Abstract
Abstract. Small aerosols are mostly anthropogenic, and the fine-mode aerosol optical depth (fAOD) can be used to infer anthropogenic aerosol amounts. We estimate AOD and fAOD globally on a monthly time scale from 2001 to 2010 by integrating monthly satellite-based (MODIS and MISR) and ground-based (AERONET) observations. For fAOD, three integration methods are developed to utilize global coverage by satellite data and maximize the influence of AERONET data. We evaluate each method by applying the method without a few randomly-chosen AERONET data and comparing its output with the few AERONET data. The best method of the three is based on integrating the Ångström exponent (AE) data from MODIS, MISR and AERONET, and its output is closer to AERONET fAOD accuracy than MODIS or MISR fAOD over both ocean and land. Using our integrated data, we find that the global 2001–2010 average of 500 nm AOD and fAOD is 0.17 and 0.089, respectively. Eastern China as a region shows the largest decadal-mean fAOD. The linear trend of global AOD or global fAOD from 2001 to 2010 is found to be slightly negative. This decreasing trend is particularly pronounced over the West (Western Europe and US/Canada combined) where AOD and fAOD reductions are about −20%. By contrast, fAOD in India and eastern China combined increased slightly. These results reflect the overall anthropogenic aerosol emission reduction in the West, and stagnating conditions in Asia. Moreover, our results in the West are consistent with the so-called surface brightening phenomenon in the recent decades.
Highlights
The importance of small particles is amplified, when human health is an issue. Dockery et al (1993) showed a strongSolar radiation reaching the Earth’s surface decreased in many regions of the world from the 1950’s to the 1980’s relationship particulates, baentdweSecnhwmaorrtztalaiStnydoaNlniddeasaEir(a2p0ro0tl0hlu)tiroenpowrtietdh fine that
The present study is a significant expansion of Chung et al (2005), in that (a) we bring in Multi-angle Imaging Spectroradiometer (MISR) data as well, (b) more importantly we address fine-mode AOD (fAOD) as well as aerosol optical depth (AOD), and (c) we look at the trend of global and region mean AOD and fAOD as well as the climatology
Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) fAOD is defined as the ratio of black carbon, organic aerosol and sulfate AODs combined to total AOD. (ii) The spatial pattern in the MISR + Moderate Resolution Imaging Spectroradiometer (MODIS) + GOCART fine-mode fraction (FMF) is coupled with the sparsely distributed AErosol RObotic NETwork (AERONET) FMFs, using Eq (2). (iii) If this FMF > 1.0 it is set to 1.0, and if the FMF < 0.0 it is set to 0.0. (iv) The FMF is multiplied by the integrated AOD estimate to obtain fAOD
Summary
The importance of small particles is amplified, when human health is an issue. Dockery et al (1993) showed a strong. This is the level 3.0 data that have been validated at Stage 3 (for AOD) and at Stage 2 (for fine and medium mode fractions) Out of this monthly product, we extracted AOD, fAOD, mAOD, and cAOD (see Table 1 for the acronyms). These parameters originally available on the 0.5◦ by 0.5◦ spatial resolution are converted into the T42 resolution using the median method that we adopted for the MODIS data processing in Sect. The global and decadal (2001–2010) mean MISR AOD at 550 nm shows a tiny difference (about 0.01) between the median and arithmetic average methods. We logarithmically interpolate AOD (or fAOD) to the desired wavelength
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