Research On Spatiotemporal Formaldehyde Variation Analysis And Prediction,Retrieval And Occultation Detection Pointing Information Determination Algorithms

Here,the distribution and characteristics of HCHO in eastern China,prediction approach and retrieval algorithms were studied.In addition,the feasiability of HCHO profile retrieval was discussed and the tangent height for occultation observation was corrected.?1?The widespread distribution and strong seasonal pattern of highly concentrated summertime formaldehyde?HCHO?were observed using data from the Ozone Monitoring Instrument?OMI?onboard Aura satellite from 2005 to 2015 in Beijing-Tianjin-Hebei,China.The large-scale HCHO concentrations and its close connection with the surface O₃ pollution made the study of summertime HCHO patterns and its major contributors necessary.Accordingly,time series decomposition,Moran's I and Pearson correlation coefficient?PCC?were adopted to investigate the spatiotemporal variations of HCHO.We found that the HCHO columns regionally increased from 2005to 2010 and decreased in the north?e.g.,Chengde?from 2010 to 2015.Additionally,HCHO Vertical Column Densities?VCDs?exhibited higher values in urban areas.Despite the strong possibilities of major biogenic contributions,anthropogenic sources represented larger spatial PCCs and larger total emission rates.Industrial sources exhibited a large increasing emission amount,and the most similar distribution to HCHO was found in residential sources.By comparison,power-based emissions accounted for a relatively small fraction,and transportation emissions declined rapidly.In conclusion,anthropogenic VOCs might contribute to the summertime HCHO concentrations as well as isoprene,and controls on VOCs and HCHO would be greatly assisted by the satellite-based observations.1.Objectives:High-level tropospheric formaldehyde?HCHO?columns were observed over Guangdong Province and Jiangsu Province in China by using a long-term record?2005 to 2016?of Aura OMI measurements.Due to the socioeconomic values of Guangdong Province and Jiangsu Province,research concerning the widespread air-pollution issues throughout these regions is imperative.Accordingly,the spatiotemporal variations in HCHO and the potential contributors were analyzed.2.Method:To investigate region of interest in various spatial resolutions;that is,we studied spatiotemporal characteristics of HCHO columns over province-level and in prefecture-level-cites.To achieve this,the administrative shapefiles were used to clip HCHO distributions to represent various sample regions.The spatial resolution of the OMI monthly gridded HCHO columns is 0.25°×0.25°,but some ancillary data have finer resolutions than that of the Level-3 gridded HCHO columns.Accordingly,the inverse distance weighted interpolation algorithm and KD-Tree method were adopted for re-sampling finer spatial resolutions into 0.25°×0.25°.The linear least squares regression adopted in this study is the approach to infer the potential trends exhibited in HCHO images,the trends were fitted pixel-by-pixel and the regional trends were calculated by zonal averaging over the administrative regions selected in the aforementioned shapefiles.Spearman Correlation Coefficients were employed to evaluate the similarity of HCHO distribution and that of multitude sources?e.g.,isoprene,anthropogenic VOCs?3.Result:In Guangdong Province,HCHO columns mainly concentrated in the Pearl River Delta?PRD?,but a more widespread distribution was observed in Jiangsu Province.An upward trend was found in both provinces from2005 to 2010 that might be closely related to the rapid economy development in that period.In contrast,from 2011 to 2016,an overall downward trend was observed over these two regions,given the multitude controls enacted.In term of seasonality,the highest HCHO columns showed in spring and autumn while the summertime HCHO had the lowest concentration in Guangdong,whilst HCHO seasonal patterns corresponded to the seasonal patterns of sunlight intensity.Among all source sectors,industrial and transportation might contribute the most in the PRD,but all sectors might contribute in the same order of magnitude in Jiangsu.In addition,biogenic sources might have a comparative large contribution in the northeastern Guangdong and the biomass burning in summertime possibly played a magnificent role in summertime HCHO concentration over Jiangsu Province.4.Conclusion:Although isoprene plays a significant role in HCHO concentration in global scale,the anthropogenic impact cannot be neglected as well.According to previous studies,anthropogenic sources impose influence for more than 40%.In addition,compared with isoprene,the Spearman Correlation Coefficients were higher for anthropogenic VOCs with HCHO columns.Given the relatively large amount of emissions,industrial sources might be influential for more than 40%.Biomass burning sources cannot be ignored in woodlands like northeastern Guangdong.Transportation sources exhibited the most similar Spearman Correlation Coefficients in Guangdong,especially in PRD.Therefore,even a downward trend of transportation emissions was observed over PRD,they might account for a large amount of HCHO concentration.By comparison,power-based emissions only took a small fraction about 1%for both Guangdong and Jiangsu.?2?Formaldehyde?HCHO?is a short lived harmful trace gas and closely related to photochemical reaction and surface O₃ pollution formation.Guangdong Province,especially PRD is the most severe HCHO polluted region in China.Lacking of regular in-situ observation makes the daily satellite based measurements?i.e.,GOME-2/MetOp-B?as a significant alternative method.However,because of clouds,satellite revisit period and other reasons,data of some days is missing and this also causes difficulties in prediction.A method to solve this is using modeling simulation?i.e.,CMAQ HCHO simulation?as a supplement of missing satellite measurements.In this study,UKF was presented to conduct data padding and two neural network models?i.e.,MLP and LSTM?were adopted to train and predict HCHO columns.Results illustrated that the correlation between GOME-2 test sets and filtered test sets was improved at least 10 times and the correlation of test sets was higher than 0.9 after the elimination of outliers.Findings indicated that the proposed methods improve the availability of CMAQ HCHO simulation.Besides,the easy-to-use and robust neural network models make the operational use in prediction more available.?3?Formaldehyde?HCHO?is a toxic trace gas and carcinogen that mainly concentrates in atmospheric planetary layer.The lifetime of HCHO is short at an order of several hours.Anthropogenic VOC gradually becomes a negligible part of air pollution in China and HCHO is an important indicator of VOC.Apparently,the investigation of HCHO is very valuable.Due to the lack of in situ observations for HCHO,satellite-based remote sensing proving frequent and large coverage measurements becomes a significant alternative.In this study,we discussed the characteristics of atmospheric HCHO in eastern China and furthermore we discussed the payloads for HCHO detection and retrieval theories.From the last century,payloads commonlyavailableforHCHOdetectionareGOME/ERS-2,SCIAMACHY/ENVISAT,OMI/Aura,GOME-2/MetOp-A?B?,OMPS/Suomi-NPP.We reviewed relative information about satellite orbits,spatiotemporal resolution and appliance in HCHO retrieval.Because of the top-down observation of satellite platform which is different to the bottom-up of in situ observation,the retrieval algorithms are different as well.Apparently,we focused on two majorly adopted methods for HCHO retrieval:differential optical absorption spectroscopy?DOAS?and recently proposed principal component analysis?PCA?.?4?As compared to nadir observations,occultation observations offer improved vertical resolution for deriving profiles of pressure/temperature and of atmospheric species.Reliable pointing information in terms of tangent heights is indispensable to the accurate retrievals of atmospheric profiles.A fast,geometrical tangent height correction algorithm was proposed,and it features triangular-net iteration.This study employs the proposed algorithm for the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer?ACE-FTS?which has similar characteristics with China's planned occultation instrument.To meet the requirement of operational environment,several treatments?e.g.,tangential stride generator and triangular-net optimization?were adopted based on N₂ absorption microwindows.In experiments on three ACE-FTS orbits,the algorithm exhibits a satisfactory performance and is in good agreement with the official Level-2 tangent height products?i.e.,the average correlation coefficient is greater than 0.98?.In addition,relative uncertainties are 1.18 km,0.66 km and 1.23 km for three orbits,respectively.Whilst averaged quadratic sum loss is⁰.07,the average computation time is about 16.6 minutes,thereby the correction effectiveness is acceptable and the design of this approach proposed is plausible in some levels.