Moderate Resolution Imaging Spectroradiometer Aerosol Optical Thickness Research Articles

Analysis of total column ozone, water vapour and aerosol optical thickness over Ahmedabad, India

ABSTRACTA preliminary study was performed to investigate the quality of total column ozone (TCO), water vapour (WV) and aerosol optical thickness (AOT) available from satellite and reanalysis from atmospheric models along with in situ observations over Ahmedabad (23.03 ° N, 72.5 ° E, 55 m above mean sea level), India. Ground‐based measurements from a MICROTOPS II ozonometer as well as space‐based satellite retrieved products from the moderate resolution imaging spectroradiometer (MODIS) and an ozone monitoring instrument were analysed during December 2014 to March 2015. The European Centre for Medium‐Range Weather Forecasts (ECMWF) reanalysis (ERA‐Interim) created TCO and WV were also used to assess the skill of global model reanalysis over the western part of India. An increasing trend was found in the TCO and WV parameters from the winter to summer period. Investigations showed that MODIS satellite retrieved and ERA‐Interim reanalysis WV are able to capture the trends compared with ground‐based hand‐held MICROTOPS II observations. Higher TCO was found in the MODIS data, whereas the ERA‐Interim and ozone monitoring instrument TCO matched well with ground‐based observations. Larger differences were found with the MODIS AOT in comparison to MICROTOPS II AOT observations. Further, analysis showed that ERA‐Interim has sufficient potential to be used for various meteorological applications over the western Indian region. Furthermore, the variations of TCO, WV and AOT were studied over the orographic region of Mount Abu (∼110 km aerial distance from Ahmedabad), located in the Aravali range of mountains. Ground‐based measurements at different altitudes (0.3, 1.1 and 1.67 km above mean sea level) revealed significant variations in WV and AOT. The WV varies 17.1% (30.3%) and the AOT varies 53.8% (57.5%) in 1.1 km (1.67 km), whereas no noteworthy variations are observed in the TCO in this field campaign.

Mapping exposure to particulate pollution during severe haze episode using improved MODIS AOT-PM10 regression model with synoptic meteorology classification.

Severe smoke haze from biomass burning is frequently observed in Northern Thailand during dry months of February–April. Sparsely located monitoring stations operated in this vast mountainous region could not provide sufficient particulate matter (PM) data for exposure risk assessment. Satellite aerosol optical thickness (AOT) data could be used, but their reliable relationship with ground‐based PM data should be first established. This study aimed to improve the regression model between PM10 and Moderate Resolution Imaging Spectroradiometer AOT with consideration of synoptic patterns to better assess the exposure risk in the area. Among four synoptic patterns, each representing the totality of meteorology governing Northern Thailand on a given day, most severe haze days belonged to pattern 2 that featured conditions of clear sky, stagnant air, and high PM10 levels. AOT‐24 h PM10 regression model for pattern 2 had coefficient of determination improved to 0.51 from 0.39 of combined case. Daily exposure maps to PM10 in most severe haze period of February–April 2007 were produced for Chiangmai, the largest and most populated province in Northern Thailand. Regression model for pattern 2 was used to convert 24 h PM10 ranges of modified risk scale to corresponding AOT ranges, and the mapping was done using spatially continuous AOT values. The highest exposure risk to PM10 was shown in urban populated areas. Larger numbers of forest fire hot spots and more calm winds were observed on the days of higher exposure risk. Early warning and adequate health care plan are necessary to reduce exposure risk to future haze episodes in the area.

Exploiting TERRA-AQUA MODIS Relationship in the Reflective Solar Bands for Aerosol Retrieval

Satellite remote sensing has been providing aerosol data with ever-increasing accuracy, representative of the MODerate-resolution Imaging Spectroradiometer (MODIS) Dark Target (DT) and Deep Blue (DB) aerosol retrievals. These retrievals are generally performed over spectrally dark objects and therefore may struggle over bright surfaces. This study proposed an analytical TERRA-AQUA MODIS relationship in the reflective solar bands for aerosol retrieval. For the relationship development, the bidirectional reflectance distribution function (BRDF) effects were adjusted using reflectance ratios in the MODIS 2.13 μm band and the path radiance was approximated as an analytical function of aerosol optical thickness (AOT) and scattering phase function. Comparisons with MODIS observation data, MODIS AOT data, and sun photometer measurements demonstrate the validity of the proposed relationship for aerosol retrieval. The synergetic TERRA-AQUA MODIS retrievals are highly correlated with the ground measured AOT at TERRA MODIS overpass time (R2 = 0.617; RMSE = 0.043) and AQUA overpass time (R2 = 0.737; RMSE = 0.036). Compared to our retrievals, both the MODIS DT and DB retrievals are subject to severe underestimation. Sensitivity analyses reveal that the proposed method may perform better over non-vegetated than vegetated surfaces, which can offer a complement to MODIS operational algorithms. In an analytical form, the proposed method also has advantages in computational efficiency, and therefore can be employed for fine-scale (relative to operational 10 km MODIS product) MODIS aerosol retrieval. Overall, this study provides insight into aerosol retrievals and other applications regarding TERRA-AQUA MODIS data.

Spaceborne observations of low surface aerosol concentrations in the Stockholm region

This article investigates the feasibility of using spaceborne observations of aerosol optical thickness (AOT) derived with the Moderate Resolution Imaging Spectroradiometer (MODIS) for monitoring of fine particulate matter (PM2.5) in an environment of low aerosol loading. Previous studies of the AOT-to-PM2.5 relationship benefit from the large range of observed values. The Stockholm region features a comprehensive network of ground-based monitoring stations that generally show PM2.5 values <20 µg m−3. MODIS AOT at 555 nm is usually <0.20 and in good agreement with ground-based sun photometer observations in this region. We use MODIS Collection 5 AOT data with a horizontal resolution of 10 km×10 km and ground-based in-situ PM2.5 observations to derive an AOT-to-PM2.5 relationship that can be used to estimate fields of PM2.5. This has been carried out with respect to the months from April to September of the period 2000–2013. Relative average absolute deviations of 33–55 % (mean of 45 %) are obtained between MODIS-retrieved and ground-based PM2.5. The root mean square error is 0.2159 µg m−3 between retrieved and measured PM2.5. From spaceborne lidar observations, it is found that elevated aerosol layers are generally sparse in the Stockholm region. This favours remote sensing of PM2.5 from space. The deviations found between measured and retrieved PM2.5 are mainly attributed to infrequent situations of inhomogeneous aerosol layering for which column-integrated observations cannot be connected to surface conditions. Using MODIS Collection 6 data with a resolution of 3 km×3 km in a case study actually gives far fewer results than the coarser Collection 5 product. This is explained by the complex geography of the Stockholm region with a coastline and an abundance of lakes, which seems to induce biases in the retrieval of AOT at higher spatial resolution.

Suomi-NPP위성 DNB관측을 이용한 우리나라 소도시에서의 야간 에어로졸 광학두께 추정

Abstract : In this study, an algorithm to estimate Aerosol Optical Thickness (AOT) over small citiesduring nighttime has been developed by using the radiance from artificial light sources in small citiesmeasured from Visible Infrared Imaging Radiometer Suite (VIIRS) sensor’s Day/Night Band (DNB)aboard the Suomi-National Polar Partnership (Suomi-NPP) satellite. The algorithm is based on Beer’sextinction law with the light sources from the artificial lights over small cities. AOT is retrieved for cloud-free pixels over individual cities, and cloud-screening was conducted by using the measurements fromM-bands of VIIRS at infrared wavelengths. The retrieved nighttime AOT is compared with the aerosolproducts from MODerate resolution Imaging Spectroradiometer (MODIS) aboard Terra and Aquasatellites. As a result, the correlation coefficients over individual cities range from around 0.6 and 0.7between the retrieved nighttime AOT and MODIS AOT with Root-Mean-Squared Difference (RMSD)ranged from 0.14 to 0.18. In addition, sensitivity tests were conducted for the factors affecting the nighttimeAOT to estimate the range of uncertainty in the nighttime AOT retrievals. The results of this study indicatethat it is promising to infer AOT using the DNB measaurements over small cities in Korea at night. Afterfurther development and refinement in the future, the developed retrieval algorithm is expected to producenighttime aerosol information which is not operationally available over Korea.Key Words : Aerosol, Nighttime Aerosol Optical Thickness, Day Night Band요약 :

Using SEVIRI fire observations to drive smoke plumes in the CMAQ air quality model: a case study over Antalya in 2008

Abstract. Among the atmospheric emission sources, wildfires are episodic events characterized by large spatial and temporal variability. Therefore, accurate information on gaseous and aerosol emissions from fires for specific regions and seasons is critical for air quality forecasts. The Spinning Enhanced Visible and Infrared Imager (SEVIRI) in geostationary orbit provides fire observations over Africa and the Mediterranean with a temporal resolution of 15 min. It thus resolves the complete fire life cycle and captures the fires' peak intensities, which is not possible in Moderate Resolution Imaging Spectroradiometer (MODIS) fire emission inventories like the Global Fire Assimilation System (GFAS). We evaluate two different operational fire radiative power (FRP) products derived from SEVIRI, by studying a large forest fire in Antalya, Turkey, in July–August 2008. The EUMETSAT Land Surface Analysis Satellite Applications Facility (LSA SAF) has higher FRP values during the fire episode than the Wildfire Automated Biomass Burning Algorithm (WF_ABBA). It is also in better agreement with the co-located, gridded MODIS FRP. Both products miss small fires that frequently occur in the region and are detected by MODIS. Emissions are derived from the FRP products. They are used along-side GFAS emissions in smoke plume simulations with the Weather Research and Forecasting (WRF) model and the Community Multiscale Air Quality (CMAQ) model. In comparisons with MODIS aerosol optical thickness (AOT) and Infrared Atmospheric Sounding Interferometer (IASI), CO and NH3 observations show that including the diurnal variability of fire emissions improves the spatial distribution and peak concentrations of the simulated smoke plumes associated with this large fire. They also show a large discrepancy between the currently available operational FRP products, with the LSA SAF being the most appropriate.

MODIS 에어러솔 광학두께와 지상에서 관측된 시정거리를 이용한 대기 에어러솔 연직분포 산출

본 연구에서는 MODIS 인공위성으로 분석된 에어러솔 광학두께 자료와 지상에서 관측된 시정거리 자료를 이용하여 에어러솔 연직분포 모델링을 수행하였다. 위성과 지상관측자료로부터 에어러솔의 척도 고도를 구할 수 있었으며, 그 결과는 복사전달 모델에서 사용되고 있는 표준대기 모델과 비교에서 만족할 만한 수준의 근사치를 보였다. 그리고 실제 사례로서 대기가 청명한 경우(<TEX>${\tau}_{MODIS}=0.12{\pm}0.07$</TEX>, 시정거리=<TEX>$21.13{\pm}3.31km$</TEX>)와 혼탁한 경우(<TEX>${\tau}_{MODIS}=1.71{\pm}0.85$</TEX>, 시정거리 =<TEX>$13.33{\pm}5.66km$</TEX>)에 대해서 적용하여 척도 고도를 산정한 결과는 각각 전국 평균값으로서 <TEX>$0.63{\pm}0.33km$</TEX>와 <TEX>$1.71{\pm}0.84km$</TEX>로 나타났다. 그리고 이 결과를 바탕으로 대기 에어러솔 소산계수의 연직분포를 구할 수 있었으며, 최종적으로 KML 형식으로 코딩되어 관심 영역의 대기 환경 특성 변화를 감시하는데 도움이 될 것으로 기대된다. This study presents a modeling of aerosol extinction vertical profiles in Korea by using the Moderate Resolution Imaging Spectro-radiometer(MODIS) derived aerosol optical thickness(AOT) and ground based visibility observation data. The method uses a series of physical equations for the derivation of aerosol scale height and vertical profiles from MODIS AOT and surface visibility data. The modelled results under the standard atmospheric condition showed small differences with the standard aerosol vertical profile used in the radiative transfer model. Model derived aerosol scale heights for two cases of clean(<TEX>${\tau}_{MODIS}=0.12{\pm}0.07$</TEX>, visibility=<TEX>$21.13{\pm}3.31km$</TEX>) and hazy atmosphere(<TEX>${\tau}_{MODIS}=1.71{\pm}0.85$</TEX>, visibility=<TEX>$13.33{\pm}5.66km$</TEX>) are <TEX>$0.63{\pm}0.33km$</TEX> and <TEX>$1.71{\pm}0.84km$</TEX>. Based on these results, aerosol extinction profiles can be estimated and the results are transformed into the KML code for visualization of dataset. This has implications for atmospheric environmental monitoring and environmental policies for the future.

Analysis of Spatial and Temporal Variability of PM10 Concentrations Using MODIS Aerosol Optical Thickness in the Pearl River Delta Region, China

Characterizing spatial and temporal variations of PM pollution is critical for a thorough understanding of its formation, transport and accumulation in the atmosphere. In this study, Aerosol Optical Thickness (AOT) data retrieved from a Moderate Resolution Imaging Spectroradiometer (MODIS) were used to investigate the spatial and temporal variations of PM10 (particles with aerodynamic diameters of less than 10 μm) pollution in the Pearl River Delta (PRD) region. Seasonal linear regression models between 1-km retrieved MODIS AOT data and ground PM10 measurements were developed for the PRD region with meteorological corrections, and were subjected to a validation against observations from the regional air monitoring network in this region from 2006 to 2008, with an overall error of less than 50%. Consistent with ground observations, the estimated PM10 concentrations from the regression models appeared to be highest in winter, lower in autumn and spring, and lowest in summer. A high PM10 concentration band was detected over the inner part of the PRD region, where heavy industries and dense populations are located. The shape and concentration levels of this band exhibit significant seasonal variations, which shift with synoptic wind direction, indicating different source regions and their contributions to the PM10 pollution in the PRD region. Several discrete “hot spots” were found in the southwest of the PRD region during spring and other seasons, where no ground measurements are available. The reasons for the formation of these hot spots are unclear, and further investigations are needed. Despite the limitations of this work, the results demonstrate the effectiveness of retrieving remote sensing data for characterizing regional aerosol pollution, together with ground measurements. The combination of satellite data and ground monitoring presented in this work can help in better understanding the sources, formation mechanisms and transport process of particulate matters on a regional scale.

Characteristics of Aerosol Optical Thickness as Well as the Relationship with NDVI in the Yangtze River Delta, China

A long term (2000 - 2008) dataset of aerosol products retrieved from MODerate Resolution Imaging Spectroradiometer (MODIS) is used to investigate the temporal and spatial variations of aerosol optical thickness (AOT) over the Yangtze River Delta (YRD). Ground-based observations (sun photometers) were used to validate the MODIS L2 aerosol products, and the Normalized Difference Vegetation Index (NDVI) derived from SPOT-VGT is used to analyze the relationship with AOT. The results illustrate that the highest correlation (R = 0.92) of CE-318 AOT vs. MODIS AOT is in Hangzhou with the slope and intercept of 1.04 and -0.01. The largest value of AOT appears in June, and has the largest spatial differences in July. There are two different aerosol patterns. One includes smaller AOT over dense vegetation cover areas dominated by natural aerosols and the other involves larger AOT over urban areas where anthropogenic aerosols dominate. The correlation analysis indicates that there are moderate negative correlation coefficients (R) for AOT vs. NDVI, and the R values vary as seasons shift. The range of R values is 0 ~ -0.8 and the mean values are about -0.5. The relationship between AOT and NDVI is more obvious in dense vegetation areas.

A Study of Dust Aerosols Impact on Hurricanes with Multi-Sensors Measurement from Space

MODerate resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Thickness (AOT) and the Atmospheric Infrared Sounder (AIRS) atmospheric profiles (temperature and moisture) Level 2 products are studied to investigate dust aerosols impacts on hurricanes through spatial analysis. Spatial regions were selected based on two concentric circles (an annulus) and segmented by left and right regions of 180° each around the hurricanes center. Statistical relationships between MODIS AOT, AIRS temperature and percent relative humidity (RH) of the hurricanes Isabel (2003), Frances (2004), Katrina (2005) and Helene (2006) are presented. The variation of temperature and RH values represented in static-left, static-right, dynamic-left and dynamic-right for the 500 mb, 700 mb and 850 mb pressure levels are analyzed to determine the impacts of dust aerosols on temperature and RH. Average AOT was found highest in Helene (0.27) than Isabel (0.23), Frances (0.18) and Katrina (0.16). Negative impacts on the atmospheric moisture levels and positive on the temperature was found by dust aerosols. This study concludes that in 2006 dust dampened the force of hurricane Helene contributing towards extremely dryer atmosphere and inhibiting the conductive to intensify the hurricane.

Satellite remote sensing analysis of the 2010 Eyjafjallajökull volcanic ash cloud over the North Sea during 4–18 May 2010

Using the Moderate Resolution Imaging Spectroradiometer (MODIS), Spinning Enhanced Visible and Infrared Imager (SEVIRI), Clouds and the Earth's Radiant Energy System (CERES) instrument, and BaE146 aircraft data sets, we provide an overview of volcanic ash spatial distribution for six days (4–18 May 2010) and assess their properties and radiative impacts for 17 May primarily over the North Sea. We describe spectral signatures of volcanic ash, compare the MODIS‐retrieved 550 nm aerosol optical thickness (AOT) and effective radii with the aircraft data, and then assess the change in radiative fluxes at the top of atmosphere using CERES. Our results indicate that the MODIS and SEVIRI thermal channels are adept at identifying volcanic ash near the source. However, the volcanic ash far from the volcanic source, especially over land, is contaminated by surface/atmospheric features. We assess the 17 May case in detail and show that MODIS AOTs (0.23–0.86) are higher than the aircraft values (0.07–0.54), probably due to different aerosol models used in the retrieval process. The MODIS effective radii values are between 0.4 and 0.9 μm with fine mode fraction values between 0.4 and 0.7. The aircraft‐derived effective radii values are between 0.82 and 1.2 μm. The TOA shortwave radiative forcing for unit AOT of volcanic ash aerosols at the time of the satellite overpass is −77 ± 4.0 W m−2 and is larger than the longwave forcing per unit optical depth (11 ± 1.2 W m−2) by seven times indicating that ash could significantly impact radiative energy fluxes.

Simultaneous determination of aerosol optical thickness and surface reflectance using ASTER visible to near-infrared data over land

An innovative method for the determination of aerosol optical thickness (AOT) and surface reflectance for operational use of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) visible to near-infrared data is presented. This method is designed to obtain the atmospheric parameters needed in the correction of the image. This method is based on a simplified radiative transfer equation describing the relation between the ground surface reflectance, AOT and top-of-atmosphere reflectance. By exploiting the ASTER dual-angle view capabilities in band 3N (Nadir) and band 3B (Backwards), surface reflectance and AOT can be retrieved synchronously. Thus, it solves the problem of separating atmospheric radiance from the transmitted radiance of the surface to some extent. After applying this new atmospheric correction method to three areas of ASTER images, Beijing urban city, the Heihe River Basin and Hong Kong of China, ASTER surface reflectance products (AST07) were obtained. AOT values from in situ measurements of CIMEL Electronique 318 Sun Photometers or AERONET (AErosol RObotic NETwork) and surface reflectance in situ measured using an Analytical Spectral Device (ASD) Field Spec spectral radiometer are used for validation. AOT derived from the new method is consistent with in situ station measurements from CIMEL Electronique 318 Sun Photometer and level 2.0 data from AERONET, with correlation coefficient (R 2) of 0.98 and root mean square error of 0.05, whereas Multi-angle Imaging Spectroradiometer AOT products underestimate AERONET AOT and Moderate-Resolution Imaging Spectroradiometer AOT products overestimate AERONET AOT in these regions. More encouraging is the comparison between the corrected surface reflectance, AST07 and ASD measurements. Root mean square error of AST07 and retrieved surface reflectance are as follows: band 1 (556 nm) = 0.04 and 0.05; band 2 (661 nm) = 0.036 and 0.035; band 3 (807 nm) = 0.056 and 0.038, which suggests that compared with AST07 in bands 2 and 3, retrieved surface reflectance has better agreement with measured reflectance from ASD.

NASA A-Train and Terra observations of the 2010 Russian wildfires

Abstract. Wildfires raged throughout western Russia and parts of Eastern Europe during a persistent heat wave in the summer of 2010. Anomalously high surface temperatures (35–41 °C) and low relative humidity (9–25 %) from mid-June to mid-August 2010 shown by analysis of radiosonde data from multiple sites in western Russia were ideal conditions for the wildfires to thrive. Measurements of outgoing longwave radiation (OLR) from the Atmospheric Infrared Sounder (AIRS) over western Russian indicate persistent subsidence during the heat wave. Daily three-day back-trajectories initiated over Moscow reveal a persistent anti-cyclonic circulation for 18 days in August, coincident with the most intense period of fire activity observed by Moderate Resolution Imaging Spectroradiometer (MODIS). This unfortunate meteorological coincidence allowed transport of polluted air from the region of intense fires to Moscow and the surrounding area. We demonstrate that the 2010 Russian wildfires are unique in the record of observations obtained by remote-sensing instruments on-board NASA satellites: Aura and Aqua (part of the A-Train Constellation) and Terra. Analysis of the distribution of MODIS fire products and aerosol optical thickness (AOT), UV aerosol index (AI) and single-scattering albedo (SSA) from Aura's Ozone Monitoring Instrument (OMI), and total column carbon monoxide (CO) from Aqua's Atmospheric Infrared Sounder (AIRS) show that the region in the center of western Russia surrounding Moscow (52°–58° N, 33°–43° E) is most severely impacted by wildfire emissions. Over this area, AIRS CO, OMI AI, and MODIS AOT are significantly enhanced relative to the historical satellite record during the first 18 days in August when the anti-cyclonic circulation persisted. By mid-August, the anti-cyclonic circulation was replaced with westerly transport over Moscow and vicinity. The heat wave ended as anomalies of surface temperature and relative humidity, and OLR disappeared. After 18 August the fire activity greatly diminished over western Russia and levels of the satellite smoke tracers returned to values typical of previous years.

Effects of implementing satellite observed aerosols into a mesoscale atmosphere model

This study investigated the performance of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) in calculating the aerosol forcing on cloud cover, incoming surface solar radiation, and near-surface air temperature via the implementation of aerosol optical depth in the shortwave radiation parameterization. MM5 simulations with and without aerosol data are performed in the periods of 6–7 August 2003 and 19–21 September 2003 during which strong aerosol forcing was observed with Moderate Resolution Imaging Spectroradiometer (MODIS) data in the mid-Atlantic region. Both periods clearly showed that aerosols had a direct negative effect on surface solar radiation through aerosol scattering. For example, every 0.1 change in MODIS aerosol optical thickness (AOT) results in 44 and 59 W m−2 decreases in surface solar radiation for the first and second periods, respectively. A magnitude of 0.1 increment in MODIS AOT reduces air temperature 0.36 and 0.56 K for the first and second periods, respectively. Comparisons with satellite-derived surface solar radiation retrievals showed that aerosol implementation in MM5 consistently showed better incoming surface solar radiation than that of the non-aerosol case. This helps to reduce uncertainties related to the radiation–cloud–aerosol interaction in numerical weather modelling systems.

A study on the potential applications of satellite data in air quality monitoring and forecasting

In this study we explore the potential applications of MODIS (Moderate Resolution Imaging Spectroradiometer) -like satellite sensors in air quality research for some Asian regions. The MODIS aerosol optical thickness (AOT), NCEP global reanalysis meteorological data, and daily surface PM10 concentrations over China and Thailand from 2001 to 2009 were analyzed using simple and multiple regression models. The AOT–PM10 correlation demonstrates substantial seasonal and regional difference, likely reflecting variations in aerosol composition and atmospheric conditions. Meteorological factors, particularly relative humidity, were found to influence the AOT–PM10 relationship. Their inclusion in regression models leads to more accurate assessment of PM10 from spaceborne observations. We further introduced a simple method for employing the satellite data to empirically forecast surface particulate pollution. In general, AOT from the previous day (day 0) is used as a predicator variable, along with the forecasted meteorology for the following day (day 1), to predict the PM10 level for day 1. The contribution of regional transport is represented by backward trajectories combined with AOT. This method was evaluated through PM10 hindcasts for 2008–2009, using observations from 2005 to 2007 as a training data set to obtain model coefficients. For five big Chinese cities, over 50% of the hindcasts have percentage error ≤ 30%. Similar performance was achieved for cities in northern Thailand. The MODIS AOT data are responsible for at least part of the demonstrated forecasting skill. This method can be easily adapted for other regions, but is probably most useful for those having sparse ground monitoring networks or no access to sophisticated deterministic models. We also highlight several existing issues, including some inherent to a regression-based approach as exemplified by a case study for Beijing. Further studies will be necessary before satellite data can see more extensive applications in the operational air quality monitoring and forecasting.

Global satellite analysis of the relation between aerosols and short-lived trace gases

Abstract. The spatial and temporal correlations between concurrent satellite observations of aerosol optical thickness (AOT) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and tropospheric columns of nitrogen dioxide (NO2), sulfur dioxide (SO2), and formaldehyde (HCHO) from the Ozone Monitoring Instrument (OMI) are used to infer information on the global composition of aerosol particles. When averaging the satellite data over large regions and longer time periods, we find significant correlation between MODIS AOT and OMI trace gas columns for various regions in the world. This shows that these enhanced aerosol and trace gas concentrations originate from common sources, such as fossil fuel combustion, biomass burning, and organic compounds released from the biosphere. This leads us to propose that satellite-inferred AOT to NO2 ratios for regions with comparable photochemical regimes can be used as indicators for the relative regional pollution control of combustion processes. Indeed, satellites observe low AOT to NO2 ratios over the eastern United States and western Europe, and high AOT to NO2 ratios over comparably industrialized regions in eastern Europe and China. Emission databases and OMI SO2 observations over these regions suggest a much stronger sulfur contribution to aerosol formation than over the well-regulated areas of the eastern United States and western Europe. Furthermore, satellite observations show AOT to NO2 ratios are a factor 100 higher over biomass burning regions than over industrialized areas, reflecting the unregulated burning practices with strong primary particle emissions in the tropics compared to the heavily controlled combustion processes in the industrialized Northern Hemisphere. Simulations with a global chemistry transport model (GEOS-Chem) capture most of these variations, although on regional scales significant differences are found. Wintertime aerosol concentrations show strongest correlations with NO2 throughout most of the Northern Hemisphere. During summertime, AOT is often (also) correlated with enhanced HCHO concentrations, reflecting the importance of secondary organic aerosol formation in that season. We also find significant correlations between AOT and HCHO over biomass burning regions, the tropics in general, and over industrialized regions in southeastern Asia. The distinct summertime maximum in AOT (0.4 at 550 nm) and HCHO over the southeastern United States strengthens existing hypotheses that local emissions of volatile organic compounds lead to the formation of secondary organic aerosols there. GEOS-Chem underestimates the AOT over the southeastern United States by a factor of 2, most likely due to too strong precipitation and too low SOA yield in the model.

Short-wave aerosol radiative efficiency over the global oceans derived from satellite data

Using 5 yr (December 2000.November 2005) of satellite data from the clouds and the earths radiant energy system (CERES) and moderate resolution imaging spectroradiometer (MODIS), we examine the instantaneous short-wave radiative efficiency (Eτ) of aerosols during the morning Terra satellite overpass time over the global oceans (60.N. 60.S).We calculate Eτ using two commonly used methods. The first method uses the MODIS aerosol optical thickness (AOT) at 0.55 μm with radiative transfer calculations, whereas the second method utilizes the same AOT values along with a new generation of aerosol angular distribution models to convert the CERES-measured broad-band radiances to fluxes.Over the 5 yr, the global mean instantaneous Eτ between the methods is remarkably consistent and within 5W m-2 τ-1 with a mean value of .70W m-2 τ-1. The largest differences between the methods occur in high-latitude regions, primarily in the Southern Hemisphere, where AOT is low. In dust dominated regions, there is an excellent agreement between the methods with differences of Wm-2τ-1. These differences are largely due to assumptions in aerosol models and definition of clear sky backgrounds. Independent assessments of aerosol radiative effects from different satellite sensors and methods are extremely valuable and should be used to verify numerical modelling simulations.

Using numerical weather prediction errors to estimate aerosol heating

The total real response of the atmosphere to aerosols can be predicted by examining numerical models. In this study, the moderate resolution imaging spectroradiometer (MODIS) aerosol optical thickness (AOT) is correlated to model temperature errors to estimate this response for Israel and for Italy. Significant correlations between aerosols and atmospheric numerical model temperature errors are presented. Two main results were found in this study. First, the correlation between the UK Metrological Office (UKMO) model temperature error (ΔT) at level 850 hPa for Tel Aviv (Israel) during the year 2002 and the MODIS AOT ≥ 0.5, was found to be −0.54. Second, the sign of the correlation between the European Center for Medium-RangeWeather Forecasting (ECMWF) monthly averaged model surface temperature errors for Italy and the MODIS AOT depends on the aerosol type, as reflected by the specific area. The correlation between air surface ECMWF ΔT and AOT was found to be +0.70 in southern Italy. Although the contribution of aerosols is ignored by most models, the findings presented here are statistically significant and provide a first reliable estimation of the realistic full atmospheric temperature response to aerosol processes.

Improving correlations between MODIS aerosol optical thickness and ground-based PM 2.5 observations through 3D spatial analyses

The Center for Space Research (CSR) continues to focus on developing methods to improve correlations between satellite-based aerosol optical thickness (AOT) values and ground-based, air pollution observations made at continuous ambient monitoring sites (CAMS) operated by the Texas commission on environmental quality (TCEQ). Strong correlations and improved understanding of the relationships between satellite and ground observations are needed to formulate reliable real-time predictions of air quality using data accessed from the moderate resolution imaging spectroradiometer (MODIS) at the CSR direct-broadcast ground station. In this paper, improvements in these correlations are demonstrated first as a result of the evolution in the MODIS retrieval algorithms. Further improvement is then shown using procedures that compensate for differences in horizontal spatial scales between the nominal 10-km MODIS AOT products and CAMS point measurements. Finally, airborne light detection and ranging (lidar) observations, collected during the Texas Air Quality Study of 2000, are used to examine aerosol profile concentrations, which may vary greatly between aerosol classes as a result of the sources, chemical composition, and meteorological conditions that govern transport processes. Further improvement in correlations is demonstrated with this limited dataset using insights into aerosol profile information inferred from the vertical motion vectors in a trajectory-based forecast model. Analyses are ongoing to verify these procedures on a variety of aerosol classes using data collected by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite (Calipso) lidar.

Satellite remote sensing of particulate matter and air quality assessment over global cities

Using 1 year of aerosol optical thickness (AOT) retrievals from the MODerate resolution Imaging Spectro-radiometer (MODIS) on board NASA's Terra and Aqua satellite along with ground measurements of PM 2.5 mass concentration, we assess particulate matter air quality over different locations across the global urban areas spread over 26 locations in Sydney, Delhi, Hong Kong, New York City and Switzerland. An empirical relationship between AOT and PM 2.5 mass is obtained and results show that there is an excellent correlation between the bin-averaged daily mean satellite and ground-based values with a linear correlation coefficient of 0.96. Using meteorological and other ancillary datasets, we assess the effects of wind speed, cloud cover, and mixing height (MH) on particulate matter (PM) air quality and conclude that these data are necessary to further apply satellite data for air quality research. Our study clearly demonstrates that satellite-derived AOT is a good surrogate for monitoring PM air quality over the earth. However, our analysis shows that the PM 2.5–AOT relationship strongly depends on aerosol concentrations, ambient relative humidity (RH), fractional cloud cover and height of the mixing layer. Highest correlation between MODIS AOT and PM 2.5 mass is found under clear sky conditions with less than 40–50% RH and when atmospheric MH ranges from 100 to 200 m. Future remote sensing sensors such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) that have the capability to provide vertical distribution of aerosols will further enhance our ability to monitor and forecast air pollution. This study is among the first to examine the relationship between satellite and ground measurements over several global locations.