Impact of sea breeze air masses laden with ozone on inland surface ozone concentrations: A case study of the northern coast of Taiwan

Abstract. Ozone, along with other air pollutants, has been measured for two years from a monitoring station placed on a cruise ship that follows a regular track in the Western Mediterranean between April and October. Conditions favoring high ozone levels have been studied by analysis of weather maps and back trajectories. This analysis was focused on a transect over the open sea in the South Western Mediterranean between Tunis and Palma de Mallorca. High ozone levels were found in situations with an anticyclonic circulation over the Western Mediterranean when subsidence brings air masses down from altitudes between 1000 and 3500 m a.s.l. Analysis of composite meteorological maps suggest a relevant contribution of breeze circulation to subsidence during events with high surface ozone concentrations; this points to an important contribution from local ozone formation. A detailed back trajectory analysis of the origin of air masses with high ozone concentrations was carried out for two "hot spots" for ozone pollution, found along the coast south of Genova and between Napoli and Palermo, respectively. While it was found that the influence of plumes from areas with high pollutant levels might explain most episodes in the Northwestern transect, such "local" influences appeared to be of minor importance within the Napoli-Palermo transect.

Download Full-text

Ozone reservoir layers in a coastal environment – a case study in Southern Taiwan

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-1719-2010 ◽

2010 ◽

Vol 10 (1) ◽

pp. 1719-1754

Author(s):

C.-H. Lin ◽

Y.-L. Wu ◽

C.-H. Lai

Keyword(s):

Ozone Concentration ◽

Surface Ozone ◽

Mixing Layer ◽

Ozone Pollution ◽

Ozone Concentrations ◽

Elevated Ozone ◽

Mountain Site ◽

Southern Taiwan ◽

Ozone Episode

Abstract. The air layer between the nocturnal boundary layer and the top of the daily mixing layer in an ozone-polluted area is known to serve as an ozone reservoir since the ozone that is produced in the previous daytime mixing layer can be well preserved throughout the night in the air layer. Ozone reservoir layers are capable of enhancing surface ozone accumulation on the following day. However, our knowledge of the characteristics of ozone reservoir layers and their effects on the daily ozone accumulations is limited. In this work, ozone reservoir layers were experimentally investigated at a coastal, near-mountain site in Southern Taiwan, 30 km away from the coastlines. Tethered ozone soundings were performed to obtain vertical profiles of ozone and meteorological variables during a four-day ozone episode in November 2006. Observation-based methods are adopted to evaluate the influences of the ozone reservoir layers on the surface ozone accumulation during the four-day ozone episode. Ozone reservoir layers were found to develop every evening with a depth of 1200–1400 m. Ozone concentrations within the reservoir layers reached over 140 parts per billion (ppb). From each evening to midnight, the size of the ozone reservoir layer and the ozone concentration inside dramatically changed. As a result, a concentrated, elevated ozone reservoir layer formed with a depth of 400 m at 800–1200 m every midnight. For the rest of each night, the elevated ozone reservoir layer gradually descended until it reached 500–900 m in the next morning. Local circulations and nocturnal subsidence are responsible for the observed evolution. The ozone concentration at the study site was maximal at 15:00–17:00 LT daily because of the addition of the daily produced ozone on the preceding day. Hourly downward mixing ozone concentrations due to the ozone reservoir layers can be as high as 35–45 ppb/h in the late morning. The contribution of the ozone carried over from the preceding day can be 75–85 ppb, which contributes over 50% to the daily ozone pollution as compared with ozone produced on the study day.

Download Full-text

Aerosol-ozone correlations during dust transport episodes

Atmospheric Chemistry and Physics ◽

10.5194/acp-4-1201-2004 ◽

2004 ◽

Vol 4 (5) ◽

pp. 1201-1215 ◽

Cited By ~ 88

Author(s):

P. Bonasoni ◽

P. Cristofanelli ◽

F. Calzolari ◽

U. Bonafè ◽

F. Evangelisti ◽

...

Keyword(s):

Surface Ozone ◽

Coarse Particles ◽

North African ◽

Air Masses ◽

Source Areas ◽

Background Values ◽

Ozone Concentrations ◽

The North ◽

Dust Events ◽

The Impact

Abstract. Its location in the Mediterranean region and its physical characteristics render Mt. Cimone (44°11′ N, 10°42′ E), the highest peak of the Italian northern Apennines (2165 m asl), particularly suitable to study the transport of air masses from the north African desert area to Europe. During these northward transports 12 dust events were registered in measurements of the aerosol concentration at the station during the period June–December 2000, allowing the study of the impact of mineral dust transports on free tropospheric ozone concentrations, which were also measured at Mt. Cimone. Three-dimensional backward trajectories were used to determine the air mass origin, while TOMS Aerosol Index data for the Mt. Cimone area were used to confirm the presence of absorbing aerosol over the measurement site. A trajectory statistical analysis allowed identifying the main source areas of ozone and aerosols. The analysis of these back trajectories showed that central Europe and north and central Italy are the major pollution source areas for ozone and fine aerosol, whereas the north African desert regions were the most important source areas for coarse aerosol and low ozone concentrations. During dust events, the Mt. Cimone mean volume concentration for coarse particles was 6.18 µm3/cm3 compared to 0.63 µm3/cm3 in dust-free conditions, while the ozone concentrations were 4% to 21% lower than the monthly mean background values. Our observations show that surface ozone concentrations were lower than the background values in air masses coming from north Africa, and when these air masses were also rich in coarse particles, the lowest ozone values were registered. Moreover, preliminary results on the possible impact of the dust events on PM10 and ozone values measured in Italian urban and rural areas showed that during the greater number of the considered dust events, significant PM10 increases and ozone decreases have occurred in the Po valley.

Download Full-text

Ozone over the Western Mediterranean Sea – results from two years of shipborne measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-675-2011 ◽

2011 ◽

Vol 11 (2) ◽

pp. 675-688 ◽

Cited By ~ 37

Author(s):

K. Velchev ◽

F. Cavalli ◽

J. Hjorth ◽

E. Marmer ◽

E. Vignati ◽

...

Keyword(s):

Surface Ozone ◽

High Surface ◽

Western Mediterranean ◽

Back Trajectory ◽

Cruise Ship ◽

Ozone Pollution ◽

Back Trajectories ◽

Air Masses ◽

Ozone Concentrations ◽

Ozone Levels

Abstract. Ozone, along with other air pollutants, has been measured for two years from a monitoring station placed on a cruise ship that follows a regular track in the Western Mediterranean between April and October. Conditions favouring high ozone levels have been studied by analysis of weather maps and back trajectories. This analysis was focused on a transect over the open sea in the South Western Mediterranean between Tunis and Palma de Mallorca. High ozone levels were found in situations with an anticyclonic circulation over the Western Mediterranean when subsidence brings air masses down from altitudes between 1000 and 3500 m a.s.l. Analysis of composite meteorological maps suggests a relevant contribution of breeze circulation to subsidence during events with high surface ozone concentrations; this points to an important contribution from local ozone formation. A detailed back trajectory analysis of the origin of air masses with high ozone concentrations was carried out for two "hot spots" for ozone pollution, in the Gulf of Genoa and between Naples and Palermo, respectively. The main cause of high ozone levels in the Gulf of Genoa was found to be outflow from the Po Valley and the Genoa area while such episodes along the Naples-Palermo transect were most often associated with trajectories from the Rome or Naples areas. Analysis of the relationship between measured concentrations of Black Carbon and ozone allowed to evaluate the degree of photochemical "ageing" of the air masses encountered along the route of the cruise ship.

Download Full-text

Aerosol-ozone correlations during dust transport episodes

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-4-2055-2004 ◽

2004 ◽

Vol 4 (2) ◽

pp. 2055-2088 ◽

Cited By ~ 7

Author(s):

P. Bonasoni ◽

P. Cristofanelli ◽

F. Calzolari ◽

U. Bonafè ◽

F. Evangelisti ◽

...

Keyword(s):

Surface Ozone ◽

Coarse Particles ◽

North African ◽

Air Masses ◽

Source Areas ◽

Background Values ◽

Ozone Concentrations ◽

The North ◽

Dust Events ◽

The Impact

Abstract. Its location in the Mediterranean region and its physical characteristics render Mt. Cimone (44°11' N, 10°42' E), the highest peak of the Italian northern Apennines (2165 m asl), particularly suitable to study the transport of air masses from the North African desert area to Europe. During these northward transports 12 dust events were registered in measurements of the aerosol concentration at the station during the period June–December 2000, allowing the study of the impact of mineral dust transports on free tropospheric ozone concentrations, which were also measured at Mt. Cimone. Three-dimensional backward trajectories were used to determine the air mass origin, while TOMS Aerosol Index data for the Mt. Cimone area were used to confirm the presence of absorbing aerosol over the measurement site. A trajectory statistical analysis allowed identifying the main source areas of ozone and aerosols. The analysis of these back trajectories showed that central Europe and North and central Italy are the major pollution source areas for ozone and fine aerosol, whereas the North African desert regions were the most important source areas for coarse aerosol and low ozone concentrations. During dust events, the Mt. Cimone mean volume concentration for coarse particles was 6.18 μm3/cm3 compared to 0.63 μm3/cm3 in dust-free conditions, while the ozone concentrations were 5% to 20% lower than the monthly mean background values. Our observations show that surface ozone concentrations were lower than the background values in air masses coming from North Africa, and when these air masses were also rich in coarse particles, the lowest ozone values were registered. Preliminary results on the impact of the dust events on PM10 values measured in the urban and rural areas of the Po valley are also presented.

Download Full-text

Mangrove Forest Landcover Changes in Coastal Vietnam: A Case Study from 1973 to 2020 in Thanh Hoa and Nghe An Provinces

Forests ◽

10.3390/f12050637 ◽

2021 ◽

Vol 12 (5) ◽

pp. 637

Author(s):

Huong Thi Thuy Nguyen ◽

Giles E. S. Hardy ◽

Tuat Van Le ◽

Huy Quoc Nguyen ◽

Hoang Huy Nguyen ◽

...

Keyword(s):

Mangrove Forest ◽

Monsoon Season ◽

Coastal Development ◽

Northern Coast ◽

Mangrove Forests ◽

Visual Interpretation ◽

Mangrove Restoration ◽

Coast Of Vietnam ◽

Landsat Satellite

Mangrove forests can ameliorate the impacts of typhoons and storms, but their extent is threatened by coastal development. The northern coast of Vietnam is especially vulnerable as typhoons frequently hit it during the monsoon season. However, temporal change information in mangrove cover distribution in this region is incomplete. Therefore, this study was undertaken to detect change in the spatial distribution of mangroves in Thanh Hoa and Nghe An provinces and identify reasons for the cover change. Landsat satellite images from 1973 to 2020 were analyzed using the NDVI method combined with visual interpretation to detect mangrove area change. Six LULC classes were categorized: mangrove forest, other forests, aquaculture, other land use, mudflat, and water. The mangrove cover in Nghe An province was estimated to be 66.5 ha in 1973 and increased to 323.0 ha in 2020. Mangrove cover in Thanh Hoa province was 366.1 ha in 1973, decreased to 61.7 ha in 1995, and rose to 791.1 ha in 2020. Aquaculture was the main reason for the loss of mangroves in both provinces. Overall, the percentage of mangrove loss from aquaculture was 42.5% for Nghe An province and 60.1% for Thanh Hoa province. Mangrove restoration efforts have contributed significantly to mangrove cover, with more than 1300 ha being planted by 2020. This study reveals that improving mangrove restoration success remains a challenge for these provinces, and further refinement of engineering techniques is needed to improve restoration outcomes.

Download Full-text

Behavior of Offshore Pile in Calcareous Sand—Case Study

Journal of Marine Science and Engineering ◽

10.3390/jmse9080839 ◽

2021 ◽

Vol 9 (8) ◽

pp. 839

Author(s):

Tarek N. Salem ◽

Nadia M. Elkhawas ◽

Ahmed M. Elnady

Keyword(s):

Load Capacity ◽

High Stress ◽

Embedment Depth ◽

Shear Stresses ◽

Northern Coast ◽

Compression Tests ◽

Calcareous Sand ◽

Element Analysis ◽

Mixing Ratios

The erosion of limestone and calcarenite ridges that existed parallel to the Mediterranean shoreline forms the calcareous sand (CS) formation at the surface layer of Egypt's northern coast. The CS is often combined with broken shells which are considered geotechnically problematic due to their possible crushability and relatively high compressibility. In this research, CS samples collected from a site along the northern coast of Egypt are studied to better understand its behavior under normal and shear stresses. Reconstituted CS specimens with different ratios of broken shells (BS) are also investigated to study the effect of BS ratios on the soil mixture strength behavior. The strength is evaluated using laboratory direct-shear and one-dimensional compression tests (oedometer test). The CS specimens are not exposed to significant crushability even under relatively high-stress levels. In addition, a 3D finite element analysis (FEA) is presented in this paper to study the degradation offshore pile capacity in CS having different percentages of BS. The stress–strain results using oedometer tests are compared with a numerical model, and it gave identical matching for most cases. The effects of pile diameter and embedment depth parameters are then studied for the case study on the northern coast. Three different mixing ratios of CS and BS have been used, CS + 10% BS, CS + 30% BS, and CS + 50% BS, which resulted in a decrease of the ultimate vertical compression pile load capacity by 8.8%, 15%, and 16%, respectively.

Download Full-text

Temporal patterns and trends of surface ozone concentrations over Portugal

10.5194/egusphere-egu21-5119 ◽

2021 ◽

Author(s):

Carla Gama ◽

Alexandra Monteiro ◽

Myriam Lopes ◽

Ana Isabel Miranda

Keyword(s):

Air Quality ◽

Iberian Peninsula ◽

Human Health ◽

Temporal Variability ◽

Urban Areas ◽

Surface Ozone ◽

Quality Data ◽

Ozone Concentrations ◽

Long Term Study

Tropospheric ozone (O3) is a critical pollutant over the Mediterranean countries, including Portugal, due to systematic exceedances to the thresholds for the protection of human health. Due to the location of Portugal, on the Atlantic coast at the south-west point of Europe, the observed O3 concentrations are very much influenced not only by local and regional production but also by northern mid-latitudes background concentrations. Ozone trends in the Iberian Peninsula were previously analysed by Monteiro et al. (2012), based on 10-years of O3 observations. Nevertheless, only two of the eleven background monitoring stations analysed in that study are located in Portugal and these two stations are located in Porto and Lisbon urban areas. Although during pollution events O3 levels in urban areas may be high enough to affect human health, the highest concentrations are found in rural locations downwind from the urban and industrialized areas, rather than in cities. This happens because close to the sources (e.g., in urban areas) freshly emitted NO locally scavenges O3. A long-term study of the spatial and temporal variability and trends of the ozone concentrations over Portugal is missing, aiming to answer the following questions:-&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; What is the temporal variability of ozone concentrations?-&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; Which trends can we find in observations?-&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; How were the ozone spring maxima concentrations affected by the COVID-19 lockdown during spring 2020?In this presentation, these questions will be answered based on the statistical analysis of O3 concentrations recorded within the national air quality monitoring network between 2005 and 2020 (16 years). The variability of the surface ozone concentrations over Portugal, on the timescales from diurnal to annual, will be presented and discussed, taking into account the physical and chemical processes that control that variability. Using the TheilSen function from the OpenAir package for R (Carslaw and Ropkins 2012), which quantifies monotonic trends and calculates the associated p-value through bootstrap simulations, O3 concentration long-term trends will be estimated for the different regions and environments (e.g., rural, urban).&#160; Moreover, taking advantage of the unique situation provided by the COVID-19 lockdown during spring 2020, when the government imposed mandatory confinement and citizens movement restriction, leading to a reduction in traffic-related atmospheric emissions, the role of these emissions on ozone levels during the spring period will be studied and presented.&#160;Carslaw and Ropkins, 2012. Openair&#8212;an R package for air quality data analysis. Environ. Model. Softw. 27-28,52-61. https://doi.org/10.1016/j.envsoft.2011.09.008Monteiro et al., 2012. Trends in ozone concentrations in the Iberian Peninsula by quantile regression and clustering. Atmos. Environ. 56, 184-193. https://doi.org/10.1016/j.atmosenv.2012.03.069

Download Full-text

Increasing surface ozone concentrations in the background atmosphere of Southern China, 1994–2007

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-6217-2009 ◽

2009 ◽

Vol 9 (16) ◽

pp. 6217-6227 ◽

Cited By ~ 277

Author(s):

T. Wang ◽

X. L. Wei ◽

A. J. Ding ◽

C. N. Poon ◽

K. S. Lam ◽

...

Keyword(s):

Hong Kong ◽

South China ◽

Surface Ozone ◽

Eastern China ◽

Rate Of Change ◽

Urban Site ◽

Coastal Regions ◽

Air Masses ◽

Background Ozone ◽

Rate Of Increase

Abstract. Tropospheric ozone is of great importance with regard to air quality, atmospheric chemistry, and climate change. In this paper we report the first continuous record of surface ozone in the background atmosphere of South China. The data were obtained from 1994 to 2007 at a coastal site in Hong Kong, which is strongly influenced by the outflow of Asian continental air during the winter and the inflow of maritime air from the subtropics in the summer. Three methods are used to derive the rate of change in ozone. A linear fit to the 14-year record shows that the ozone concentration increased by 0.58 ppbv/yr, whereas comparing means in years 1994–2000 and 2001–2007 gives an increase of 0.87 ppbv/yr for a 7-year period. The ozone changes in air masses from various source regions are also examined. Using local wind and carbon monoxide (CO) data to filter out local influence, we find that ozone increased by 0.94 ppbv/yr from 1994–2000 to 2001–2007 in air masses from Eastern China, with similar changes in the other two continent-influenced air-mass groups, but no statistically significant change in the marine air. An examination of the nitrogen dioxide (NO2) column obtained from GOME and SCIAMACHY reveals an increase in atmospheric NO2 in China's three fastest developing coastal regions, whereas NO2 in other parts of Asia decreased during the same period, and no obvious trend over the main shipping routes in the South China Sea was indicated. Thus the observed increase in background ozone in Hong Kong is most likely due to the increased emissions of NO2 (and possibly volatile organic compounds (VOCs) as well) in the upwind coastal regions of mainland China. The CO data at Hok Tsui showed less definitive changes compared to the satellite NO2 column. The increase in background ozone likely made a strong contribution (81%) to the rate of increase in "total ozone" at an urban site in Hong Kong, suggesting the need to consider distant sources when developing long-term strategies to mitigate local ozone pollution.

Download Full-text

Synergetic monitoring of Saharan dust plumes and potential impact on surface: a case study of dust transport from Canary Islands to Iberian Peninsula

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-3067-2011 ◽

2011 ◽

Vol 11 (7) ◽

pp. 3067-3091 ◽

Cited By ~ 63

Author(s):

C. Córdoba-Jabonero ◽

M. Sorribas ◽

J. L. Guerrero-Rascado ◽

J. A. Adame ◽

Y. Hernández ◽

...

Keyword(s):

Iberian Peninsula ◽

Particle Deposition ◽

Ground Level ◽

In Situ Measurements ◽

Saharan Dust ◽

Dust Transport ◽

Air Masses ◽

Potential Impact

Abstract. The synergetic use of meteorological information, remote sensing both ground-based active (lidar) and passive (sun-photometry) techniques together with backtrajectory analysis and in-situ measurements is devoted to the characterization of dust intrusions. A case study of air masses advected from the Saharan region to the Canary Islands and the Iberian Peninsula, located relatively close and far away from the dust sources, respectively, was considered for this purpose. The observations were performed over three Spanish geographically strategic stations within the dust-influenced area along a common dust plume pathway monitored from 11 to 19 of March 2008. A 4-day long dust event (13–16 March) over the Santa Cruz de Tenerife Observatory (SCO), and a linked short 1-day dust episode (14 March) in the Southern Iberian Peninsula over the Atmospheric Sounding Station "El Arenosillo" (ARN) and the Granada station (GRA) were detected. Meteorological conditions favoured the dust plume transport over the area under study. Backtrajectory analysis clearly revealed the Saharan region as the source of the dust intrusion. Under the Saharan air masses influence, AERONET Aerosol Optical Depth at 500 nm (AOD500) ranged from 0.3 to 0.6 and Ångström Exponent at 440/675 nm wavelength pair (AE440/675) was lower than 0.5, indicating a high loading and predominance of coarse particles during those dusty events. Lidar observations characterized their vertical layering structure, identifying different aerosol contributions depending on altitude. In particular, the 3-km height dust layer transported from the Saharan region and observed over SCO site was later on detected at ARN and GRA stations. No significant differences were found in the lidar (extinction-to-backscatter) ratio (LR) estimation for that dust plume over all stations when a suitable aerosol scenario for lidar data retrieval is selected. Lidar-retrieved LR values of 60–70 sr were obtained during the main dust episodes. These similar LR values found in all the stations suggest that dust properties were kept nearly unchanged in the course of its medium-range transport. In addition, the potential impact on surface of that Saharan dust intrusion over the Iberian Peninsula was evaluated by means of ground-level in-situ measurements for particle deposition assessment together with backtrajectory analysis. However, no connection between those dust plumes and the particle sedimentation registered at ground level is found. Differences on particle deposition processes observed in both Southern Iberian Peninsula sites are due to the particular dust transport pattern occurred over each station. Discrepancies between columnar-integrated and ground-level in-situ measurements show a clear dependence on height of the dust particle size distribution. Then, further vertical size-resolved observations are needed for evaluation of the impact on surface of the Saharan dust arrival to the Iberian Peninsula.

Download Full-text