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Differential Optical Absorption Spectroscopy를 이용한 대기오염 측정 및 분석

. Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements of sulfur dioxide (SO2) have been performed at the Xianghe station (39.8° N, 117.0° E) located at ~ 50 km southeast of Beijing from March 2010 to February 2013. Tropospheric SO2 vertical profiles and corresponding vertical column densities (VCDs), retrieved by applying the optimal estimation method to the MAX-DOAS observations, have been used to study the seasonal and diurnal cycles of SO2, in combination with correlative measurements from in situ instruments, as well as meteorological data. A marked seasonality was observed in both SO2 VCD and surface concentration, with a maximum in winter (February) and a minimum in summer (July). This can be explained by the larger emissions in winter due to the domestic heating and, in case of surface concentration, by more favorable meteorological conditions for the accumulation of SO2 close to the ground during this period. Wind speed and direction are also found to be two key factors in controlling the level of the SO2-related pollution at Xianghe. In the case of east or southwest wind, the SO2 concentration does not change significantly with the wind speed, since the city of Tangshan and heavy polluting industries are located to the east and southwest of the station, respectively. In contrast, when wind comes from other directions, the stronger the wind, the less SO2 is observed due to a more effective dispersion. Regarding the diurnal cycle, the SO2 amount is larger in the early morning and late evening and lower at noon, in line with the diurnal variation of pollutant emissions and atmospheric stability. A strong correlation with correlation coefficients between 0.6 and 0.9 is also found between SO2 and aerosols in winter, suggesting that anthropogenic SO2, through the formation of sulfate aerosols, contributes significantly to the total aerosol content during this season. The observed diurnal cycles of MAX-DOAS SO2 surface concentration are also in very good agreement (correlation coefficient close to 0.9) with those from collocated in situ data, indicating the good reliability and robustness of our retrieval.

/pdf/evaluation-of-tropospheric-so-2-retrieved-from-max-doas-1lrbdwq03u.pdf

Evaluation of tropospheric SO 2 retrieved from MAX-DOAS measurements in Xianghe, China

This study presents the assessment of nitrogen dioxide (NO2) pollution within the twin cities of Islamabad and Rawalpindi by using car MAX-DOAS (Multi Axis-Differential Optical Absorption Spectroscopy) instrument during two different scenarios of with and without the availability of CNG (compressed natural gas) fuel. Information perceived from this study can be used to get an idea about recent air quality conditions of twin cities and its repercussions on ecological and human health. International air quality monitoring field campaigns were conducted during November 2012 and December 2013. Results showed different concentrations of NO2 (68.2, 74.25 and 93.65 ppb) at various locations of Islamabad and Rawalpindi cities, exceeded the Pak-NEQS levels of 42.5 ppb. High NO2 concentrations can be attributed to emissions from an oil refinery, traffic congestion and solid waste dump site along IJP road, and due to non-availability of CNG during December 2013. Results compared with OMI satellite observations exhibited that NO2 columns from OMI observations are largely underestimated.

/pdf/temporal-assessment-of-no2-pollution-levels-in-urban-centers-3dg6ajgk0l.pdf

Temporal Assessment of NO2 Pollution Levels in Urban Centers of Pakistan by Employing Ground-Based and Satellite Observations

Scanning and mobile multi-axis DOAS measurements of SO2 and NO2 emissions from an electric power plant in Montevideo, Uruguay

 Accurate gas velocity measurements in emission plumes are highly desirable for various atmospheric remote sensing applications The imaging technique of UV SO2 cameras is commonly used to monitor SO2 emissions from volcanoes and anthropogenic sources (eg power plants, ships) The camera systems capture the emission plumes at high spatial and temporal resolution This allows the gas velocities in the plume to be retrieved directly from the images The latter can be measured at a pixel level using optical flow (OF) algorithms This is particularly advantageous under turbulent plume conditions However, OF algorithms intrinsically rely on contrast in the images and often fail to detect motion in low-contrast image areas We present a new method to identify ill-constrained OF motion vectors and replace them using the local average velocity vector The latter is derived based on histograms of the retrieved OF motion fields The new method is applied to two example data sets recorded at Mt Etna (Italy) and Guallatiri (Chile) We show that in many cases, the uncorrected OF yields significantly underestimated SO2 emission rates We further show that our proposed correction can account for this and that it significantly improves the reliability of optical-flow-based gas velocity retrievals In the case of Mt Etna, the SO2 emissions of the north-eastern crater are investigated The corrected SO2 emission rates range between 48 and 107 kg s−1 (average of 71  ±  13 kg s−1) and are in good agreement with previously reported values For the Guallatiri data, the emissions of the central crater and a fumarolic field are investigated The retrieved SO2 emission rates are between 05 and 29 kg s−1 (average of 13  ±  05 kg s−1) and provide the first report of SO2 emissions from this remotely located and inaccessible volcano

/pdf/improved-optical-flow-velocity-analysis-in-so-2-camera-3jzaoaunq6.pdf

Improved optical flow velocity analysis in SO 2 camera images of volcanic plumes - implications for emission-rate retrievals investigated at Mt Etna, Italy and Guallatiri, Chile

We performed measurements of SO2 emissions with a high UV sensitive dual-camera optical system. Generally, in order to retrieve the two-dimensional SO2 emission rates of a source, e.g., the slant column density of a plume emitted by a stack, one needs to acquire four images with UV cameras: two images including the emitting stack at wavelengths with high and negligible absorption features (λon/off), and two additional images of the background intensity behind the plume, at the same wavelengths as before. However, the true background intensity behind a plume is impossible to obtain from a remote measurement site at rest, and thus, one needs to find a way to approximate the background intensity. Some authors have presented methods to estimate the background behind the plume from two emission images. However, those works are restricted to dealing with clear sky, or almost homogeneously illuminated days. The purpose of this work is to present a new approach using background images constructed from emission images by an automatic plume segmentation and interpolation procedure, in order to estimate the light intensity behind the plume. We compare the performance of the proposed approach with the four images method, which uses, as background, sky images acquired at a different viewing direction. The first step of the proposed approach involves the segmentation of the SO2 plume from the background. In clear sky days, we found similar results from both methods. However, when the illumination of the sky is non homogeneous, e.g., due to lateral sun illumination or clouds, there are appreciable differences between the results obtained by both methods. We present results obtained in a series of measurements of SO2 emissions performed on a cloudy day from a stack of an oil refinery in Montevideo City, Uruguay. The results obtained with the UV cameras were compared with scanning DOAS measurements, yielding a good agreement.

Plume Segmentation from UV Camera Images for SO2 Emission Rate Quantification on Cloud Days

We present preliminary results of ground based measurements of SO2 and NO2 emissions from "La Teja" oil refinery located in the northern part of Montevideo Bay. Our study is part of a long term effort to localize and monitor relevant emission sources in the city area of Montevideo. These measurements were performed with a Miniature Multi AXis Differential Optical Absorption Spectrometry (MiniMAX-DOAS) instrument, which is basically a temperature controlled medium-resolution spectrometer (~ 0.5 nm) equipped with a small telescope and a stepper motor allowing automatic scans in one dimension. We present a discussion about the evolution and transformation of both above species in the atmosphere. Our observation site was approximately 1.9 km away from the oil refinery and we were able to perform vertical and horizontal scans of the plume emitted (during our measurements) almost horizontally from its stacks. The maximum value of the SO2 slant column density (SCD) was found to be ~ 4×1017 molec cm−2 directly over the oil refinery, decreasing as the plume disperses. In contrast, the NO2 SCD peaks at ~ 1×1016 molec cm−2 directly over the source and increases continuously as the plume disperses. The SO2 flux measured immediately downwind of the refinery was found to be about 1200 kg h−1 (±40% uncertainty).

http://iopscience.iop.org/article/10.1088/1742-6596/274/1/012083/pdf

Ground based measurements of SO2 and NO2 emissions from the oil refinery "la Teja" in Montevideo city

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017EA000341

Comparison Between Regularized Optimization Algorithms for Tomographic Reconstruction of Plume Cross Sections in the Atmosphere

. In the present work we deal with emissions originating from combustion processes containing SO2, NO and NO2, emitted into the atmosphere by a localized source. We present a method for measuring the NO2-formation rate (due to conversion of NO to NO2) from measurements of SO2- and NO2-slant column densities across different plume sections, under the (usually justified) assumption that the SO2-flux is constant. The advantages of the proposed method are that the measurements can be performed from an arbitrary location, without explicit reference to the wind speed and direction in the plume. We present results of ground based DOAS-measurements of SO2 and NOx emissions from an oil refinery located in the northern part of Montevideo Bay and give recommendations for future applications of the method.

/pdf/doas-measurement-of-the-no2-formation-rate-from-nox-53def629a4.pdf

Nicolás Casaballe

Papers

Scanning and mobile multi-axis DOAS measurements of SO2 and NO2 emissions from an electric power plant in Montevideo, Uruguay

Plume Segmentation from UV Camera Images for SO2 Emission Rate Quantification on Cloud Days

Ground based measurements of SO2 and NO2 emissions from the oil refinery "la Teja" in Montevideo city

Comparison Between Regularized Optimization Algorithms for Tomographic Reconstruction of Plume Cross Sections in the Atmosphere

DOAS-measurement of the NO2 formation rate from NOx emissions into the atmosphere