According to the authors,
"The atmospheric aerosols could thus disturb solar radiation income and global climate through influencing the transfer of energy in the atmosphere in two ways (Hansen et al. 1997, Carslaw et al. 2013). On the one hand, the atmospheric aerosols can directly reflect and absorb the solar radiation in both the troposphere and stratosphere. On the other hand, the atmospheric aerosols could modify the optical properties of clouds through cloud condensation nuclei which lead to increase cloud droplet number concentrations, and thus affect the incoming radiation indirectly"
"The atmospheric aerosols play a dominant role in the global energy balance by contributing to a net reduction of 5 to 10% in solar energy received at the Earth's surface, therefore the dynamics of the atmospheric aerosol load is of vital importance for the science and policy of environmental pollution and global climate change"
A 5-10% decrease in solar energy received at the Earth's surface due to aerosols is huge [up to 136 W/m2], and far more than the ~0.5 W/m2 increase alleged due to man-made greenhouse gases since the beginning of the industrial revolution. A mere 1-2% change in global albedo from clouds/aerosols is sufficient to tip the balance between global warming or cooling.
"Our understanding of the global aerosol change is rather limited, although it is well known that aerosol forcing could affect the global radiative budget, hydrological processes, carbon, nitrogen and sulfur cycles, as well as climate change."Although aerosol emissions have been sharply curtailed and continue to decline in industrialized countries, little to no regulation is in place in developing countries, thus the authors find
"It is interesting to find that high concentrations of aerosols are mainly distributed in regions where developing countries are located (Asia and Africa), and an increasing trend could also be observed."
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| Global trend shown in top graph, followed by land and ocean. |
Global aerosol change in the last decade: An analysis based on MODIS data
- DOI: 10.1016/j.atmosenv.2014.04.053
- Under a Creative Commons license
Open Access
Highlights
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- Global aerosol change in different regions in the last decade.
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- Which year is the highest or lowest of aerosols in different regions.
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- Where are the aerosols decreasing or increasing.
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- The aerosol changes with seasons in northern and southern hemisphere.
Abstract
Abstract
Our understanding of the global aerosol change is rather limited, although it is well known that aerosol forcing could affect the global radiative budget, hydrological processes, carbon, nitrogen and sulfur cycles, as well as climate change. To understand the wide range effects of aerosols, it is key to obtain aerosol characteristics at high spatio-temporal resolutions. In this study, we try to map the global variations of the aerosol optical depth (AOD) using two aerosol products retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) satellite instrument. It is found that the global average AOD is 0.126 over the last decade (2003 – 2012). The highest and the lowest AOD occurred in 2007 and 2010, respectively. AOD variations between land and ocean, north and south hemispheres, among seven continents and four oceans were also explored. It is interesting to find that high concentrations of aerosols are mainly distributed in regions where developing countries are located (Asia and Africa), and an increasing trend could also be observed. Seasonal variations of AOD (air quality) can also be noted, which is decreasing in the north hemisphere from spring, summer to autumn and winter, but increasing in the south hemisphere.
Keywords
- globe;
- aerosol;
- air quality;
- climate change
1. Introduction
In recent years, especially in developing country, air pollution is getting worse. Aerosols are an important component of haze. The diameters of aerosol particles in Earth’s atmosphere range from 0.1 to 1.0 micron, which are coincident with the sunlight wavelength. The atmospheric aerosols could thus disturb solar radiation income and global climate through influencing the transfer of energy in the atmosphere in two ways (Hansen et al. 1997, Carslaw et al. 2013). On the one hand, the atmospheric aerosols can directly reflect and absorb the solar radiation in both the troposphere and stratosphere. On the other hand, the atmospheric aerosols could modify the optical properties of clouds through cloud condensation nuclei which lead to increase cloud droplet number concentrations, and thus affect the incoming radiation indirectly (Gao et al. 2000; Wang et al. 2009). The atmospheric aerosols play a dominant role in the global energy balance by contributing to a net reduction of 5 to 10% in solar energy received at the Earth's surface, therefore the dynamics of the atmospheric aerosol load is of vital importance for the science and policy of environmental pollution and global climate change (Fuzzi et al. 2006).
However, our understanding of the global aerosol change is rather limited, because it is difficult to assess the profile of atmospheric aerosols at a global scale (Hess et al. 1998). Traditionally, ground-based observation stations have been established to measure the concentration of aerosols, which are mainly located in densely populated areas. In addition, the lifetimes of most aerosols are short and therefore their geographical distribution is highly variable and strongly related to their sources. Thus the observations tend to be biased by local/regional industrial activities, vehicle transport, land surface cover and soil type, and climatological condition. In recent years, satellite instruments have been used to estimate indirectly the spatial distribution of aerosol optical depth. AVHRR (Advanced Very High Resolution Radiometer) is the first satellite instrument used to estimate the global-mean AOD (Husar et al. 1997; Kaufman et al. 2002, Zhao et al. 2008). However, the accuracy of aerosol estimates over land area assessed by AVHRR data need to be improved, because the limited band number cannot fully capture the radiative properties of land surface which are highly variable (Robert et al. 2009, Hsu et al. 2012). MODIS (Moderate Resolution Imaging Spectrometer) is a 36-band Earth Observing System (EOS) instrument onboard the National Aeronautics and Space Administration’s (NASA) satellites. It could provide accurate daily insight into the global distribution of aerosols because of its global coverage, radiometric resolution and dynamic ranges, and accurate calibration in the visible and infrared regions of the spectrum bands designed for retrievals of atmospheric properties (King et al. 1996). Moreover, MODIS aerosol products can provide consistent evaluation over land and ocean surfaces because we use the same instrument MODIS, and there is relatively better comparability because the measurement error is similar for different time and place (Ichoku et al. 2004). These observations have been widely used in the research of climate change (Yu et al., 2006) and to monitor atmosphere environment (Chu et al. 2003, Al-Saadi et al. 2005, Wang et al. 2010, de Meij et al. 2012, Kim et al. 2014).
In recent year, pollution (haze) is very serious, especially in developing country. Spatio-temporal variation and trends in atmospheric aerosols as well as their impact on solar radiation and clouds are crucial for regional and global environment (air quality) assessment. The purpose of this paper is to use MODIS aerosol product to analysis the spatio-temporal characteristics of aerosol at global and regional scale, which help people know our environment (the distribution of pollution) in recent years. So People and government take appropriate measures to protect our environment.
Pollution is definitely a problem factor for countries which is rising. Carbon content is rising. Now all of this has to be stopped or steps must be taken to reduce the dilemma.
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