In this study, we present a regional insight into characteristics and formation process of the widespread extreme haze pollution in northern China during January of 2013 using integrated satellite ...observations and ground measurements. Different from common regional pollution, dense haze clouds during the most polluted period not only wandered over northern China for more than one week, but also exhibited large spatial variations with some abrupt peak values in Beijing. High UV Aerosol Index (UVAI) values >2.5 indicate prevalent absorbing aerosols in upper part of the haze clouds. CALIPSO vertical detection shows that the haze layers were more than 3 km thick, with strong extinction within 1 km near surface and elevated dust layers above. Top of the more than 2 km thick dust plumes can reach 5 km, having a substantial contribution to the haze clouds. Movement of high aerosol loading regions with aerosol optical depth (AOD) exceeding 2.0 shows a notable superposition of different pollution processes within boundary layer, which largely enhanced the haze pollution. Peak value of PM10 in industrial cities of Hebei was around 1000 μg/m3, almost twice of that in usual pollution. Subsequent peak values of PM10 from south to north confirm the intense regional transport, which could be the main cause of sudden record-breaking particle concentration in Beijing. Anomalous weather conditions facilitated the unusual heavy pollution became extremely severe. Our results indicate close connections between variation of atmospheric circulation and the regional heavy pollution over northern China.
•Regional insight into widespread extreme haze pollution over eastern China.•Abrupt peak values in Beijing could be caused by regional transport.•The extreme pollution was a special event caused by anomalous weather condition.•Close connections exist between regional air pollution and atmospheric circulation.
Pansharpening integrates the high spectral content of multispectral (MS) images and the fine spatial information of the corresponding panchromatic (PAN) images to produce a high spectral-spatial ...resolution image. Traditional pansharpening methods compensate for the spatial lack of the MS image using the PAN image details, which easily causes spectral distortion. To achieve spectral fidelity, a spectral preservation model based on spectral contribution and dempendence with detail injection for pansharpening is proposed. In the proposed model, first, an efficacy coefficient (CE) based on the spatial difference between the MS and PAN images is designed to suppress the impact of the detail injection on the spectra. Second, the spectral contribution and dependence (SCD) between the MS bands and pixels are considered to strengthen the internal adaptation of the spectra. Finally, a spectrally preserved model based on CE and SCD is designed to force the fused image fidelity in spectra when the MS image is pansharpened with the details of the PAN image. Experimental results show that the proposed model is effective.
A strong precipitation event caused by the southwest vortex（SWV）, which affected Sichuan Province and Chongqing municipality in Southwest China on 10–14 July 2012, is investigated. The SWV is ...examined using satellite observations from AIRS（Atmospheric Infrared Sounder）, in situ measurements from the SWV intensive observation campaign, and MICAPS（Marine Interactive Computer-Aided Provisioning System） data. Analysis of this precipitation process revealed that：（1）heavy rain occurred during the development phase, and cloud water content increased significantly after the dissipation of the SWV;（2） the area with low outgoing longwave radiation values from AIRS correlated well with the SWV;（3） variation of the temperature of brightness blackbody（TBB） from AIRS reflected the evolution of the SWV, and the values of TBB reduced significantly during the SWV＇s development; and（4） strong temperature and water vapor inversions were noted during the development of the SWV. The moisture profile displayed large vertical variation during the SWV＇s puissant phase,with the moisture inversion occurring at low levels. The moisture content during the receding phase was significantly reduced compared with that during the developing and puissant phases. The vertical flux of vapor divergence explained the variation of the moisture profile. These results also indicate the potential for using AIRS products in studying severe weather over the Tibetan Plateau and its surroundings, where in situ measurements are sparse.
This paper presents the characterization and validation of retrievals of atmospheric methane (CH4) vertical profiles by the Atmospheric Infrared Sounder (AIRS) on the EOS/Aqua platform. AIRS channels ...near 7.6 μm are used for CH4 retrieval, and they are most sensitive to the middle to upper troposphere, i.e., about 200–300 hPa in the tropics and 400–500 hPa in the polar region. The atmospheric temperature‐humidity profiles, surface skin temperature, and emissivity required to derive CH4 are obtained from retrievals using separate AIRS channels and the Advanced Microwave Sounding Unit (AMSU). Comparison of AIRS retrieved profiles with some in situ aircraft CH4 profiles implied that the forward model used in the AIRS retrieval system V4.0 required a 2% increase in methane absorption coefficients for strong absorption channels, and this bias adjustment was implemented in the AIRS retrieval system V5.0. As a new operational product in V5.0, AIRS CH4 were validated using in situ aircraft observations at 22 sites of the NOAA Earth System Research Laboratory, Global Monitoring Division (NOAA/ESRL/GMD), ranging from the Arctic to the tropical South Pacific Ocean, but their altitudes are usually above 300 hPa. The results show the bias of the retrieved CH4 profiles for this version is −1.4∼0.1% and its RMS difference is about 0.5–1.6%, depending on altitude. These validation comparisons provide critical assessment of the retrieval algorithm and will continue using more in situ observations together with future improvement to the retrieval algorithm. AIRS CH4 products include not only the CH4 profile but also the information content. As examples, the products of AIRS CH4 in August 2004 and the difference of CH4 in May and September 2004 are shown. From these results a few features are evident: (1) a large AIRS CH4 plume southwest of the Tibetan plateau that may be associated with deep convection during the Asian summer monsoon; (2) high mixing ratios of AIRS CH4 in southeastern Asia and in the high northern hemisphere in the summer; and (3) the increase of AIRS CH4 from May to September in the high northern hemisphere that is likely linked with wetland emission but needs more study. Further analysis of these data and its comparison with model data will be addressed in a separate paper.
Continuous increases in the human population and human activities have resulted in remarkable changes in the composition of the atmosphere since the industrial revolution ...
Ozone (O3) is a very important atmospheric component related to many atmospheric processes. The Tibetan Plateau (TP) has played an important role to weather and climate in South Asia and was found to ...modulate the variation of ozone amount, leading to a low-ozone event over the TP in both summer and winter. To better understand the changing trend of ozone, a novel statistic method, that is, the ensemble empirical mode decomposition method, is used to analyze the trends of total column O3 (TCO) and the ozone deficit after removing the corresponding zonal mean of TCO over the TP. Data of TCO over the TP from satellite observations by Ozone Monitoring Instrument/Aura from 2004 to 2019 and Ozone Mapping and Profiler Suite/S-NPP from 2013 to 2019 are used, and, for comparison, the long-term merged ozone data from NASA are used to analyze the trend of TCO in three latitude zones of 25°N–30°N, 30°N–35°N, and 35°N–40°N near the TP. In consistent with some other studies, a slight recovery of ozone around 1996–1997 is evident, with the peak occurring in 2000, but the rate is near zero in 2005. The mean annual trends over 30°N–35°N are −0.836 ± 0.233 DU/yr during 1979–1996 and 0.021 ± 0.124 DU/yr during 1997–2018. Based on the Ozone Monitoring Instrument data, TCO over the TP 27.5°N–37.5°N, 75.5°E–105.5°E shows a consistent increase trend from 2005 to 2019, and the ozone deficit starts to increase since 2009, indicating that the ozone increase rate over TP is larger than the zonal average. The ozone deficit over the TP shows an even more rapid increase trend after 2015, with a larger increase during winter than summer. Further analysis of the low-ozone event in winter and early summer (MJJ) from 2004 to 2019 shows that the low-ozone event in May is much deeper than that in winter and also lasts longer than that in February. This study confirms the mechanism of the winter low-ozone event over the TP is more complex than that in summer. This finding of more and faster increase in ozone over the TP relative to the zonal mean suggests the possibility of the decrease in the ultraviolet radiation over the TP, which will benefit human skin health and biosphere over the TP; therefore, it is important to continue to monitor the ozone trend and study its mechanism.
We perform a demonstration experiment using the National Oceanic Atmospheric Administration Unique Cross-track Infrared Sounder (CrIS)/Advanced Technology Microwave Sounder Processing System to ...assess the improvement on trace gas retrievals upon switching to high spectral resolution CrIS radiance measurements (0.625 cm -1 ). The focus of this study is carbon monoxide retrievals. The experimental high spectral resolution CO retrievals show a remarkable improvement, of almost up to one order of magnitude in the degree of freedom of the signal, with respect to the low-resolution mode. Furthermore, high-resolution CO retrievals show similar skill with respect to existing CO operational products from the Atmospheric InfraRed Sounder, Atmospheric Sounder Interferometer, and Measurements of Pollution In The Troposphere instruments, both in terms of spatial variability and degrees of freedom. The results of this research provide evidence to support the need for high spectral resolution CrIS measurements. This is a fundamental prerequisite in guaranteeing continuity to the CO afternoon orbit monitoring as part of a multisatellite uniformly integrated long-term data record of atmospheric trace gases.
Satellite-based hyper-spectral infrared (IR) sensors such as the Atmospheric Infrared Sounder (AIRS), the Cross-track Infrared Sounder (CrIS), and the Infrared Atmospheric Sounding Interferometer ...(IASI) cover many methane (CH4) spectral features, including the ν1 vibrational band near 1300 cm−1 (7.7 μm); therefore, they can be used to monitor CH4 concentrations in the atmosphere. However, retrieving CH4 remains a challenge due to the limited spectral information provided by IR sounder measurements. The information required to resolve the weak absorption lines of CH4 is often obscured by interferences from signals originating from other trace gases, clouds, and surface emissions within the overlapping spectral region. Consequently, currently available CH4 data product derived from IR sounder measurements still have large errors and uncertainties that limit their application scope for high-accuracy climate and environment monitoring applications. In this paper, we describe the retrieval of atmospheric CH4 profiles using a novel spectral fingerprinting methodology and our evaluation of performance using measurements from the CrIS sensor aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite. The spectral fingerprinting methodology uses optimized CrIS radiances to enhance the CH4 signal and a machine learning classifier to constrain the physical inversion scheme. We validated our results using the atmospheric composition reanalysis results and data from airborne in situ measurements. An inter-comparison study revealed that the spectral fingerprinting results can capture the vertical variation characteristics of CH4 profiles that operational sounder products may not provide. The latitudinal variations in CH4 concentration in these results appear more realistic than those shown in existing sounder products. The methodology presented herein could enhance the utilization of satellite data to comprehend methane’s role as a greenhouse gas and facilitate the tracking of methane sources and sinks with increased reliability.
It has been found that the concentration of atmospheric methane (CH4) has rapidly increased since 2007 after a decade of nearly constant concentration in the atmosphere. As an important greenhouse ...gas, such an increase could enhance the threat of global warming. To better quantify this increasing trend, a novel statistic method, i.e. the Ensemble Empirical Mode Decomposition (EEMD) method, was used to analyze the CH4 trends from three different measurements: the mid–upper tropospheric CH4 (MUT) from the space-borne measurements by the Atmospheric Infrared Sounder (AIRS), the CH4 in the marine boundary layer (MBL) from NOAA ground-based in-situ measurements, and the column-averaged CH4 in the atmosphere (XCH4) from the ground-based up-looking Fourier Transform Spectrometers at Total Carbon Column Observing Network (TCCON) and the Network for the Detection of Atmospheric Composition Change (NDACC). Comparison of the CH4 trends in the mid–upper troposphere, lower troposphere, and the column average from these three data sets shows that, overall, these trends agree well in capturing the abrupt CH4 increase in 2007 (the first peak) and an even faster increase after 2013 (the second peak) over the globe. The increased rates of CH4 in the MUT, as observed by AIRS, are overall smaller than CH4 in MBL and the column-average CH4. During 2009–2011, there was a dip in the increase rate for CH4 in MBL, and the MUT-CH4 increase rate was almost negligible in the mid-high latitude regions. The increase of the column-average CH4 also reached the minimum during 2009–2011 accordingly, suggesting that the trends of CH4 are not only impacted by the surface emission, however that they also may be impacted by other processes like transport and chemical reaction loss associated with OH. One advantage of the EEMD analysis is to derive the monthly rate and the results show that the frequency of the variability of CH4 increase rates in the mid–high northern latitude regions is larger than those in the tropics and southern hemisphere.
China's industrialized regions have seen increasing occurrence of heavy haze caused by severe particle pollution. However, aerosol retrieval under these circumstances is often excluded from NASA's ...Moderate Resolution Imaging Spectrometer (MODIS) aerosol products due to cloud mask and suspected high surface reflectance. An algorithm to retrieve the haze aerosol optical thickness (HAOT) is developed using MODIS data to supplement the current MODIS retrieval algorithm. This method includes 1) haze identification, 2) the generation of a surface reflectance database using MODIS data in hazy conditions, and 3) the development of haze aerosol models with four aerosol components simulated by a global 3-D atmospheric chemical transport model (GEOS-Chem). This algorithm was used in combination with the MODIS dense dark vegetation algorithm to retrieve 1 km HAOT over North China Plain from March to September of 2008. The values of the retrieved HAOT values are mostly between 0.7-3, with a correlation coefficient of 0.82 with the Aerosol Robotic NETwork observations and a 19% mean relative difference. Retrieval uncertainties associated with the errors in haze detection, surface reflectance, and haze models were analyzed using ground measurements.
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