieved, which is considered as a good generalization. Accuracy measures for imbalanced data are also discussed. The MCC values show a good performance of the model (0.65-0.92). Precision and F1-measure indicate that the model specifies a little better the rare class. Thus, the results demonstrate that such a tool can be used to help authorities in the management of ozone, namely when its thresholds are exceeded due natural causes, as the above mentioned STE. Therefore, the resources used to implement an action plan to minimize ozone precursors could be better managed avoiding the implementation of inappropriate measures.

Simulated air quality and pollutant budgets over Europe in 2008

Major gaseous and particulate pollutant levels over Europe in 2008 have been simulated using the offline-coupled WRFCMAQ chemistry and transport modeling system. The simulations are compared with surface observations from the EMEP stations, ozone (O3) soundings, ship-borne O3 and nitrogen dioxide (NO2) observations in the western Mediterranean, tropospheric NO2 vertical column densities from the SCIAMACHY instrument, and aerosol optical depths (AOD) from the AERONET. The results show that on average, surface O3 levels are underestimated by 4 to 7% over the northern European EMEP stations while they are overestimated by 7-10% over the southern European EMEP stations and underestimated in the tropospheric column (by 10-20%). Particulate matter (PM) mass concentrations are underestimated by up to 60%, particularly in southern and eastern Europe, suggesting underestimated PM sources. Larger differences are calculated for individual aerosol components, particularly for organic and elemental carbon than for the total PM mass, indicating uncertainty in the combustion sources. Better agreement has been obtained for aerosol species over urban areas of the eastern Mediterranean, particularly for nss-SO4(2), attributed to the implementation of higher quality emission inventories for that area. Simulated AOD levels are lower than the AERONET observations by 10% on average, with average underestimations of 3% north of 40°N, attributed to the low anthropogenic emissions in the model and 22% south of 40°N, suggesting underestimated natural and resuspended dust emissions. Overall, the results reveal differences in the model performance between northern and southern Europe, suggesting significant differences in the representation of both anthropogenic and natural emissions in these regions. Budget analyses indicate that O3 and peroxyacetyl nitrate (PAN) are transported from the free troposphere (FT) to the planetary boundary layer over Europe, while other species follow the reverse path and are then advected away from the source region.