Recirculation Of Pollutants Research Articles

River winds and pollutant recirculation near the Manaus city in the central Amazon

Local atmospheric recirculation flows (i.e., river winds) induced by thermal contrast between wide Amazon rivers and adjacent forests could affect pollutant dispersion, but observational platforms for investigating this possibility have been lacking. Here we collected daytime vertical profiles of meteorological variables and chemical concentrations up to 500 m with a copter-type unmanned aerial vehicle during the 2019 dry season. Cluster analysis showed that a river-forest recirculation flow occurred for 23% (13 of 56) of the profiles. In fair weather, the thermally driven river winds fully developed for synoptic wind speeds below 4 m s−1, and during these periods the vertical profiles of carbon monoxide and total oxidants (defined as ozone and nitrogen dioxide) were altered. Numerical modeling shows that the river winds can recirculate pollution back toward the riverbank. There are implications regarding air quality for the many human settlements along the rivers throughout northern Brazil.

Evaluation of NASA's high-resolution global composition simulations: Understanding a pollution event in the Chesapeake Bay during the summer 2017 OWLETS campaign

Recirculation of pollutants due to a bay breeze effect is a key meteorological mechanism impacting air quality near urban coastal areas, but regional and global chemical transport models have historically struggled to capture this phenomenon. We present a case study of a high ozone (O3) episode observed over the Chesapeake Bay during the NASA Ozone Water-Land Environmental Transition Study (OWLETS) in summer 2017. OWLETS included a complementary suite of ground-based and airborne observations, with which we characterize the meteorological and chemical context of this event and develop a framework to evaluate model performance. Two publicly-available NASA global high-resolution coupled chemistry-meteorology models (CCMMs) are investigated: GEOS-CF and MERRA2-GMI. The GEOS-CF R2 value for comparisons between the NASA Sherpa C-23 aircraft measurements to the GEOS-CF resulted in good agreement (R2: 0.67) on July 19th and fair agreement (R2: 0.55) for July 20th. Compared to surface observations, we find the GEOS-CF product with a 25 × 25 km2 grid box, at an hourly (R2: 0.62 to 0.87) and 15-min (R2: 0.64 to 0.87) interval for six regional sites outperforms the hourly nominally 50 × 50 km2 gridded MERRA2-GMI (R2: 0.53 to 0.76) for four of the six sites, suggesting it is better capable of simulating complex chemical and meteorological features associated with ozone transport within the Chesapeake Bay airshed. When the GEOS-CF product was compared to the TOLNet LiDAR observations at both NASA Langley Research Center (LaRC) and the Chesapeake Bay Bridge Tunnel (CBBT), the median differences at LaRC were −6 to 8% and at CBBT were ±7% between 400 and 2000 m ASL. This indicates that, for this case study, the GEOS-CF is able to simulate surface level ozone diurnal cycles and vertical ozone profiles at small scales between the surface level and 2000 m ASL. Evaluating global chemical model simulations at sub-regional scales will help air quality scientists understand the complex processes occurring at small spatial and temporal scales within complex surface terrain changes, simulating nighttime chemistry and deposition, and the potential to use global chemical transport simulations in support of regional and sub-regional field campaigns.

Improved meteorology and ozone air quality simulations using MODIS land surface parameters in the Yangtze River Delta urban cluster, China

AbstractLand surface parameters play an important role in the land‐atmosphere coupling and thus are critical to the weather and dispersion of pollutants in the atmosphere. This work aims at improving the meteorology and air quality simulations for a high‐ozone (O3) event in the Yangtze River Delta urban cluster of China, through incorporation of satellite‐derived land surface parameters. Using Moderate Resolution Imaging Spectroradiometer (MODIS) input to specify the land cover type, green vegetation fraction, leaf area index, albedo, emissivity, and deep soil temperature provides a more realistic representation of surface characteristics. Preliminary evaluations reveal clearly improved meteorological simulation with MODIS input compared with that using default parameters, particularly for temperature (from −2.5 to −1.7°C for mean bias) and humidity (from 9.7% to 4.3% for mean bias). The improved meteorology propagates through the air quality system, which results in better estimates for surface NO2 (from 11.5 to 8.0 ppb for mean bias) and nocturnal O3 low‐end concentration values (from −18.8 to −13.6 ppb for mean bias). Modifications of the urban land surface parameters are the main reason for model improvement. The deeper urban boundary layer and intense updraft induced by the urban heat island are favorable for pollutant dilution, thus contributing to lower NO2 and elevated nocturnal O3. Furthermore, the intensified sea‐land breeze circulation may exacerbate O3 pollution at coastal cities through pollutant recirculation. Improvement of mesoscale meteorology and air quality simulations with satellite‐derived land surface parameters will be useful for air pollution monitoring and forecasting in urban areas.

Measurements of the aerosol chemical composition and mixing state in the Po Valley using multiple spectroscopic techniques

Abstract. The use of co-located multiple spectroscopic techniques can provide detailed information on the atmospheric processes regulating aerosol chemical composition and mixing state. So far, field campaigns heavily equipped with aerosol mass spectrometers have been carried out mainly in large conurbations and in areas directly affected by their outflow, whereas lesser efforts have been dedicated to continental areas characterised by a less dense urbanisation. We present here the results obtained at a background site in the Po Valley, Italy, in summer 2009. For the first time in Europe, six state-of-the-art spectrometric techniques were used in parallel: aerosol time-of-flight mass spectrometer (ATOFMS), two aerosol mass spectrometers (high-resolution time-of-flight aerosol mass spectrometer – HR-ToF-AMS and soot particle aerosol mass spectrometer – SP-AMS), thermal desorption aerosol gas chromatography (TAG), chemical ionisation mass spectrometry (CIMS) and (offline) proton nuclear magnetic resonance (1H-NMR) spectroscopy. The results indicate that, under high-pressure conditions, atmospheric stratification at night and early morning hours led to the accumulation of aerosols produced by anthropogenic sources distributed over the Po Valley plain. Such aerosols include primary components such as black carbon (BC), secondary semivolatile compounds such as ammonium nitrate and amines and a class of monocarboxylic acids which correspond to the AMS cooking organic aerosol (COA) already identified in urban areas. In daytime, the entrainment of aged air masses in the mixing layer is responsible for the accumulation of low-volatility oxygenated organic aerosol (LV-OOA) and also for the recycling of non-volatile primary species such as black carbon. According to organic aerosol source apportionment, anthropogenic aerosols accumulating in the lower layers overnight accounted for 38% of organic aerosol mass on average, another 21% was accounted for by aerosols recirculated in residual layers but still originating in northern Italy, while a substantial fraction (41%) was due to the most aged aerosols imported from transalpine areas. The different meteorological regimes also affected the BC mixing state: in periods of enhanced stagnation and recirculation of pollutants, the number fraction of the BC-containing particles determined by ATOFMS was 75% of the total, while in the days of enhanced ventilation of the planetary boundary layer (PBL), such fraction was significantly lower (50%) because of the relative greater influence of non-BC-containing aerosol local sources in the Po Valley. Overall, a full internal mixing between BC and the non-refractory aerosol chemical components was not observed during the experiment in this environment.

Linking particle number concentration (PNC), meteorology and traffic variables in a UK street canyon

Ambient particle number concentration (PNC) has been linked with adverse health outcomes such as asthma, reduced lung function and cardiovascular disease. To investigate the relationship between PNC, meteorology and traffic we measured size segregated respirable particles in a busy commuter street in Swansea, UK for ten months using a Dekati Electrical Low Pressure Impactor (ELPI). The ELPI segregates particles into 12 size fractions between 7nm and 10μm. The median PNC for the sampling period was 31,545cm−3. For the ultrafine particles (7–93nm), the highest PNC was found in winter (46,615cm−3; 15minute average) and the lowest for that size fraction in summer (29,696cm−3). For the particles below 93nm there was a trimodal distribution to weekdays (particularly Monday to Wednesday), with PNC peaks at 09:00, 16:00 and 23:00. Wind direction had a significant influence on PNC and differed between particles in the fine range (below 2.5μm) and more coarse particles (up to 10μm). For fine particles, winds parallel to the canyon were associated with higher PNCs which were attributed to the replenishment of traffic particles. For coarse particles, PNCs were higher from winds perpendicular to the canyon and this was linked to source distribution around the sampling site and the recirculation of pollutants within the canyon. During times when vehicle volumes were high and vehicles were exhibiting stop–start behaviour, if this was combined with low wind speeds, ultrafine PNC was highest. This effect was generally observed during the morning rush hour. Current mass-based legislation does not take into account exposure to the number of particles or the change in population exposure diurnally.

Atmospheric dynamics and elevated ozone concentrations in the northern Adriatic

ABSTRACTThe influence of mesoscale flow on the elevated O3concentrations recorded during 13–19 August 2000 in the coastal town of Rijeka (45.33°N, 14.45°E) has been examined. Although high levels of ozone concentration are often observed there, this episode was unique due to hourly afternoon concentrations persistently higher than 180 µg m−3and nocturnal levels above 100 µg m−3. To study this episode, available meteorological and ozone measurements were analysed, along with supplemental numerical simulations and trajectories. The measurements revealed favourable atmospheric conditions for the production of ozone, i.e., high air temperatures associated with (1) the exchange of two dominant (although relatively weak) large‐scale flows: southwesterlyversusnortheasterly bora winds, and (2) local thermal circulation. The bora wind was relatively weak and short lasting. Although the bora transported the polluted air mass away along the western Adriatic coast, the southwesterly flow returned ozone‐rich air toward the Alps, thus contributing to the overall pollution over the northern Adriatic Sea. Models revealed the superposition of the southwesterly wind and local, thermally induced winds that caused the regional transport of ozone toward the Alps and the eastern Adriatic coast. However, while the regional transport of ozone from the northern Adriatic was found to enhance somewhat the ozone concentrations in Rijeka at the end of period studied, its surrounding local emission sources, uniform local thermal circulation systems, and recirculation of pollutants were crucial factors in the formation of the large daytime and night time ozone levels observed in Rijeka.

Diurnal cycle of air pollution in the Kathmandu Valley, Nepal: Observations

During the dry season of 2004–2005 we carried out field measurements of air pollution and meteorology in the Kathmandu Valley, Nepal, a bowl‐shaped urban basin in the Himalayan foothills of Nepal. We measured the trace gases carbon monoxide (CO) and ozone (O3) and particulates (PM10), as well as meteorological variables. In our field observations we noted a very regular pattern of morning and evening peaks in CO and PM10 occurring daily in the valley bottom, interspersed with low values in the afternoons and at night. This pattern occurred even on days with unusual timing of emissions and was influenced by the timing of ventilation from the valley. Meteorological variables showed great day‐to‐day similarity, with a strong westerly wind blowing through the valley from late morning until dusk. We found that the air mass on nearby mountaintops was disconnected from pollution within the valley during the night, but received significant pollution during the morning, when up‐slope flows began. At a pass on the western edge of the valley we found a diurnal switch in wind direction, with an inflow from late morning until late evening, and an outflow during the rest of the time. We found that part of the morning peak in pollution was caused by recirculation of pollutants emitted the night before, which spend the night in elevated layers over the valley.

MM5-CAMx를 이용한 대기오염물질의 재순환현상 모델링: 2004년 6월 수도권 오존오염 사례연구

Recent evidence has demonstrated that the pollutant recirculation can play an important role in leading to high ozone concentrations. In this study, the MM5-CAMx air quality modeling system was applied to simulate the pollutant recirculation and identify the transport of pollution during the high event (the maximum of 195 ppb) observed in the Greater Seoul Area (GSA) on June in 2004. The results showed a weak northeasterly synoptic wind during the night and early morning moved the air parcels containing the locally emitted urban pollution to the coast, which contributed to enhance formation in the southwest part of the GSA. As the sea breeze developed and started to penetrate inland in the late afternoon, the rapid build-up of concentration was found in the southwest coastal area due to the recirculation of the polluted air loaded with high level . The simulated backward trajectories and observations at coastal sites confirmed the recirculation of pollutant with the late sea breeze is the dominant factor affecting the occurrence of high concentrations in the southwestern GSA.

Daytime and nighttime aircraft lidar measurements showing evidence of particulate matter transport into the Northeastern valleys of the Lower Fraser Valley, BC

As part of the Pacific 2001 Air Quality Field Study a simultaneous upward/downward airborne lidar system called AERIAL (AERosol Imaging Airborne Lidar) operating at the fundamental Nd:YAG wavelength, 1064 nm, was flown aboard the National Research Council of Canada Convair 580 (CV580). The primary task of this platform was to establish a regional picture of particulate matter (PM) concentrations in the Lower Fraser Valley (LFV). The high temporal and spatial resolution of the lidar, provided images of PM stratification and boundary layer structure along predetermined flight lines. The flight lines were divided into a series of north–south and east–west lines to provide a snapshot of the LFV as well as provide aerial support for three main ground sites. The airborne lidar system also included a cross-polarization channel that is sensitive to particle shape (non-sphericity), for example smoke plumes from forest fires. There were nine flights flown over a 3-week period including two night flights. Comparing AERIAL results on the 26 and 29 August, between the afternoon and nighttime, showed increased PM concentrations in the Northeastern tributary valleys during the night flights due to a persistent sea breeze signal on both days. The complexity of the LFV airshed was further evidenced by the re-circulation of pollutants through upslope advection. The spatial and temporal variation of the planetary boundary layer height was also shown to play an important role in the air quality of the region.

Recirculation of coastal urban air pollution under a synoptic scale thermal trough in Perth, Western Australia

Air pollutant recirculation is a common feature of coastal cities as a result of the diurnal variation of the land/sea breeze circulation. On the western coast of Australia, a thermally induced synoptic scale trough interacts with this local circulation to enhance the sea breeze flow, allowing pollutant to penetrate further inland. As well a low wind speed zone formed offshore near the trough axis leads to increased ozone concentrations and the rotation of the trough axis during its onshore movement spreads these higher concentrations of air pollutant over a larger area.

Aspects of atmospheric flow and dispersion of air pollutants in a mountainous basin

The variety of physicogeographic characteristics, the complex topography and channeling of the synoptic/regional flow are among the main reasons for the formulation of local flow patterns, and consequently for the dispersion conditions in a mountainous area. In this paper, an attempt is made to investigate the mechanisms responsible for these phenomena and to explain the dispersion of air pollutants in a mountainous basin, especially the impingement of plumes released by elevated stacks. A coupled atmospheric and Lagrangian dispersion model was used for the analysis. As it was found significant, mesoscale circulation, such as lake effects in mountainous terrain, up/downslope and valley winds, was calculated. It was proved that the plume impingement, along with pollutant recirculation, could explain the nighttime maximum air-pollutant concentrations measured in the city of Kozani.

Long-range transport and re-circulation of pollutants in the western Mediterranean during the project Regional Cycles of Air Pollution in the West-Central Mediterranean Area

During the warm season (March–September), high ozone concentrations have been reported at the coastal and mountain monitoring stations of the eastern Iberia coast (Millán et al., J. Geophys. Res. 102 (D7) 8811, J. Appl. Meteorol. 4 (2000) 487). The vegetation protection threshold of current Directive 92/72/EEC and the World Health Organisation guideline for the protection of crops and semi-natural vegetation are systematically exceeded during the whole period. The main objective of the present study is to search for the origin of these chronic pollution levels: to search for the reason(s) for such high O 3 concentrations during such a long period. A mesoscale model is used to reproduce the diurnal cycle of winds and stability/layering over the Western Mediterranean Basin (WMB), at a sufficient space/temporal resolution, under a typical recursive synoptic condition during the warm season: data from the flight tracks of the European Project—Regional Cycles of Air Pollution in the West-Central Mediterranean Area—are used to substantiate the model results. Times of residence and the final distribution of pollutants entering the WMB are estimated using single-particle Lagrangian trajectories and a multiple-particle dispersion model. Our results show that the marine boundary layer and the lower troposphere in the region between the Balearic Islands and eastern Iberia are subject to a flow regime that tends to accumulate pollutants within large circulations, covering the entire western basin. We have also shown a diurnal pulsation of the Tramontana/Mistral wind regime, which can transport new pollutants into the area (background concentrations of 50–65 ppb of O 3 of continental European origin) that are added to local emissions and re-circulated within the coastal breezes at eastern Iberia for periods of more than five days. Local emissions and wind configuration contribute to increase the O 3 concentrations up to 100 ppb and even more.

An Observational and Numerical Study of the Nocturnal Sea Breeze. Part II: Chemical Transport

Abstract Chemical transport at the Savannah River Site (SRS) in South Carolina during nocturnal sea-breeze passage is examined using simulations from a three-dimensional mesoscale dynamic model [(RAMS) Regional Atmospheric Modeling System] and a Lagrangian particle dispersion model (LPDM) and supplemental surface measurements of sulfur hexafluoride (SF6) obtained during a 1988 field campaign. Plume dispersion and regional transport were characterized by nights with onshore and offshore synoptic winds. For onshore winds, the sea breeze lifts, redirects, and broadens an initially narrow plume but maintains its general structure. Regional calculations reveal particle translations exceeding 100 km under these conditions. On the other hand, with offshore synoptic winds, frontal passage leads to stronger lifting, turbulence, and vertical shearing that fragments the plume. In addition, complicated recirculation of pollutants is possible and may increase chemical concentrations in areas near the source. Observed ...

Ozone distributions over the los angeles basin: Three-dimensional simulations with the smog model

The UCLA Surface Meteorology and Ozone Generation (SMOG) model has been applied to simulate and analyze the distributions of ozone in the Los Angeles basin on 27 and 28 August 1987, during the Southern California Air Quality Study (SCAQS). SMOG is an integrated air pollution modeling system that includes the coupled effects of meteorology, pollutant sources and dispersion, photochemistry and aerosol microphysics, and radiative processes. High surface ozone concentrations are predicted along the slopes of the surrounding mountain barriers and in the eastern basin, as observed. The pattern of surface ozone concentrations is shown to be influenced by the evolution of oxidants within the temperature inversion that typically blankets the Los Angeles basin. In the past, dense layers of ozone have been observed to be embedded within the temperature inversion, but their origin has remained unexplained. The present model simulations reproduce these and other three-dimensional structures in the ozone distribution, as documented by measurements in the basin. The high concentrations of oxidants aloft are explained through a detailed dynamical/chemical mechanism. High mountains surrounding the Los Angeles basin block the dispersion of ozone and other pollutants and generally contain them within the basin. At the same time, vertical circulations associated with the interaction of the sea-breeze and mountain slope winds inject pollutants into the base of the inversion and create high concentrations of ozone, PAN, nitric acid, organic nitrates and a variety of other pollutants, including aerosols. The contrast between ozone concentrations at the surface and in these elevated layers can be enhanced in the evening by NO emissions, which titrate ozone near the surface. The elevated layers act as a reservoir for aged pollutants, which can be mixed downward on subsequent days to enhance surface concentrations. The recirculation of pollutants in the Los Angeles basin is thus reinforced by the presence of these oxidant layers, and may be responsible for the rapid increase in surface ozone concentrations often seen in the morning, particularly in the eastern basin where emissions of primary pollutants are relatively small. The impact on surface ozone concentrations of recirculated photochemically aged air is estimated to be as high as 8 pphmv in the eastern Los Angeles basin. These simulations represent the first quantitative description of the role of pollutants aloft on surface air quality.

Effect of alternative boundary conditions on predicted ozone control strategy performance: A case study in the Los Angeles area

The purpose of this paper is to illuminate the importance of assumptions made regarding boundary and initial conditions on the predicted performance of regional ozone control strategies. A computationally efficient approach to depicting the response of an air basin to emission controls is developed. The problem of ozone isopleth generation is addressed using a large Eulerian grid-based photochemical airshed model that is distributed over a grid system of 64 different ROG and NO x control combination points that were run simultaneously on a parallel computer. This method is used for the Los Angeles area to examine the effect on predicted ozone concentrations of alternative assumptions about how boundary conditions at the edge of the air basin will change as a result of changed recirculation of pollutants from within the airshed plus emission decreases upwind. We show that an accurate forecast of the effect of future emission control programs on pollutant inflows across the boundaries of the Los Angeles modeling region is absolutely critical to selection of a successful ozone control strategy for the Los Angeles area.

Possible accumulation and recirculation of pollutants in the atmosphere of the Highveld

Possible accumulation and recirculation of pollutants in the atmosphere of the Highveld

The effects of mesoscale circulation on the dispersion of pollutants (SO 2) in the eastern Mediterranean, southern coastal plain of Israel

A three-dimensional numerical mesoscale air quality model is applied to study the effect of pollutant recirculation in the eastern Mediterranean, southern coastal plain of Israel. The model is based on the integration of two submodels: a mesoscale submodel and a Lagrangian dispersion submodel. The model is validated using air quality data measured during a severe pollution event in the city of Ashdod. When the recirculated portion of the pollution was separated from that directly contributed by the sources, it was found to constitute about 50% of the total concentration measured.

Analysis of Mesoscale Airflow Patterns in the South-Central Coast Air Basin during the SCCCAMP 1985 Intensive Measurement Periods

An analysis of the mesoscale airflow patterns in the south-central coast air basin (SCCAB) was performed using data collected during the 1985 South-Central Coast Cooperative Aerometric Monitoring Program (SCCCAMP). Airflow within the SCCAB is strongly influenced by the diurnal sea-breeze/land-breeze cycle and by slope flows that develop along the steep terrain. Mesoscale airflow features observed during the four intensive monitoring periods include eddies along the coast and over the Santa Barbara Channel. An analysis of the transport patterns indicated that both recirculation of pollutants within the SCCAB and transport of pollutants from the south coast air basin (SOCAB) contributed to the observed high ozone concentrations on the intensive monitoring days.

Characteristics of Ozone Episodes during SCCCAMP 1985

Abstract Extensive meteorological and air chemistry measurements were obtained along the Ventura and Santa Barbara county coastal areas in California during four 2–3 day case studies conducted during the September–October 1985 South-Central Coast Cooperative Aerometric Monitoring Program (SCCCAMP 1985). An overview of the characteristics of ozone episodes during these four case studies is given, showing that the episodes are associated with warm, high pressure systems with light winds. In the absence of easterly winds, the observed ozone in the region is primarily due to local sources. At other times, easterly wind components transport ozone and its precursors from large source regions to the east (i.e., Los Angeles County). This transport sometimes occurs in inland valleys at elevations up to 600 m, and sometimes occurs over the ocean near the surface. Local sea breezes, mesoscale eddies, and terrain-generated winds often cause complex flow patterns and recirculation of pollutants.

Overview of Results of Analysis of Data from the South-Central Coast Cooperative Aerometric Monitoring Program (SCCCAMP 1985)

The subject of this paper is an overview of the data analysis collected during the comprehensive five-week South-Central Coast Cooperative Air Monitoring Program (SCCCAMP 1985) in California during September and October 1985. The various data analyses have been designed to develop a better understanding of the atmospheric processes that cause elevated ozone concentrations in the region, which includes Ventura and Santa Barbara counties. The data analyses lead to the conclusion that the ozone episodes observed during the field study are typical of those occurring during the past several years and are most strongly correlated with clear skies, high temperatures (i.e., warm high pressure), and with pressure gradients that would imply an easterly component to the wind flow. These episodes are also marked by mixing depths of 100 m or less over the water and by low mixing depths (i.e., a few hundred meters) over the coastal plains. While it is clear that much of the local ozone is caused by local sources, it is also evident that during many ozone episodes, ozone and its precursors are advected into the region from sources to the east, in the vicinity of Los Angeles. Observed ozone and wind patterns suggest that this advection sometimes takes place at elevations of a few hundred meters through inland valleys and along the coast, and sometimes it takes place in a shallow layer near the surface over the coastal ocean. Because of the presence of time-varying sea breezes and mesoscale eddies, it is possible for recirculation of pollutants to occur, as verified by tracer experiments conducted during the field study.