Sea Breeze Circulation Research Articles

The Atmospheric Aerosol over Western Greece-Six Years of Aerosol Observations at the Navarino Environmental Observatory

The Eastern Mediterranean is a highly populated area with air quality problems. It is also where climate change is already noticed by higher temperatures and s changing precipitation pattern. The anthropogenic aerosol affects health and changing concentrations and properties of the atmospheric aerosol affect radiation balance and clouds. Continuous long-term observations are essential in assessing the influence of anthropogenic aerosols on climate and health. We present six years of observations from Navarino Environmental Observatory (NEO), a new station located at the south west tip of Peloponnese, Greece. The two sites at NEO, were evaluated to show the influence of the local meteorology and to assess the general background aerosol possible. It was found that the background aerosol was originated from aged European aerosols and was strongly influenced by biomass burning, fossil fuel combustion, and industry. When subsiding into the boundary layer, local sources contributed in the air masses moving south. Mesoscale meteorology determined the diurnal variation of aerosol properties such as mass and number by means of typical sea breeze circulation, giving rise to pronounced morning and evening peaks in pollutant levels. While synoptic scale meteorology, mainly large-scale air mass transport and precipitation, strongly influenced the seasonality of the aerosol properties.

Aerosol vertical distribution and interactions with land/sea breezes over the eastern coast of the Red Sea from lidar data and high-resolution WRF-Chem simulations

Abstract. With advances in modeling approaches and the application of satellite and ground-based data in dust-related research, our understanding of the dust cycle has significantly improved in recent decades. However, two aspects of the dust cycle, namely the vertical profiles and diurnal cycles, are not yet adequately understood, mainly due to the sparsity of direct observations. Measurements of backscattering caused by atmospheric aerosols have been ongoing since 2014 at the King Abdullah University of Science and Technology (KAUST) campus using a micro-pulse lidar (MPL) with a high temporal resolution. KAUST is located on the eastern coast of the Red Sea and currently hosts the only operating lidar system in the Arabian Peninsula. We use the data from the MPL together with other collocated observations and high-resolution simulations (with 1.33 km grid spacing) from the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to study the following three aspects of dust over the Red Sea coastal plains. Firstly, we compare the model-simulated surface winds, aerosol optical depth (AOD), and aerosol size distributions with observations and evaluate the model performance in representing a typical large-scale dust event over the study site. Secondly, we investigate the vertical profiles of aerosol extinction and concentration in terms of their seasonal and diurnal variability. Thirdly, we explore the interactions between dust aerosols and land/sea breezes, which are the most influential components of the local diurnal circulation in the region. The WRF-Chem model successfully reproduced the diurnal profile of surface wind speed, AOD, and dust size distributions over the study area compared to observations. The model also captured the onset, demise, and height of a large-scale dust event that occurred in 2015, as compared to the lidar data. The vertical profiles of aerosol extinction in different seasons were largely consistent between the MPL data and WRF-Chem simulations along with key observations and reanalyses used in this study. We found a substantial variation in the vertical profile of aerosols in different seasons and between daytime and nighttime, as revealed by the MPL data. The MPL data also identified a prominent dust layer at ∼5–7 km during the nighttime, which likely represents the long-range transported dust brought to the site by the easterly flow from remote inland deserts. The sea breeze circulation was much deeper (∼2 km) than the land breeze circulation (∼1 km), but both breeze systems prominently affected the distribution of dust aerosols over the study site. We observed that sea breezes push the dust aerosols upwards along the western slope of the Sarawat Mountains. These sea breezes eventually collide with the dust-laden northeasterly trade winds coming from nearby inland deserts, thus causing elevated dust maxima at a height of ∼1.5 km above sea level over the mountains. Moreover, the sea and land breezes intensify dust emissions from the coastal region during the daytime and nighttime, respectively. Our study, although focused on a particular region, has broader environmental implications as it highlights how aerosols and dust emissions from the coastal plains can affect the Red Sea climate and marine habitats.

Long Island enhanced aerosol event during 2018 LISTOS: Association with heatwave and marine influences.

The co-occurrence of enhancement in aerosol concentration, temperatures, and ozone mixing ratio was observed between June 29 and July 4, 2018 (enhanced period, EP) on Long Island (LI) and the greater NYC metropolitan area during part of the 2018 Long Island Sound Tropospheric Ozone Study (LISTOS). Two aerosol formation pathways were identified during the EP, the first being the condensation of semi- and intermediate volatility oxidation products of anthropogenic volatile organic compounds (AVOCs) under stagnant synoptic flow conditions, high temperatures and afternoon sea-breeze circulation. While this first pathway was prevalent, the most abundant organic aerosol factor was less oxidized oxygenated organic aerosol or LO-OOA. The second formation pathway occurred during a period of more persistent (synoptic) on-shore flow transporting more aged aerosol which consisted of an internal mixture of more oxidized oxygenated organic aerosol (MO-OOA), methanesulfonic acid (MSA) and sulfate. It was estimated that 35% of the sulfate observed during the mature period (an average of about 1.2μgm-3) originated from oceanic dimethyl sulfide (DMS) emissions. These two formation pathways helped elucidate the sources of fine particle pollution, highlighted the interaction between human emissions and natural DMS emission, and will help our understanding of pollution affecting other urban areas adjacent to large bodies of water during hot and stagnant periods.

Monsoons, ITCZs, and the Concept of the Global Monsoon

AbstractEarth's tropical and subtropical rainbands, such as Intertropical Convergence Zones (ITCZs) and monsoons, are complex systems, governed by both large‐scale constraints on the atmospheric general circulation and regional interactions with continents and orography, and coupled to the ocean. Monsoons have historically been considered as regional large‐scale sea breeze circulations, driven by land‐sea contrast. More recently, a perspective has emerged of a global monsoon, a global‐scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation. This results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone. Regional subsystems are embedded in this global monsoon, localized by surface boundary conditions. Parallel with this, much theoretical progress has been made on the fundamental dynamics of the seasonal Hadley cells and convergence zones via the use of hierarchical modeling approaches, including aquaplanets. Here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings. After summarizing the dynamical and energetic balances that distinguish an ITCZ from a monsoon, we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets. Limitations of current theories are discussed, including the need for a better understanding of the influence of zonal asymmetries and transients on the large‐scale tropical circulation.

Urbanization-induced land and aerosol impacts on sea-breeze circulation and convective precipitation

Abstract. Changes in land cover and aerosols resulting from urbanization may impact convective clouds and precipitation. Here we investigate how Houston urbanization can modify sea-breeze-induced convective cloud and precipitation through the urban land effect and anthropogenic aerosol effect. The simulations are carried out with the Chemistry version of the Weather Research and Forecasting model (WRF-Chem), which is coupled with spectral-bin microphysics (SBM) and the multilayer urban model with a building energy model (BEM-BEP). We find that Houston urbanization (the joint effect of both urban land and anthropogenic aerosols) notably enhances storm intensity (by ∼ 75 % in maximum vertical velocity) and precipitation intensity (up to 45 %), with the anthropogenic aerosol effect more significant than the urban land effect. Urban land effect modifies convective evolution: speed up the transition from the warm cloud to mixed-phase cloud, thus initiating surface rain earlier but slowing down the convective cell dissipation, all of which result from urban heating-induced stronger sea-breeze circulation. The anthropogenic aerosol effect becomes evident after the cloud evolves into the mixed-phase cloud, accelerating the development of storm from the mixed-phase cloud to deep cloud by ∼ 40 min. Through aerosol–cloud interaction (ACI), aerosols boost convective intensity and precipitation mainly by activating numerous ultrafine particles at the mixed-phase and deep cloud stages. This work shows the importance of considering both the urban land and anthropogenic aerosol effects for understanding urbanization effects on convective clouds and precipitation.

The semi-diurnal cycle of deep convective systems over Eastern China and its surrounding seas in summer based on an automatic tracking algorithm

Deep convective systems (DCSs) are associated with severe weather events and can affect regional and global climate. To study the semi-diurnal variation of DCSs over Eastern China and its surrounding seas in summer, we modified the Tracking of Organized Convection Algorithm through a 3-D segmentatioN (TOOCAN) by employing Himawari-8 operational cloud property (CLP) products instead of original infrared images, and renamed the algorithm as TOOCAN-CLP. The DCSs detected over land and sea are divided into small-, medium-, and large-sized classes based on the convective core equivalent radius. The small and medium-sized DCSs over land exhibit a maximum occurrence in the afternoon, which is associated with local thermal instability and sea breeze circulation. The occurrence of small DCSs over the tropical sea areas varies analogously to that of small continental DCSs but with a smaller amplitude. However, medium-sized DCSs over the sea, which account for the majority of DCSs over the sea, exhibit weak semi-diurnal variability. Large DCSs over inland China and its surrounding seas tend to initiate at night and decay in the daytime. The generation of large DCSs over inland China at night is mainly due to the enhanced transport of warm and moist air by strong large-scale prevailing southerly or southwesterly winds, while the large offshore DCSs accompanied by heavy rainfall is closely associated with the interaction between local offshore breeze and large-scale monsoon flows, as well as gravity waves.

Urban and ecological prerequisites for the development of the Black Sea cities in the Krasnodar region with consideration of thermal and wind processes

Introduction. Ecology of the atmospheric environment of coastal cities directly depends on the thermal and wind processes, which are formed by irradiation of the active city surface and slope mountain areas adjacent to the city, as well as the sea area. Materials and methods. The study is based on a comprehensive methodology for studying urban and ecological processes of the atmospheric environment at the macro- and mesoecological level of urban planning. Modern computer models ICON, GFS and GEM utilized in applied meteorology were used, as well as the semi-graphical method of modeling daily pollution dome transformation based on thermophysical and aerodynamic laws of atmospheric environment and irradiation of the building’s active surface and of the surrounding landscape. Results. The transformation and movement chart of the air pollution dome formed over the city during the day in the “mountains – city – sea” system is presented. It is proved that in the warm season in the first half of the day, the maximum accumulation zone of negative atmospheric pollutants is located in the mountain foothills facing east, by mid-day it will be shifted to the center of the city, and in the evening the maximum pollution will be observed in the coastal zone. The presented ecological efficiency in urban planning on the example of the Black Sea cities of Novorossiysk and Tuapse allows for the assessment of the thermal and wind process impact on the transformation and movement of atmospheric pollution dome in complex terrain and sea area conditions using the assessment classification of “satisfactory” in the first half of the day, “good” in the day and evening. Conclusions. The research is particularly relevant in southern cities located on the coast and bordering the mountainous territory. The main urban and ecological principle of planning organization in the reconstruction, planning and development of coastal cities and towns is the mechanism of thermodynamic and aerodynamic processes of the atmospheric environment, expressed in the form of sea breeze and mountain-valley circulation, as well as convective flows, the study of which allowed to formulate practical recommendations.

Numerical simulation of land and sea-breeze (LSB) circulation along the Guinean Coast of West Africa

This study uses both observed and simulated data to investigate the diurnal evolution of land and sea-breeze (LSB) circulation across the Guinean Coast of West Africa. Numerical simulations, with ERA-Interim and CFS as forcing data, were carried out using a modified WRF-ARW model code to evaluate the model’s ability to capture the LSB kinematics over West Africa. Two simulation runs were performed with each data set. Comparison of the simulated and observed winds showed that the WRF model was able to capture the rotation of LSB in the coastal areas of the region very well. Results also showed that the simulated diurnal evolutions of the hodographs and onshore/offshore winds were found to be in good agreement with the observations. Furthermore, the simulations showed complex patterns of clockwise (CR) and anti-clockwise rotations (ACR) across the Guinean Coast. The sense of rotation is a result of complex interaction between surface and synoptic pressure gradients, horizontal and vertical diffusion, and advection terms. Overall, the results of the analysis showed that the balance is not always dominated by the pressure gradient terms, as suggested by earlier studies. However, hourly analysis of the rotation terms strongly indicates that over the ocean, surface pressure gradients dominate, while diffusion terms are more important over land areas. The Coriolis term was found not to be significant, the study area being close to the equator. Significantly, regions over water are found to be dominated by ACR, while land areas showed more CR. This may be attributed to the variation of surface roughness due to the landscape and urbanization.

Metodologia preliminar de identificação de relações entre a brisa marítima e linhas de instabilidade amazônicas

The objective of this work was to present a preliminary methodology that is able to identify some characteristics of the relationship between the sea breeze circulation and the Amazonian squalline, aiming to understand a little more of the necessary conditions for the deepening of the associated cloudiness. The wavelet transform was applied to the wind and divergence data of ERA5 reanalysis, and a classification was afterwards developed to highlight exclusively the days considered the ideal active period to formation and intensification of the sea breeze circulation and initiation of the Amazonian squalline. The results showed that the relationship between the sea breeze circulation and the Amazonian squalline may be related to the influence of wind at 800 hPa and divergence at 200 hPa. The analysis of average field of the active period days ideal for formation and intensification of the sea breeze circulation and initiation of the Amazonian squalline was able to represent important wind-related characteristics (low level jet between 850 and 750 hPa) and divergence at 200 hPa, indicating that these characteristics, before being directly related to the Amazonian squalline, may first influence the sea breeze circulation performance and intensification.

Estimativa da altura da camada limite planetária no Centro de Lançamento de Alcântara

Sea and land breeze circulation and the internal boundary layer are some aspects that make it difficult to determine the coastal Planetary Boundary Layer (PBL) height (h). This paper evaluates the h estimation for the Alcantara Launch Center (CLA) in Maranhão state using 14 months of remote measurements obtained by a ceilometer and by the ERA5 reanalysis. This response depends on the concentration of aerosols and atmospheric humidity present. Mean results indicated that dry months (September to November, with = 637 488 m) tend to have less hourly and seasonal variability of h compared to wet months (March to May, with = 770 912 m). A higher mean error in the wet season was obtained with ERA5 PBL h (h = 708 53 m over the land; e h = 648 46 m over the ocean) than in the dry season (h = 18 89 m; e h = 46 77 m). The greater amount of atmospheric humidity during the rainy season increases the estimation uncertainty. This condition was more frequent at night due to typical rainfall in the place.

Consistent dust electrification from Arabian Gulf sea breezes

The Arabian Gulf region experiences regular thermally driven sea breeze circulations which occur all year round, penetrating hundreds of kilometres inland. As a sea breeze front moves inland, substantial electric fields are generated by separation of charged desert dust. In the first surface electric field measurements made in the United Arab Emirates (UAE), consistent and repeatable substantial electric field changes with magnitudes up to 7 kV m−1 have been detected at Al Ain (170 km from the western coast), during 80 separate sea breeze events in 2018. Every sea breeze frontal passage shows the same characteristic signature of a transient maximum peak in electric field lasting tens of minutes. Electric field changes during these events were always negative (i.e. enhancing the existing negative ‘fair weather’ electric field), in contrast to many other reported observations in dust storms in which conditions were less repeatable. The regular and substantial dust electrification found demonstrates that accurate representation of dust in climate and weather models requires electrical effects to be addressed, both in the generation process, and by considering aggregates in radiative transfer calculations as electrically aligned rather than randomly ordered. Furthermore, satellite aerosol retrievals are affected by the changed attenuation of electromagnetic radiation when dust particles are charged, for which corrections may be needed.

Tracking the atmospheric pulse of a North American megacity from a mountaintop remote sensing observatory

Atmospheric carbon monoxide (CO) is an effective tracer for monitoring atmospheric transport processes and for detecting pollution sources of anthropogenic origin. However, very few observation systems exist that are capable of providing measurements with high spatial and temporal resolution to identify hotspots for emission control purposes. Here we introduce a mountain-top remote sensing observatory, the California Laboratory for Atmospheric Remote Sensing (CLARS), for mapping the enhancement of CO column-averaged mixing ratio (XCO) over the Los Angeles (LA) megacity. Compared to conventional observation network, CLARS is unique in the following ways: (1) it mimics a geostationary satellite observatory for LA with approximately hourly- and kilometer-scale mapping capability; (2) the free tropospheric background atmosphere is simultaneously measured; and (3) the measurements are highly sensitive to anthropogenic emissions due to the long light path along the planetary boundary layer (PBL). The CO slant column density and XCO are retrieved from reflected sunlight measurements in the 2.3 μm CO band and the 1.27 μm oxygen (O2) band. Data filtering and corrections for aerosol scattering and geometric effects are then implemented to derive the XCO enhancement, which is the XCO excess in the PBL compared to the background value. In the LA megacity, the XCO enhancement shows a distinctive diurnal cycle primarily driven by changes in anthropogenic emissions and sea-breeze circulation. Such diurnal patterns can be reproduced by the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). The enhancement also shows a significant weekly cycle resulting from the weekly pattern in anthropogenic CO emissions. On average, the XCO enhancements on Sunday and Saturday are 16.1% and 4.4%, respectively, lower than weekday values. The weekly XCO enhancement patterns also show high correlation with traffic counts. A seasonal pattern of XCO enhancement with high (low) spatial contrast in summer (winter), resulting from changing sea-breeze circulation, can be observed. These diurnal, weekly, and seasonal patterns of XCO enhancement serve as tracers of the atmospheric pulse of the LA megacity. The CLARS observatory can serve as a testbed for future geostationary missions to track anthropogenic emissions in cities.

Response times of meteorological air temperature sensors

AbstractGuidelines in the Guide to Meteorological Instruments and Methods of Observation (the CIMO guide) of the World Meteorological Organization (WMO, published 2014, updated 2017, section 2.1.3.3, Response times of thermometers) recommend that the 63% response time τ for an air temperature sensor be 20 s, although – as airflow speed influences response time – the minimum airflow speed at which this applies should also be specified in the document. A 63% response time τ63 = 20 s implies that 95% of a step change be registered within 3τ63 or 60 s, the WMO recommended averaging interval for air temperature: rapid air temperature changes on this time‐scale are not uncommon, often associated with convective squalls, frontal systems or sea breeze circulations. An alternative way of expressing the effect of the time constant is that in air whose temperature is changing at 0.1 K·min−1 the thermometer would lag by approximately 0.03 K.To assess whether this response time specification was realistic, we have undertaken an experimental and theoretical study of the time constants of meteorological thermometers. Laboratory wind tunnel tests were undertaken to quantify 63% and 95% response times of 25 commercial 100 Ω platinum resistance thermometers (PRTs) of various sizes (length and sheath diameter) from five manufacturers. The test results revealed a fourfold difference in response times between different sensors: none of the PRTs tested met the CIMO response time guideline at a ventilation speed of 1 m·s−1 assumed typical of passively ventilated thermometer shields such as Stevenson‐type thermometer screens. A theoretical model of the sensors was devised which matched the experimental behaviour with regard to the most important contributing factors, namely ventilation rate and sensor diameter. Finally, suggestions and recommendations for operational air temperature sensor adoption and future sensor development are included.

Urban heat island circulations over the Beijing-Tianjin region under calm and fair conditions

The Beijing-Tianjin-Hebei region has experienced severe urban heat island (UHI) effects in recent decades. Using the Weather Research and Forecasting (WRF) model and the new World Urban Database and Access Portal Tools (WUDAPT) land-use dataset, the urban heat island circulations (UHICs) and other local atmospheric circulations over Beijing and Tianjin were studied during a severe UHI event in 2012. It was shown that in the daytime, various UHICs over Beijing and Tianjin developed separately under a southerly background wind. Two of these UHICs formed over Beijing due to multiple hot regions, involving a chain flow mechanism in which the outflows from one UHIC over nearby mountains were connected to the inflows to the other UHICs in a west-to-east direction. At night, more robust UHICs occurred and a chain flow mechanism again formed over the Beijing-Tianjin region, as the upper-level outflows from the UHIC over Tianjin were connected to the inflows of the UHIC over Beijing. Moreover, the rotary air movements formed by the flows over the mountain and the down-slope winds formed a convergent region in the northwest of Beijing. In particular, sensitivity experiments replacing either Beijing or Tianjin with cropland grids revealed that the presence of either of those urban areas modified the penetration of the sea-breeze circulation. The city shape was found to affect the UHIC over Beijing at night, as the convergent zones were distributed diagonally and the wind speeds were higher in the diagonal direction.

Air-sea interactions on Titan: Lake evaporation, atmospheric circulation, and cloud formation

Titan's abundant lakes and seas exchange methane vapor and energy with the atmosphere via a process generally known as air-sea interaction. This turbulent exchange process is investigated with an atmospheric mesoscale model coupled to a slab model representation of an underlying lake. The impact of lake size, effective lake mixed layer depth, background wind speed, air-lake temperature differential, and atmospheric humidity on air-sea interaction processes is studied through dozens of two-dimensional simulations. The general, quasi-steady solution is a non-linear superposition of a very weak background plume circulation driven by the buoyancy of evaporated methane with a stronger opposing thermally direct (sea breeze) circulation driven by the thermal contrast between the cold marine layer over the lake and the warmer inland air. The specific solution depends on the value of selected atmosphere and lake property parameters, but the general solution of the superposition of these two circulations is persistent. Consistent with previous analytical work of others, the sensible heat flux and the latent heat flux trend toward opposite and equal values such that their ratio, the Bowen ratio, approaches −1.0 in most, but not all, of the quasi-steady state solutions. Importantly, in nearly all scenarios, the absolute magnitude of the fluxes trends toward very small values such that the equilibrium solution is also nearly a trivial solution where air-sea energy exchange is ~3 W m−2 or less. In all cases, a cool, moist, and statically stable shallow marine layer with nearly calm winds and small turbulent flux exchanges with a colder underlying lake is produced by the model. The temperature of the lake, the marine properties of the air, and the strength of the sea breeze depends on the initial conditions and to a lesser degree, the boundary conditions.

Mobile Laboratory Measurements of High Surface Ozone Levels and Spatial Heterogeneity During LISTOS 2018: Evidence for Sea Breeze Influence

AbstractThe Long Island Sound Tropospheric Ozone Study (LISTOS) was organized to investigate ozone formation and transport in the New York City metropolitan area and locations downwind. During LISTOS, the University at Albany Atmospheric Sciences Research Center (ASRC) mobile laboratory was used for measuring surface O3, NO2, and aerosol number and mass concentration. Sharp O3 concentration gradients, with ΔO3 Δy−1 over 15 ppb km−1, were measured both at and near the land‐water interface and on the highway on days characterized by high regional O3 concentrations. These large O3 gradients at or near the land‐water interface, and in air masses relatively low in NO2, are shown to be influenced in part by the transport of highly oxidized air masses via sea breeze circulation and convergence with gradient flow. On the highway under regionally high O3 concentrations, strong anticorrelation (R2 = 0.78, p < 0.05) between O3 and NO2 and an absolute slope less than 1 suggested that Ox concentrations (O3 + NO2) increased with increasing NO2. Overall, the on‐road measurements made during LISTOS help to better characterize the interaction between the emitted pollution and the meteorological conditions on Long Island, thereby having potential policy implications.

Hygroscopic properties and cloud condensation nuclei activity of atmospheric aerosols under the influences of Asian continental outflow and new particle formation at a coastal site in eastern Asia

Abstract. The chemical composition of fine particulate matter (PM2.5), the size distribution and number concentration of aerosol particles (NCN), and the number concentration of cloud condensation nuclei (NCCN) were measured at the northern tip of Taiwan during an intensive observation experiment from April 2017 to March 2018. The parameters of aerosol hygroscopicity (i.e., activation ratio, activation diameter and kappa of CCN) were retrieved from the measurements. Significant variations were found in the hygroscopicity of aerosols (kappa – κ – of 0.18–0.56, for water vapor supersaturation – SS – of 0.12 %–0.80 %), which were subject to various pollution sources, including aged air pollutants originating in eastern and northern China and transported by the Asian continental outflows and fresh particles emitted from local sources and distributed by land–sea breeze circulations as well as produced by processes of new particle formation (NPF). Cluster analysis was applied to the back trajectories of air masses to investigate their respective source regions. The results showed that aerosols associated with Asian continental outflows were characterized by lower NCN and NCCN values and by higher kappa values of CCN, whereas higher NCN and NCCN values with lower kappa values of CCN were observed in the aerosols associated with local air masses. Besides, it was revealed that the kappa value of CCN exhibited a decrease during the early stage of an event of new particle formation, which turned to an increasing trend over the later period. The distinct features in the hygroscopicity of aerosols were found to be consistent with the characteristics in the chemical composition of PM2.5. This study has depicted a clear seasonal characteristic of hygroscopicity and CCN activity under the influence of a complex mixture of pollutants from different regional and/or local pollution sources. Nevertheless, the mixing state and chemical composition of the aerosols critically influence the aerosol hygroscopicity, and further investigations are necessary to elucidate the atmospheric processing involved in the CCN activation in coastal areas.

Numerical Modeling for the Accidental Dispersion of Hazardous Air Pollutants in the Urban Metropolitan Area

A numerical simulation system is developed to predict the dispersion of hazardous air pollutants (HAPs) over a populated city due to accidental release. Ulsan, as one of the megacities in Korea, is chosen as an ideal testbed for the simulation, as it is located in complex terrain and hosts a national industrial complex on the outskirts of the city. The system is based on the California puff model (CALPUFF) for simulating a HAP’s dispersion, in which the three-dimensional atmospheric circulation derived from the observed weather station data is specified at a fine horizontal resolution of 200 m. A test scenario is developed for the accidental release of benzene during the daytime and nighttime, respectively, by a fictitious explosion of a storage container, and the injection amount is determined arbitrarily yet comparable to those in the past accidents. In attempting a quantitative assessment and zoning the level of potential risk over the impacted area, multiple simulations have been conducted each day with different hourly varying meteorological conditions in August. The dispersion characteristics of the air pollutant depend largely on the local wind patterns that vary substantially from day to day. Nevertheless, the composite analysis sufficiently identifies the impacted area by the HAP’s dispersion due to the local prevailing wind such as the land–sea breeze circulation. An immediate hazardous area is determined based on the vulnerability map constructed by zoning the level of risk determined by the spatial distribution of the HAPs’ concentration and the harmfulness standard to the human body.

A multi-scale model analysis of ozone formation in the Bangkok Metropolitan Region, Thailand

Abstract Over the last three decades, Thailand's rapid industrialization and urbanization have led to an impact on urban air quality. A majority of the country's development has occurred within and around Bangkok (BKK), the capital city of Thailand, and the Bangkok Metropolitan Region (BMR). Since 1995, the BMR has experienced air quality degradation, in particular, enhanced ozone (O3) due to a combination of the local increase in emissions from accelerated growth in automotive and industrial activities, local meteorology including strong solar radiation, high temperature and high humidity, and potential long-range effects of regional transport from China. To investigate the O3 formation in the BMR due to the effects of long-range transport and local meteorology feedbacks, we perform a multi-scale simulation with the Weather Research and Forecasting model with Chemistry (WRF-Chem) during the O3 season (January to March), 2010; since O3 mixing ratio exceedances in the BMR occur primarily during this period The results in this study indicate the significance of China's emission reductions on the regional-scale and the local-scale pollution, as far as the BMR region and southern Thailand. Applying China's oxide of nitrogen (NOx)-only emission controls, generally, enhance the domain-wide monthly-average peroxyacetyl nitrate (PAN) and O3 in the regional scale, in the order of ~1–7% and ~1–5%, respectively, while those in the local scale are ~ 0.2–6% and ~0.1–5% compared with the baseline simulation. However, the increases in PAN and O3 are mitigated by 40% China's Volatile Organic Compound (VOC) reduction along with 40% NOx reduction. The results, supported by an indicator analysis, suggest that northern and eastern China, northern and central Thailand and the BMR, are likely VOC-limited during the O3 season. Since the BMR is VOC-limited regime, controlling anthropogenic VOC emissions will show more benefit to control O3 than controlling NOx-only emissions. Other factors that influence on O3 levels in the BMR are biogenic VOC emissions from the Tenasserim range and land- and sea-breeze circulations that recirculate and disperse pollutants along the coastal areas.

Impact of land surface physics in WRF on the simulation of sea breeze circulation over southeast coast of India

In this work, the impact of land surface physics in simulating the sea and land breeze circulation along the south east coast of India near Kalpakkam is studied using the Weather Research and Forecasting (WRF) model for emergency response application. Simulations were conducted with three different land surface models (LSMs)—5-Layer soil thermal diffusion scheme (5-Layer), Noah land surface model (Noah) and Noah Multi-Physics land surface model (Noah-MP) for different days in summer and southwest monsoon. Observations from meteorological towers, automated weather stations, sonic anemometers and GPS Radiosonde profiles were used for comparison. Results indicate that the Noah-MP followed by Noah schemes produce more realistic simulations of the sea breeze circulation in terms of intensity, onset time, duration, horizontal and vertical extents in most of the studied cases compared to the 5-Layer scheme. Results indicate that the 5-Layer model grossly overestimated air temperature, heat flux and boundary layer height relative to Noah and Noah-MP schemes. The Noah-MP scheme better represented the land-surface feedback in terms of soil temperature, skin temperature and surface energy fluxes leading to more realistic simulations of sea breeze and boundary layer characteristics.