Effective Emission Heights Research Articles

Structure, variability, and origin of the low-latitude nightglow continuum between 300 and 1800 nm: evidence for HO2 emission in the near-infrared

Abstract. The Earth's mesopause region between about 75 and 105 km is characterised by chemiluminescent emission from various lines of different molecules and atoms. This emission was and is important for the study of the chemistry and dynamics in this altitude region at nighttime. However, our understanding is still very limited with respect to molecular emissions with low intensities and high line densities that are challenging to resolve. Based on 10 years of data from the astronomical X-shooter echelle spectrograph at Cerro Paranal in Chile, we have characterised in detail this nightglow (pseudo-)continuum in the wavelength range from 300 to 1800 nm. We studied the spectral features, derived continuum components with similar variability, calculated climatologies, studied the response to solar activity, and even estimated the effective emission heights. The results indicate that the nightglow continuum at Cerro Paranal essentially consists of only two components, which exhibit very different properties. The main structures of these components peak at 595 and 1510 nm. While the former was previously identified as the main peak of the FeO “orange arc” bands, the latter is a new discovery. Laboratory data and theory indicate that this feature and other structures between about 800 and at least 1800 nm are caused by emission from the low-lying A′′ and A′ states of HO2. In order to test this assumption, we performed runs with the Whole Atmosphere Community Climate Model (WACCM) with modified chemistry and found that the total intensity, layer profile, and variability indeed support this interpretation, where the excited HO2 radicals are mostly produced from the termolecular recombination of H and O2. The WACCM results for the continuum component that dominates at visual wavelengths show good agreement for FeO from the reaction of Fe and O3. However, the simulated total emission appears to be too low, which would require additional mechanisms where the variability is dominated by O3. A possible (but nevertheless insufficient) process could be the production of excited OFeOH by the reaction of FeOH and O3.

Effective Emission Heights of Various OH Lines From X‐Shooter and SABER Observations of a Passing Quasi‐2‐Day Wave

AbstractChemiluminescent radiation of the vibrationally and rotationally excited hydroxyl (OH) radical, which dominates the nighttime near‐infrared emission of the Earth's atmosphere in wide wavelength regions, is an important tracer of the chemical and dynamical state of the mesopause region between 80 and 100 km. As radiative lifetimes and rate coefficients for collision‐related transitions depend on the OH energy level, line‐dependent emission profiles are expected. However, except for some height differences for whole bands mostly revealed by satellite‐based measurements, there is a lack of data for individual lines. We succeeded in deriving effective emission heights for 298 OH lines thanks to the joint observation of a strong quasi‐2‐day wave (Q2DW) in eight nights in 2017 with the medium‐resolution spectrograph X‐shooter at the Very Large Telescope at Cerro Paranal in Chile and the limb‐sounding SABER radiometer on the TIMED satellite. Our fitting procedure revealed the most convincing results for a single wave with a period of about 44 hr and a vertical wavelength of about 32 km. The line‐dependent as well as altitude‐resolved phases of the Q2DW then resulted in effective heights which differ by up to 8 km and tend to increase with increasing vibrational and rotation excitation. The measured dependence of emission heights and wave amplitudes (which were strongest after midnight) on the line parameters implies the presence of a cold thermalized and a hot non‐thermalized population for each vibrational level.

Air Pollution and Economic Impact from Ships Operating in the Port of Varna

The present work develops a multidisciplinary approach for evaluating the air pollution and economic impact from ships operating in the port of Varna. The work collects and analyses automatic identification system (AIS) data of the arriving and queuing dry cargo ships in the seaport of Varna in identifying the statistical descriptors of the length of the ships, gross tonnage (GT), and ship engine power. The queueing theory (QT) is employed to analyse the ship operations in a single queue and is processed by three parallel terminals, satisfying the port regulations. The Gaussian dispersion model (GDM) is adopted to predict the pollution concentration from ships arriving at the seaport, queuing, approaching, waiting, processing at the berth, and departing. The gas emission is estimated as a function of the ship movement trajectory, and the time duration at any stage is defined by QT for the most critical surrounding areas, considering the wind speed, as well as horizontal and vertical dispersion as a function of the location of the ship, accounting for the effective emission height, weather conditions, and speed. To mitigate the potential impact on health, the gas emissions of oxides of nitrogen (NOx), sulphur dioxide (SO2), and air-borne particles (PM10) generated by ships during the queuing and port operation are evaluated. Potential cleaning measures for any ship are implemented to satisfy the maximum allowable concentrations (MAC) in surrounding areas. The implemented ship pollution cleaning measures and overall ship and terminal operating costs are minimised to identify the most efficient berth operation. The developed approach is flexible and can be used for any particular conditions for ships operating in ports.

Stochastic Air Quality Dispersion Model for Defining Queuing Ships Seaport Location

This work develops a stochastic air quality dispersion to predict the pollution concentration originating from ships queuing in a seaport. The Gaussian dispersion model for five ships operating in the Black Sea queuing in the front of the port of Varna as sources of gas emission of NOx, SOx and PM10 is used to define the air pollution concentration at receptors (crowded areas of the port and other reference points) and consequently the distance to the seaport queuing location. Uncertainties, which are inherent in the input data and mathematical model, are accounted for to estimate the propagating uncertainties of the emission concentration at the receptors accounting for the wind speed, horizontal and vertical dispersion parameters as a function of the geographical location of the emission sources (ships), effective emission height and weather conditions. The estimated uncertainties of the air quality prediction are of significant importance for the decision-making on the regulatory purposes, and the probability of exceeding the threshold limits needs to be quantified. The most expected value and the probability of exceeding the acceptable limits of pollution concentration are defined by employing the first-order reliability method. The target reliability level is defined as the failure cause and mode used for identifying the safety calibration factors that may be employed for defining the most suitable location of the ship queuing seaport. Several conclusions about the applicability of the developed stochastic model and its use for regulatory purposes are also provided.

Dependence of Climate Sensitivity on the Given Distribution of Relative Humidity

AbstractWe study how the vertical distribution of relative humidity (RH) affects climate sensitivity, even if it remains unchanged with warming. Using a radiative‐convective equilibrium model, we show that the climate sensitivity depends on the shape of a fixed vertical distribution of humidity, tending to be higher for atmospheres with higher humidity. We interpret these effects in terms of the effective emission height of water vapor. Differences in the vertical distribution of RH are shown to explain a large part of the 10%–30% differences in clear‐sky sensitivity seen in climate and storm‐resolving models. The results imply that convective aggregation reduces climate sensitivity, even when the degree of aggregation does not change with warming. Combining our findings with RH trends in reanalysis data shows a tendency toward Earth becoming more sensitive to forcing over time. These trends and their height variation merit further study.

Ambient air quality data reported at Sasol Secunda monitoring stations during COVID-19 lockdown – Mpumalanga, South Africa

Various local and international research has been published on the effects of COVID-19 lockdown on ambient air quality. In most cases, a reduction in ambient NOx and PM concentrations have been observed with varying changes in ambient SO2 levels. Secunda, located in the Highveld Priority Area in Mpumalanga, South Africa is known for its large industrial facilities utilising coal as primary feedstock. The towns of Secunda and eMbalenhle provide the majority of the workforce to Sasol and has therefore been the focus of this study. The ambient air quality in the Secunda region was assessed due to the changes in human behaviour during lockdown, familiarity with the Sasol facility and the strategic locations of ambient air quality stations.Results show a clear decrease in ambient CO, NO2 and PM concentrations, especially during the first two weeks of lockdown. Only subtle changes were observed for ambient H2S and SO2 pollutant concentrations at the ambient monitoring stations. An increasing trend in all ambient species was observed towards the end and post lockdown, in contrast to declining ambient temperatures with the onset of winter. This is also contrary to the reduction in emissions from the factory that conducted annual maintenance in the month following lockdown (phase shutdown). This article concludes that human behaviour has a material local ambient impact on CO, NO2 and PM pollutant species, while H2S concentration profiles are more directly related to the industrial complex’s levels of activity. Ambient SO2 trends did not show a similar correlation with the facility’s activities (as H2S), but a stronger correlation was observed with the diverse local and regional sources in close proximity to Secunda and eMbalenhle. The influence of better dispersion especially on a local scale, brought about by more effective emission heights, is considered material. Moreover, meteorological factors, on local air quality, has been shown to be a material contributor to observed ambient air quality levels in the study domain

OH level populations and accuracies of Einstein-<i>A</i> coefficients from hundreds of measured lines

Abstract. OH airglow is an important nocturnal emission of the Earth's mesopause region. As it is chemiluminescent radiation in a thin medium, the population distribution over the various roto-vibrational OH energy levels of the electronic ground state is not in local thermodynamic equilibrium (LTE). In order to better understand these non-LTE effects, we studied hundreds of OH lines in a high-quality mean spectrum based on observations with the high-resolution Ultraviolet and Visual Echelle Spectrograph at Cerro Paranal in Chile. Our derived populations cover vibrational levels between v=3 and 9, rotational levels up to N=24, and individual Λ-doublet components when resolved. As the reliability of these results critically depends on the Einstein-A coefficients used, we tested six different sets and found clear systematic errors in all of them, especially for Q-branch lines and individual Λ-doublet components. In order to minimise the deviations in the populations for the same upper level, we used the most promising coefficients from Brooke et al. (2016) and further improved them with an empirical correction approach. The resulting rotational level populations show a clear bimodality for each v, which is characterised by a probably fully thermalised cold component and a hot population where the rotational temperature increases between v=9 and 4 from about 700 to about 7000 K, and the corresponding contribution to the total population at the lowest N decreases by an order of magnitude. The presence of the hot populations causes non-LTE contributions to rotational temperatures at low N, which can be estimated quite robustly based on the two-temperature model. The bimodality is also clearly indicated by the dependence of the populations on changes in the effective emission height of the OH emission layer. The degree of thermalisation decreases with increasing layer height due to a higher fraction of the hot component. Our high-quality population data are promising with respect to a better understanding of the OH thermalisation process.

The effect of heat recovery on near-source plume dispersion of a simple cycle gas turbine

The waste heat recovery (HR) systems are employed to increase the overall thermal efficiency of electric generation units (EGUs). Although the emission factors (in terms of gram of pollutants per unit of thermal energy consumed or electric energy generated) generally decreases after installing HR systems, the emission rates in terms of grams of pollutants per unit of time remain unchanged. However, HR systems reduce stack exit temperature, resulting in lower effective emission heights, which lead to higher near-source ground level concentrations (GLCs) of air pollutants. In order to comprehensively evaluate the near-source air quality impact from deploying HR systems, we proposed a new modeling framework by integrating a computationally efficient Gaussian-based dispersion model (AERMOD) and a (relatively) more accurate computational fluid dynamics (CFD) model. As a demonstration of the proposed framework, we investigated the HR impact on NOx concentrations near a simple cycle gas turbine located in Brentwood, NY. Specifically, we applied the AERMOD modeling system to screen the hourly GLCs over five years, and highest values (and the corresponding hours) were shown to cluster into two main meteorological conditions: the stable atmospheric boundary layer with relatively high wind speed (Stable, HW) and the unstable atmospheric boundary layer with relatively low wind speed (Unstable, LW). These two conditions were further simulated using a CFD model that have been extensively evaluated previously for detailed analysis. By setting different stack exit temperatures, the near-source air quality impact of different waste heat conversion rates was evaluated. We introduced a concept called the heat recovery amplified factor (HRAF), defined as the ratio between the maximum GLC with HR system and that without HR system, as an indicator of HR impact. HRAF was shown to be much more sensitive to temperature in the Unstable, LW condition than in the Stable, HW condition. Although the results were limited to a specific simple cycle gas turbine, the proposed modeling framework and HRAF can be used for evaluating the HR systems impact for other emission sources.

Implementation of plume rise and its impacts on emissions and air quality modelling

This work analyses the impact of implementing hourly plume rise calculations over Spain in terms of: i) vertical emission allocations and ii) modelled air quality concentrations. Two air quality simulations (4 km × 4 km, 1 h) were performed for February and June 2009, using the CALIOPE-AQFS system (WRF-ARW/HERMESv2.0/CMAQ/BSC-DREAM8b) differing only by the vertical allocation of point source emissions: i) using fixed vertical profiles based on the stack height of each facility and ii) using an hourly bottom-up calculations of effective emission heights. When using plume rise calculations, emissions are generally allocated to lower altitudes than when using the fixed vertical profiles, showing significant differences depending on source sector and air pollutant (up to 75% between estimated average effective emission heights). In terms of air quality, it is shown that hourly plume rise calculations lead to improved simulation of industrial SO2 concentrations, thus increasing modelled concentrations (1.4 μg m−3 increase in February, 1.5 μg m−3 increase in June) and reducing the model biases for both months (31.1% in February, 73.7% in June). The increase of SO2 concentrations leads to an increase of SO4−2 surface levels that varies according to the season and location (4.3% in February and 0.4% in June, on average). On the other hand, the impact on NO2 and PM10 concentrations is less significant, leading to average changes of a few μg·m3 at most (0.4 μg m−3 for NO2 and 0.2 μg m−3 for PM10). In order to maximize the precision of plume rise calculations, the use of stack parameters based on real-world data is mandatory.

Impact of the vertical emission profiles on background gas-phase pollution simulated from the EMEP emissions over Europe

Abstract. Five one-year air quality simulations over a domain covering Europe have been performed using the CHIMERE chemistry transport model and the EMEP emission dataset for Europe. These five simulations differ only by the representation of the effective emission heights for anthropogenic emissions: one has been run using the EMEP standard recommendations, three others with vertical injection profiles derived from the EMEP recommendations but multiplying the injection height by 0.75, 0.50 and 0.25, respectively, while the last one uses vertical profiles derived from the recent literature. It is shown that using injection heights lower than the EMEP recommendations leads to significantly improved simulation of background SO2, NO2 and O3 concentrations when compared to the Airbase station measurements.

Vertical emission profiles for Europe based on plume rise calculations

The vertical allocation of emissions has a major impact on results of Chemistry Transport Models. However, in Europe it is still common to use fixed vertical profiles based on rough estimates to determine the emission height of point sources. This publication introduces a set of new vertical profiles for the use in chemistry transport modeling that were created from hourly gridded emissions calculated by the SMOKE for Europe emission model. SMOKE uses plume rise calculations to determine effective emission heights. Out of more than 40 000 different vertical emission profiles 73 have been chosen by means of hierarchical cluster analysis. These profiles show large differences to those currently used in many emission models. Emissions from combustion processes are released in much lower altitudes while those from production processes are allocated to higher altitudes. The profiles have a high temporal and spatial variability which is not represented by currently used profiles.

Effective pollutant emission heights for atmospheric transport modelling based on real-world information

Emission data needed as input for the operation of atmospheric models should not only be spatially and temporally resolved. Another important feature is the effective emission height which significantly influences modelled concentration values. Unfortunately this information, which is especially relevant for large point sources, is usually not available and simple assumptions are often used in atmospheric models. As a contribution to improve knowledge on emission heights this paper provides typical default values for the driving parameters stack height and flue gas temperature, velocity and flow rate for different industrial sources. The results were derived from an analysis of the probably most comprehensive database of real-world stack information existing in Europe based on German industrial data. A bottom-up calculation of effective emission heights applying equations used for Gaussian dispersion models shows significant differences depending on source and air pollutant and compared to approaches currently used for atmospheric transport modelling.

Satellite-based detection of volcanic sulphur dioxide from recent eruptions in Central and South America

Abstract. Volcanic eruptions can emit large amounts of rock fragments and fine particles (ash) into the atmosphere, as well as several gases, including sulphur dioxide (SO2). These ejecta and emissions are a major natural hazard, not only to the local population, but also to the infrastructure in the vicinity of volcanoes and to aviation. Here, we describe a methodology to retrieve quantitative information about volcanic SO2 plumes from satellite-borne measurements in the UV/Visible spectral range. The combination of a satellite-based SO2 detection scheme and a state-of-the-art 3D trajectory model enables us to confirm the volcanic origin of trace gas signals and to estimate the plume height and the effective emission height. This is demonstrated by case-studies for four selected volcanic eruptions in South and Central America, using the GOME, SCIAMACHY and GOME-2 instruments.

Bayer to cut further jobs

The waste heat recovery (HR) systems are employed to increase the overall thermal efficiency of electric generation units (EGUs). Although the emission factors (in terms of gram of pollutants per unit of thermal energy consumed or electric energy generated) generally decreases after installing HR systems, the emission rates in terms of grams of pollutants per unit of time remain unchanged. However, HR systems reduce stack exit temperature, resulting in lower effective emission heights, which lead to higher near-source ground level concentrations (GLCs) of air pollutants. In order to comprehensively evaluate the near-source air quality impact from deploying HR systems, we proposed a new modeling framework by integrating a computationally efficient Gaussian-based dispersion model (AERMOD) and a (relatively) more accurate computational fluid dynamics (CFD) model. As a demonstration of the proposed framework, we investigated the HR impact on NOx concentrations near a simple cycle gas turbine located in Brentwood, NY. Specifically, we applied the AERMOD modeling system to screen the hourly GLCs over five years, and highest values (and the corresponding hours) were shown to cluster into two main meteorological conditions: the stable atmospheric boundary layer with relatively high wind speed (Stable, HW) and the unstable atmospheric boundary layer with relatively low wind speed (Unstable, LW). These two conditions were further simulated using a CFD model that have been extensively evaluated previously for detailed analysis. By setting different stack exit temperatures, the near-source air quality impact of different waste heat conversion rates was evaluated. We introduced a concept called the heat recovery amplified factor (HRAF), defined as the ratio between the maximum GLC with HR system and that without HR system, as an indicator of HR impact. HRAF was shown to be much more sensitive to temperature in the Unstable, LW condition than in the Stable, HW condition. Although the results were limited to a specific simple cycle gas turbine, the proposed modeling framework and HRAF can be used for evaluating the HR systems impact for other emission sources.

An operational puff dispersion model

An operational puff dispersion model is described, which is adapted from the work of Van Egmond and Kesseboom ( Atmospheric Environment 17, 265–274, 1983). It is intended for operational use at KNMI and RIVM in case of an accidental release of toxic or radioactive gases or particles into the atmosphere. The area covered by the model is restricted by the meteorological input that is available; the operational version will cover Europe. The main processes accounted for by the model are relative diffusion by wind shear and turbulence, advection as a function of space and time, the diurnal cycle of boundary layer height and stability, dry and wet deposition and linear chemical transformation or radioactive decay. Input fields for the model are horizontal wind (every 3 or 6 h; on two or three levels), precipitation data (every 3 h; optional) and height of the boundary layer (or mixed layer; every 3 h; optional). The meteorological data used may be either analyses or prognostic fields. The source is defined by an effective emission height and a source strength as a function of time. The model calculates fields of concentrations near the surface and dry and wet depositions as a function of time. The model is tested on the cesium-137 and iodine-131 dispersion over Europe during the Chernobyl episode (April and May 1986). A 10-day period is simulated and results are compared with measurements. Arrival times of the material are simulated very well, in most cases within 6 h accuracy. The observed air concentrations and model outcome show reasonable agreement.

Estimation of source-receptor matrices for deposition of NOx-N

The contributions of the anthropogenic sources of NOx from various combinations of contiguous U.S. states or Canadian provinces to integrated deposition across selected states or provinces are estimated with the Advanced Statistical Trajectory Regional Air Pollution (ASTRAP) model. The model assumes linearity between emissions and deposition, and uses the same parameterization methods, although with different rates, as in simulations of transport and deposition of SOX. Vertical distributions of emissions for the two classes of pollutants are substantially different in the gridded inventories used in simulations, with a weighted mean effective emission height of 160 m for NOX and 310 m for SOX. This might be expected to lead to an effective transport distance before deposition shorter for NOX than for SOX. However, the calculated fraction of NOX emissions deposited within the contiguous United States and Canada south of 60 deg N (57%) is not greatly different from the fraction calculated for SOX emissions (54%). This suggests that there may be compensating factors in the horizontal distribution of NOX emissions, and in the lower dry deposition velocities for NO/NO2 than for SO2 in ASTRAP.

A Method for Propagating Measurement Uncertainties through Dispersion Models

Results from dispersion models which are routinely used for regulatory purposes do not reflect the uncertainties which are inherent in the input data. To remedy this, a formula for propagating measurement uncertainties of emission rate, wind speed, wind direction, horizontal dispersion parameter, vertical dispersion parameter, effective emission height, and mixing depth is derived for EPA's Industrial Source Complex Short Term (ISCST) Gaussian dispersion model for the simple case of a single stack-type source and nonbuoyant plume. Values for the uncertainties of the input variables are chosen and used to calculate ambient concentration uncertainties. These calculated uncertainties are compared with the standard deviation of ambient concentrations calculated from 2500 input data sets for each of four stability classes and three downwind distances, which were randomly altered to simulate the effects of measurement uncertainty. The calculated uncertainties do not differ significantly from the standard deviations of the randomized calculations for input data uncertainties as high as 30 percent and Stability Classes A-C. The calculated uncertainties overestimate the actual uncertainty of model calculations for input data uncertainties greater than 20 percent for Stability Class D.

Frequency of potential contributions by major sources to ground level concentrations of so 2 in the forth valley, scotland: an application of acoustic sounding

Inversion statistics based on acoustic sounding or SODAR returns for a 12-month period during 1976–1977 were used in the estimation of the frequencies of potential contribution to ground-level SO 2 concentrations by major sources in the Forth Valley, Scotland. The sources were categorized by stack height and assumptions made regarding both effective emission heights and abilities to penetrate elevated and ground-based inversions. The results are presented for the whole summer and winter 6-month periods and for a selection of high-pollution periods during each of these seasons. Comparison between distributions of source contributions and SODAR categories by hour of day gives an indication of the potentially more significant times of contribution during the 24-h period.