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Direct radiative forcing due to aerosols in Asia during March 2002
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a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
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Direct radiative forcing due to aerosols in Asia during March 2002 Soon-Ung Park a,⁎, Jaein I. Jeong b a Center for Atmospheric and Environmental Modeling, Seoul National University Research Park Rm 515, San 4-2 Bongcheon-dong Ganak-gu, Seoul, 151-818 Korea b School of Earth and Environmental Science, Seoul National University Seoul, 151-742, Korea
AR TIC LE D ATA
ABSTR ACT
Article history:
The Asian dust aerosol model (ADAM) and the aerosol dynamic model including the gas–
Received 5 February 2008
aerosol interaction processes together with the Column Radiation Model (CRM) of
Accepted 24 July 2008
Community Climate Model 3 and the output of the fifth generation of meso-scale model
Available online 19 September 2008
(MM5) in a grid 60 × 60 km2 in the Asian domain (70–150E, Equator-50N) have been employed to estimate direct radiative forcing of the Asian dust and the anthropogenic aerosols
Keywords:
including the BC, OC, secondary inorganic aerosol (SIA), mixed type aerosol (dust + BC + OC +
Aerosol direct radiative forcing
SIA) and sea salt aerosols at the surface, the top of atmosphere (TOA) and in the atmosphere
Air pollutant emission
for the period of 1–31 March 2002 during which a severe Asian dust event has been occurred
Asian dust aerosol
in the model domain. The results indicate that the ADAM model and the aerosol dynamic
Column Radiation Model (CRM)
model simulate quite well the spatial and temporal distributions of the mass concentration
Mixed type aerosol
of aerosols with the R2 value of more than 0.7. The estimated mean total column aerosol
Secondary inorganic aerosol
mass in the analysis domain for the whole period is found to be about 78 mg m− 2, of which 66% and 34% are, respectively, contributed by the Asian dust aerosol and all the other anthropogenic aerosols. However, the direct radiative forcing contributed by the Asian dust aerosol is about 22% of the mean radiative forcing at the surface (− 6.8 W m− 2), about 31% at the top of atmosphere (− 2.9 W m− 2) and about 13% in the atmosphere (3.8 W m− 2), suggesting relatively inefficient contribution of the Asian dust aerosol on the direct radiative forcing compared to the anthropogenic aerosols. The aerosol direct radiative forcing at the surface is mainly contributed by the mixed type aerosol (30%) and the SIA aerosol (25%) while at the top of atmosphere it is mainly contributed by the SIA aerosol (43%) and the Asian dust aerosol (31%) with positively (warming) contributed by BC and mixed type aerosols. The atmosphere is warmed mainly by the mixed type aerosol (55%) and the BC aerosol (26%). However, the largest radiative intensity of direct radiative forcing of aerosols is the BC aerosol. © 2008 Elsevier B.V. All rights reserved.
1.
Introduction
Atmospheric aerosols play major roles not only in atmospheric chemistry by providing reaction sites, serving as carriers for many condensed and sorbed species (Dentener et al., 1996; Zhang and Carmichael, 1999; Song and Carmichael, 2001; Jeong and Park, 2007) but also in the global climate
system by changing atmospheric radiation balance (Tegen and Fung, 1994; Andreae, 1996; Li et al., 1996; Tegen et al., 1996; Harrison et al., 2001; Chang and Park, 2004; Park et al., 2005; Satheesh and Moorthy, 2005; Jeong and Park, 2007). Aerosol particles are known to cool or warm the atmosphere directly by absorption, scattering and emission of solar and terrestrial radiation and indirectly by changing the albedo
⁎ Corresponding author. Tel./fax: +82 2 885 6715. E-mail address: [email protected] (S.-U. Park). 0048-9697/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2008.07.041
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and the life time of clouds by acting as cloud condensation nuclei (Charlson et al., 1992; Chang and Park, 2004). Current estimate of global mean radiative forcing due to anthropogenic aerosols is ranging from −0.4 to − 2.7 W m− 2 which is comparable to the present day greenhouse gases forcing of between 2.4 and 2.9 W m− 2 (IPCC, 2007). However, a large uncertainties due in part to the limited data on aerosol climatology and in part to the lack of our understanding on the processes responsible for the production, transport, physical and chemical evolution and removal of aerosols at various spatial and time scales make it impossible to correctly quantify the magnitude of radiative forcing. Asia, especially in China, is a major source of natural and anthropogenic aerosols over the Northern Hemisphere due to rapid economic expansion in many Asian countries and biomass burnings in South East Asia. Tropospheric aerosols that originate in Asia are the complex mixture of various aerosols such as wind-blown mineral dust from desert and semiarid regions in northern China and Mongolia and anthropogenic aerosols from a variety of sources. Asia dust (Hwangsa in Korean) which is a typical example of mineral aerosol frequently occurring in the Sand desert, Gobi desert and Loess plateau in northern China and Mongolia during the spring season (In and Park, 2003; Park and In, 2003; Park and Lee, 2004; Park et al., 2005) will experience acidic pollutants and anthropogenic aerosols emitted from the industrialized regions that are heavily concentrated in the eastern parts of China during long-range transport of dust. Consequently, a significant transformation of chemical composition of the dust is expected as indicated by observations (Saxena and Seigneur, 1983; Gao et al., 1991; Kang and Sang, 1991; Horai et al., 1993; Parungo et al., 1995; Carmichael et al., 1997; Kim and Park, 2001).
Fig. 1 – The model domain. The surface soil types ( shown.
○ Gobi,
395
Recently Chang and Park (2004) have developed an aerosol dynamic model and applied to estimate radiative forcing due to anthropogenic aerosols in East Asia during April 2001. They found that the mean direct shortwave radiative forcing at the surface and the top of atmosphere were about − 5.9 W m− 2 and −4.1 W m− 2 respectively with a slight warming of 1.8 W m− 2 in the atmosphere for the domain and time averaged column aerosol mass of 20 mg m− 2. However, this study does not include the effect of the Asian dust aerosol even though a severe Asian dust has occurred during the analysis period. This study has been expanded a little bit by including the direct radiative forcing of the Asian dust for the period of 19–23 March 2002 when a severe Asian dust occurred in the analysis domain (Park et al., 2005). For this case the temporal and spatial averaged column aerosol mass in East Asia was 880 mg m− 2, of which 98% of it (862.4 mg m− 2) was attributed to the Asian dust aerosol, and the rest of it (17.6 mg m− 2) to the anthropogenic aerosols for this analysis period. The estimated direct shortwave radiation due to the Asian dust aerosol was −6.7 W m− 2 at the surface and −3.3 W m− 2 at the top of the atmosphere, while that due to the anthropogenic aerosols was −4.3 W m− 2 at the surface and −2.7 W m− 2 at the top of atmosphere with the warming of 1.6 W m− 2 in the atmosphere, suggesting more effectiveness of the anthropogenic aerosols than the Asian dust on the direct radiative forcing. Even though, the direct radiative forcing of both the anthropogenic and Asian dust aerosols has been estimated by Park et al. (2005), interactions between gaseous pollutants and aerosols have not been taken into account for the transformation of aerosols during long-range transport. Jeong and Park (2007) have estimated the spatial and temporal aerosols concentration distribution in Asia during 1–31 March 2002. They found that the simulated gas-phase pollutants and
Sand,
Loess and
● Mixed) in the Asian dust source region are
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surface observation data with the land-use type and soil types in the Asian dust source regions. This model has been subsequently modified by Park and Lee (2004) by taking into account the concept of the minimally and fully dispensed parent soil particle size distribution (Shao et al., 2002). The detailed model description is given in Park and In (2003) and Park and Lee (2004).
2.3.
Fig. 2 – The average mineral components of soils in the Asian dust source regions. aerosols concentrations with the gas–aerosol interaction yield much better results in spatial and temporal concentration distributions than without the gas–aerosol interaction. The purpose of this study is to estimate the direct radiative forcing of both the Asian dust and the anthropogenic aerosols in Asia (70–150°E, Equator to 50°N) for the period of March 2002 with aerosol concentrations simulated by Jeong and Park (2007) using the gas–aerosol interaction process. The National Center for Atmospheric Research (NCAR) column radiation model (CRM) of the Community Climate Model (CCM3) with the simulated spectral mass concentration distribution by the Asian Dust Aerosol Model (ADAM) and the aerosol dynamic model (Chang and Park, 2004) has been used.
Aerosol dynamic model
An aerosol dynamic model developed by Chang and Park (2004) with the gas-phase chemistry of the California Institute of Technology (CIT, Russell et al., 1988) model and the aqueousphase chemistry of the Regional Acid Deposition Model (RADM, Walcek and Taylor, 1986; Chang et al., 1987) together with meteorological outputs of the MM5 model have been used to estimate anthropogenic aerosols and gaseous pollutants in Asia (Fig. 1). The size of anthropogenic and natural aerosols is divided into 12 bins for the size range of 0.01 μm to 77 μm in diameter. Six aerosol types including dust, black carbon (BC), organic carbon (OC), secondary inorganic aerosol (SIA), mixed type aerosol (Dust-SIA-BC-OC), and sea salt are treated in the model. The aerosol dynamic model includes such processes of nucleation, condensation/evaporation, coagulation, wet and dry deposition and hygroscopic growth. The more detailed model description is found in Chang and Park (2004), Park et al. (2005) and Jeong and Park (2007).
2.4.
Gas–aerosol interaction
The net removal of gas-phase species to a dust aerosol surface is described by the pseudo-first-order reaction that depends
2.
Model description
2.1.
Meteorological model
The meteorological model used in this study is the fifthgeneration mesoscale model of non-hydrostatic version (MM5, Pennsylvania State University/NCAR) in the x, y and σ coordinate (Grell et al., 1994; Dudhia et al., 1998). The cloudcooling scheme for convective parameterization, Blackadar scheme for the planetary boundary layer processes and the mixed phase of the moisture explicit scheme are used. The model domain is given in Fig. 1. The domain includes major dust source regions: the Sand, Loess, Gobi and mixed soil region (Park and In, 2003; Park and Lee, 2004). The model has a horizontal resolution of 60 km with 25 vertical layers. The simulation has been conducted for the period of 1 to 31 March 2002. The 6 hourly reanalyzed National Center for Environmental Program (NCEP) data are used for the initial and boundary conditions for the MM5 model. Hourly simulated meteorological variables obtained from the MM5 run are fed to the ADAM model and the aerosol dynamic model to get temporal and spatial distribution of aerosol concentrations in Asia.
2.2.
Asian Dust Aerosol Model (ADAM)
The ADAM model has been developed by Park and In (2003) using the statistical analysis of routinely reporting WMO
Fig. 3 – The refractive indices of mineral components in Asian dust source regions.
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on the number density of particles, radii of particles at each bin and the mass transfer coefficients of gas-phase species (i. e., N2O5, HNO3, NO2 and SO2) on the aerosol produces nitrate and sulfate by the heterogeneous reaction, but limited by the degree of acidity of the particle. If the equivalent cations concentrations of a soluble aerosol including NH+4, K+, Ca2+, − Mg2+ are higher than those of anions including SO2− 4 and NO3, gaseous N2O5, HNO3, NO2 and SO2 are stuck to the aerosol to form nitrate and sulfate on the aerosol until the acidity becomes to one. The sulfate and nitrate aerosols are allowed to be neutralized by the soluble cation in the dust particle. This neutralization scheme provides an overall constraint to mass of sulfate and nitrate accumulation on the mineral aerosol. The more detailed gas–aerosol interaction processes are given in Jeong and Park (2007).
2.5.
397
Radiation model
The CCM3 CRM model of NCAR (Kiehl et al., 1998; Briegleb, 1992) is used to estimate aerosol direct radiative forcing at the top of atmosphere (TOA) and the surface. This model uses a δ-Eddington approximation with 18 spectral intervals (seven for O3, one for the visible, seven for H2O and three for CO2) spanning the solar spectrum from 0.12 to 5 μm. Fig. 2 shows average mineral components of soils obtained from 37 soil samples in the Asian dust source regions of the Sand, Gobi, Loess and Mixed soil in northern China (Park, 2002). The refractive indices of these mineral components are shown in Fig. 3. The refractive index of quartz is obtained from high resolution transmission molecular absorption data base, that of calcite from Querry et al. (1978) and those of the other
Fig. 4 – Spatial distributions of (a) SO2, (b) NOx, (c) NH3, (d) VOC, (e) PM10 and (f) BC + OC emissions in a grid of 60 × 60 km2 (t gridcell− 1 month− 1) over the analysis domain (Streets et al., 2003).
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Fig. 5 – The time series of modeled and observed ( South Korea.
) (a) Total PM10, (b) PM10 and (c) Relative humidity (%) averaged over
major mineral components from Egan and Higeman (1979), Roush et al. (1991) and Querry (1987). The mineral components of amphibole, 14 Å clay and gypsum whose fractional composition ratio is less than 1% are neglected in calculating radiative forcing. The dust aerosols are assumed to be aggregated so that two effective medium theories of Bruggeman and Maxwell–Garnet (Bohren and Huffman, 1983; Cylek et al., 1988) are used to estimate the refractive indices.
3.
Gaseous pollutants and aerosol emissions
The emission data of SO2, NOx, NH3, CO, non-methane volatile organic carbon (NMVOC), Black carbon (BC), organic carbon (OC) and PM10 in the model domain are obtained from Streets et al. (2003) on the base year of 2000 (Fig. 4). The emission of NO and NO2 are, respectively, given by 90% and 10% of the total
Fig. 6 – A scatter plot of the monthly mean modeled versus observed (a) sulfate, (b) nitrate, (c) ammonium and (d) PM10 concentration in EANET sites with the optimal regression equations.
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Fig. 7 – Spatial distributions of monthly mean column concentrations of (a) Asian dust + PM10, (b) BC, (c) OC, (d) SIA, (e) Mixed type and (f) Total PM10 obtained from the model. The column concentration (μg m− 2) is expressed in common logarithm.
Fig. 8 – The same as in Fig. 7 except for the direct radiative forcing (W m− 2) at the surface.
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NOx emission in the whole domain. The emission of 6 lumped hydrocarbon species (HCHO, RCHO, OLE, ALK, ARO, C2H4) are calculated from total anthropogenic NMVOC divided by hydrocarbon splitting factor including isoprene that is classified as olefin. Fig. 4 shows spatial distributions of SO2, NOx, NMVOC, NH3, BC + OC, and PM10 emissions in a grid of 60 × 60 km2 for a month of March. The dominant source regions of most of pollutants are eastern China, south-eastern part of South Korea, and near Osaka and Tokyo in Japan. The main source regions of NH3 are located in the agricultural areas of central China and northeastern India with significant emissions of NMVOC and PM10 from biomass burning in South East Asia.
4.
Results
4.1.
Simulated model concentrations
The comparison of observed and modeled daily mean surface total PM10 concentration (Fig. 5a), anthropogenic and Asian dust of PM10 (Fig. 5b) and the relative humidity (Fig. 5c) averaged over South Korea for the period from 1 to 31 March 2002 is made and shown in Fig. 5. Hourly observed PM10 concentrations at 127 air pollution monitoring sites scattered over South Korea are used. The model results are obtained from grids of the first model layer (18 m above the ground) within the South Korean peninsula for comparison. The model simulates quite well the temporal variations of observed concentrations. The PM10 concentration during the Asian dust
period of 19 to 22 March 2002 is well simulated, suggesting the usefulness of the ADAM model for the simulation of Asian dust events. Most of mass of PM10 is mainly contributed by the Asian dust aerosol (Fig. 5b) while the contribution of anthropogenic aerosols to the total mass of PM10 is very small during the Asian dust period (Fig. 5b). The MM5 model simulates quite well the observed relative humidity over South Korea with the R2 value of 0.70 (Fig. 5c). The scatter plots of the model simulated monthly mean aerosols of sulfate, nitrate, ammonium and total PM10 concentration with the corresponding observed surface concentrations in the East Asia Network (EANET) are given in Fig. 6. The observed data in EANET are available for monthly mean values only (Jeong and Park, 2007). Fig. 6 indicates that the simulated sulfate, nitrate and PM10 concentrations show a good linear relationship with the corresponding observed ones with the R2 values over 0.7. However, the ammonium concentration shows a slightly poor relationship (R2 = 0.36) compared to other aerosols. The spatial distributions of monthly mean column integrated Asian dust plus emitted PM10, BC, OC, secondary inorganic aerosol (SIA), mixed type aerosol (dust + SIA + OC + BC) and total aerosol concentrations are given in Fig. 7. The total aerosol concentration (Fig. 7f) is largely contributed by the Asian dust in northern and eastern China and Mongolia and the PM10 emission from the biomass burning in South East Asia (Fig. 7a). Some of the aerosols in eastern China are contributed by the mixture of secondary inorganic aerosol (sulfate, nitrate and ammonium), mixed type aerosol and the Asian dust,
Fig. 9 – The same as in Fig. 8 except at the top of atmosphere (W m− 2).
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Fig. 10 – The same as in Fig. 8 except in the atmosphere (W m− 2).
while those in South East Asia are largely contributed by BC, OC and mixed type aerosols. The high total PM10 concentration over northern China and Mongolia is mainly due to the Asian dust aerosol whereas that in eastern China and the Yellow Sea is the mixture of the Asian dust and the anthropogenic aerosols. The large enhanced PM10 concentration extending from South East Asia to the Western Pacific Ocean (Fig. 7f) is due to the gas–aerosol interaction, where high emissions of SO2 and NOx over eastern China and NOx and VOC over South East Asia together with high relative humidity in these regions provide favorable conditions for the gas– aerosol interaction to form aerosols (Jeong and Park, 2007).
4.2.
Estimation of aerosol direct radiative forcing
The NCAR CRM (Kiehl et al., 1998; Briegleb, 1992) is used to estimate direct radiative forcing at the surface and the top of atmosphere (TOA) with the simulated Asian dust and the anthropogenic aerosol concentrations in Fig. 7. Vertical profiles of temperature, pressure, and H2O mixing ratio obtained from the MM5 simulation and those of ozone and CO2 mixing ratios from the CRM model are used as the initial profiles for CRM. The aerosol direct radiative forcing is obtained as the difference in shortwave net radiative fluxes at TOA and the surface between CRM simulations with and without aerosol mass loadings simulated by the aerosol dynamic model and ADAM. Fig. 8 shows the spatial distribution of mean direct radiative forcing at the surface (SRF) averaged for a month of March 2002 due to each type of aerosol (Figs. 8a–e) and total
sum of aerosol (Fig. 8f). The spatial distribution pattern of SRF (Fig. 8) follows that of the column integrated aerosol concentration in Fig. 7. However, SRF due to the Asian dust in northern China and Mongolia (Fig. 8a) is much weaker than other aerosols including SIA (Fig. 8d), mixed type aerosol (Fig. 8e) and BC (Fig. 8b). Consequently, the maximum SRF value region of more than − 20 W m− 2 extends northeastward from South East Asia to the East China Sea (Fig. 8f). Further northeastward extension of high SRF (N10 W m− 2) is mainly due to secondary inorganic aerosol (Fig. 8d) formed in the downstream of the high precursors emission regions. A much similar distribution pattern of the direct radiative forcing at the top of atmosphere (TOA) to that of SRF (Fig. 8) is seen in Fig. 9. The main difference is that the top of atmosphere is warmed by BC (Fig. 9b) and the mixed type aerosol (Fig. 9e) caused by the absorption of shortwave radiation by black carbon. However, the net direct radiative forcing at the top of atmosphere is cooling due to high concentrations of dust and PM10, OC and SIA. The maximum value of more than −7.5 W m− 2 of the net direct radiative forcing at TOA occurs in the region extending northeastward from South East Asia to Korea (Fig. 9f). The difference between the magnitude of the TOA radiative forcing (Fig. 9) and that of SRF (Fig. 8) allows to estimate the absorbed shortwave radiative flux in the atmosphere. The spatial distribution pattern of the atmospheric absorption flux (Fig. 10) quite resembles those of BC (Fig. 7a) and the mixed type aerosol (Fig. 7e) concentrations due to their absorptive radiative property. Some mineral dusts absorb shortwave radiation (Fig. 3), thereby contributing to the atmospheric
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Fig. 11 – The fractional contributions of each aerosol species to the time-area averaged (a) column integrated total aerosol mass concentration (mg m− 2), direct radiative forcing (b) at the surface (W m− 2), (c) at the top of atmosphere (W m− 2) and (d) in the atmosphere (W m− 2). The positive (+) and negative (−) contributions are indicated in (c).
absorption flux (Fig. 10a). The maximum atmospheric absorption of more than 15 W m− 2 occurs over South East Asia (Fig. 10f) where VOC, PM10 and OC + BC emissions are large (Fig. 4). The fractional contributions of each type of aerosols to the time-area averaged column integrated total mass, radiative forcings at the surface, at TOA and in the atmosphere averaged in the whole analysis domain in Fig. 1 for the period from 1 to 31 March 2002, are given in Fig. 11. The averaged total aerosol mass in Asia is about 78 mg m− 2, of which 66%, 14%, 11% and 7% are, respectively, contributed by Asian dust, the mixed type aerosol, SIA (sulfate, nitrate and ammonium) and sea salt (Fig. 11a). The contributions of OC (2%) and BC (0.2%) are small. The mean SRF is about −6.8 W m− 2, of which 30%, 25%, 22% and 13% are, respectively, contributed by the mixed type aerosol, SIA, Asian dust and BC (Fig. 11b), suggesting more effectiveness of the anthropogenic aerosol on the radiative forcing at the surface due to its small size distribution compared with that of the Asian dust aerosol (Park et al., 2005). The mean aerosol radiative forcing at TOA is about −2.9 W m− 2, of which 43%, 31% and 11% are, respectively, contributed by SIA, Asian dust and OC (Fig. 11c), also suggesting more effectiveness of the anthropogenic aerosol on the direct radiative forcing at TOA than the Asian dust aerosol. The difference between radiative forcing at TOA and at the surface yields to estimate the aerosol absorption in the atmosphere. The estimated mean radiative forcing due to atmospheric aerosol absorption in Asia is about 3.8 W m− 2, of which 55% and 26% are, respectively, contributed by the mixed type aerosol and BC (Fig. 11d). The contribution of the Asian dust aerosol is about 13% of the total aerosol radiative forcing in the atmosphere (Fig. 11d). Table 1 shows the radiative intensity of the direct radiative forcing of each aerosol at the surface, TOA and in the atmo-
sphere. The radiative intensity of radiative forcing is defined as the radiative forcing per unit mass concentration of each aerosol. All types of aerosols act to cool (negative forcing) the surface with the strongest radiative intensity of direct radiative forcing by the black carbon aerosol (−5.67 W mg− 1) and followed by the organic carbon (−0.31 W mg− 1), and SIA (− 0.20 W mg− 1). Even though the total mass concentration of the Asian dust aerosol (51.48 mg m− 2) is largest, the radiative intensity of the direct radiative forcing is smallest (−0.03 W mg− 1). The BC and the mixed type aerosols act to warm (positive forcing) the top of atmosphere with the radiative intensity of the direct radiative forcing of 1.35 W mg− 1 and 0.01 W mg− 1, respectively, whereas the other aerosols act to cool (negative forcing) the top of atmosphere. All species of aerosols act to warm (positive forcing) the atmosphere with the highest radiative intensity of the direct radiative forcing of the black carbon (6.21 W mg− 1), suggesting
Table 1 – The radiative intensity of the aerosol direct radiative forcing for various aerosols Aerosol
Asian dust SIA Mixed type BC OC Sea salt
Surface TOA Atmosphere Total (W mg− 1) (W mg− 1) (W mg− 1) mass con. (mg m− 2) −0.03 −0.20 −0.19 −5.67 −0.31 −0.04
−0.02 −0.18 +0.01 +1.35 −0.25 −0.04
0.01 0.01 0.19 6.21 0.07 0.00
51.48 8.58 10.92 0.16 1.56 5.46
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different roles of different species of aerosols on the direct radiative forcing.
2007) suggests the importance of this effect. This is now on hand.
5.
Acknowledgements
Conclusions
The ADAM and the aerosol dynamic model with the gas– aerosol interaction processes and the output of the MM5 meteorological model in a grid of 60 × 60 km2 in Asia (70–150E, Equator-50N) have been employed to simulate the temporal and spatial distribution of the Asian dust aerosol and the anthropogenic aerosol concentrations for the period of 1–31 March 2002, during which a severe Asian dust event has been observed. The simulated aerosols concentrations have been implemented to estimate direct radiative forcing of aerosols at the surface, the top of atmosphere (TOA) and in the atmosphere with the use of NCAR CRM of Community Climate Model 3 (CCM3). The results indicate that the area-time averaged column integrated total aerosol concentration in the analysis domain is found to be about 78 mg m− 2, of which 66%, 14%, 11%, 7%, 2% and 0.2% are, respectively, contributed by the Asian dust, the mixed-type, SIA, sea salt, OC and BC aerosols, implying more than 65% of the total aerosols being contributed by the Asian dust aerosol in this region. The area-time mean direct radiative forcing at the surface is found to be − 6.8 W m− 2, of which 30%, 25%, 22%, 13%, 7% and 3% are, respectively, contributed by the mixed-type, SIA, Asian dust, BC, OC and sea salt aerosols. These results indicate that the radiative intensity of the direct radiative forcing of the BC aerosol is the greatest (− 5.67 W mg− 1) at the surface while that of the Asian dust aerosol is the weakest (− 0.03 W mg− 1). The area-time averaged direct radiative forcing at the top of atmosphere is found to be −2.9 W m− 2, of which 43%, 31%, 11% and 6% are, respectively, negatively contributed by SIA, Asian dust, OC and sea salt aerosols, while 6% and 3% are, respectively, positively contributed by BC and the mixedtype aerosols. The radiative intensity of the direct radiative forcing of the BC aerosol is positively largest (1.35 W mg− 1) at the top of atmosphere while that of the OC aerosol is negatively largest (−0.25 W mg− 1), suggesting the differential contribution of different aerosol species. In the atmosphere all species of aerosols act to warm the atmosphere (3.8 W m− 2) with the largest radiative intensity of the BC aerosol (6.21 W mg− 1) and followed by the mixed aerosol (0.19 W mg− 1), and the OC aerosol (0.07 W mg− 1). This study clearly confirms the existance of a cooling effect (negative forcing) due to the direct effect of aerosol at the surface and TOA in Asia. However, the atmosphere of the troposphere above the ground is still warmed by the absorbing aerosol layer that consists of BC and the mixed type aerosol. This study mainly pertains to estimate the effects of the Asian dust aerosol and other anthropogenic aerosols produced by the gas–aerosol interaction on direct radiative forcings with the output of the MM5 meteorological model results. However, the feedback mechanism between the meteorological variables and the radiative forcing of aerosols is not considered in this study. A recent study (Ahn et al.,
This research is partially supported by Climate Environment System Research Center, The Academic research grant (2007) through Korea Meteorological Administration.
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Jeong J-I, Park S-U. Interaction of gaseous pollutants with aerosols in Asia during March 2002. Sci Total Environ 2007. doi:10.1016/j. scitotenv.2007.11.026. Kang KH, Sang SE. Influence of yellow sand on TSP in Seoul. Proceeding of the Second IUAPPA Regional Conference on Air Pollution. vol. II, Seoul, Korea, September 4–6; 1991. p. 65–70. Kiehl JT, Hack JJ, Bonan GB, Boville BA, Williamson DL, Rasch PJ. The national center for atmospheric research community climate model: CCM3. J Climate 1998;11:1131–49. Kim B-G, Park S-U. Transport and evolution of a winter-time yellow sand observed in Korea. Atmos Environ 2001;35:3191–201. Li X, Maring H, Savoie D, Voss K, Prospero JM. Dominance of mineral dust in aerosol light-scattering in the North-Atlantic trade wind. Nature 1996;380:416–9. Park S-U. Field survey of Yellow Sand source regions. Proceedings of the Workshop of Asian dust, 22 March 2002. Korea: Korea meteorological Administration; 2002. Park S-U, In H-J. Parameterization of dust emission for the simulation of the Yellow Sand (Asian dust) event observed in March 2002 in Korea. J Geophys Res 2003;108. doi:10.1029/ 2003JD003484. Park S-U, Lee E-H. Parameterization of Asian dust (Hwangsa) particle-size distributions for use in dust emission models. Atmos Environ 2004;38:2155–62. Park S-U, Chang L-S, Lee E-H. Direct radiative forcing due to aerosols in East Asia during a Hwangsa (Asian dust) event observed on 19–23 March 2002 in Korea. Atmos Environ 2005;38:2593–606. Parungo F, Kim Y, Zhu CJ, Harris J, Schnell R, Li XS, et al. Asian dust storms and their effects on radiation and climate, STC Rep. 2906. Hampton, Va: Sci. and Tech. Corp.; 1995. Querry MR. Optical constants of minerals and other materials from the millimeter to the UV. Report RDECCR-88009, US Army, Aberdeen, MD; 1987.
Querry MR, Osborne G, Lies K, Jordon R, Coveney RM. Complex refractive index of limestone in the visible and infrared. Appl Opt 1978;17:353–6. Roush T, Pollack J, Orenberg J. Derivation of wind infrared optical constants of some silicates and palagonite. Icarus 1991;9. Russell A, McCue KF, Cass GR. Mathematical Modeling of the formation of Nitrogen-containing air pollutants. 1. Evaluation of an Eulerian photochemical model. Environ Sci Technol 1988;22:263–71. Satheesh SK, Moorthy KK. Radiative effects of natural aerosols: a review. Atmos Environ 2005;39:2089–110. Saxena P, Seigneur C. Modeling of multiphase atmospheric aerosol. Atmos Environ 1983;17:1315–29. Shao Y, Jung E, Leslie LM. Numerical prediction of northeast Asian dust storms using an integrated wind erosion modeling system. J Geophys Res 2002;107:4814. doi:10.1029/ 2001JD001493. Song CH, Carmichael GR. A three-dimensional modeling investigation of the evolution processes of dust and sea-salt particles in East Asia. J Geophys Res 2001;106:18,131–54. Streets DG, Bond TC, Carmichael GR, Fernandes SD, Fu Q, He D, et al. An inventory of gaseous and primary aerosol emissions in Asia in the year 2000. J Geophys Res 2003;108. doi:10.1029/ 2002JD003093. Tegen I, Fung I. Modeling of mineral dust in the atmosphere: Sources, transport and optical thickness. J Geophys Res 1994;99:22897–914. Tegen I, Lacis AA, Fung I. The influence on climate forcing of mineral aerosols from disturbed soils. Nature 1996;380:419–22. Walcek CJ, Taylor GR. A theoretical method for computing vertical distributions of acidity and sulfate production within cumulus clouds. J Atmos Sci 1986;43:339–55. Zhang Y, Carmichael GR. The role of mineral aerosol in tropospheric chemistry in East Asia — a model study. J Appl Meteorol 1999;38:353–66.
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / s c i t o t e n v
Direct radiative forcing due to aerosols in Asia during March 2002 Soon-Ung Park a,⁎, Jaein I. Jeong b a Center for Atmospheric and Environmental Modeling, Seoul National University Research Park Rm 515, San 4-2 Bongcheon-dong Ganak-gu, Seoul, 151-818 Korea b School of Earth and Environmental Science, Seoul National University Seoul, 151-742, Korea
AR TIC LE D ATA
ABSTR ACT
Article history:
The Asian dust aerosol model (ADAM) and the aerosol dynamic model including the gas–
Received 5 February 2008
aerosol interaction processes together with the Column Radiation Model (CRM) of
Accepted 24 July 2008
Community Climate Model 3 and the output of the fifth generation of meso-scale model
Available online 19 September 2008
(MM5) in a grid 60 × 60 km2 in the Asian domain (70–150E, Equator-50N) have been employed to estimate direct radiative forcing of the Asian dust and the anthropogenic aerosols
Keywords:
including the BC, OC, secondary inorganic aerosol (SIA), mixed type aerosol (dust + BC + OC +
Aerosol direct radiative forcing
SIA) and sea salt aerosols at the surface, the top of atmosphere (TOA) and in the atmosphere
Air pollutant emission
for the period of 1–31 March 2002 during which a severe Asian dust event has been occurred
Asian dust aerosol
in the model domain. The results indicate that the ADAM model and the aerosol dynamic
Column Radiation Model (CRM)
model simulate quite well the spatial and temporal distributions of the mass concentration
Mixed type aerosol
of aerosols with the R2 value of more than 0.7. The estimated mean total column aerosol
Secondary inorganic aerosol
mass in the analysis domain for the whole period is found to be about 78 mg m− 2, of which 66% and 34% are, respectively, contributed by the Asian dust aerosol and all the other anthropogenic aerosols. However, the direct radiative forcing contributed by the Asian dust aerosol is about 22% of the mean radiative forcing at the surface (− 6.8 W m− 2), about 31% at the top of atmosphere (− 2.9 W m− 2) and about 13% in the atmosphere (3.8 W m− 2), suggesting relatively inefficient contribution of the Asian dust aerosol on the direct radiative forcing compared to the anthropogenic aerosols. The aerosol direct radiative forcing at the surface is mainly contributed by the mixed type aerosol (30%) and the SIA aerosol (25%) while at the top of atmosphere it is mainly contributed by the SIA aerosol (43%) and the Asian dust aerosol (31%) with positively (warming) contributed by BC and mixed type aerosols. The atmosphere is warmed mainly by the mixed type aerosol (55%) and the BC aerosol (26%). However, the largest radiative intensity of direct radiative forcing of aerosols is the BC aerosol. © 2008 Elsevier B.V. All rights reserved.
1.
Introduction
Atmospheric aerosols play major roles not only in atmospheric chemistry by providing reaction sites, serving as carriers for many condensed and sorbed species (Dentener et al., 1996; Zhang and Carmichael, 1999; Song and Carmichael, 2001; Jeong and Park, 2007) but also in the global climate
system by changing atmospheric radiation balance (Tegen and Fung, 1994; Andreae, 1996; Li et al., 1996; Tegen et al., 1996; Harrison et al., 2001; Chang and Park, 2004; Park et al., 2005; Satheesh and Moorthy, 2005; Jeong and Park, 2007). Aerosol particles are known to cool or warm the atmosphere directly by absorption, scattering and emission of solar and terrestrial radiation and indirectly by changing the albedo
⁎ Corresponding author. Tel./fax: +82 2 885 6715. E-mail address: [email protected] (S.-U. Park). 0048-9697/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2008.07.041
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and the life time of clouds by acting as cloud condensation nuclei (Charlson et al., 1992; Chang and Park, 2004). Current estimate of global mean radiative forcing due to anthropogenic aerosols is ranging from −0.4 to − 2.7 W m− 2 which is comparable to the present day greenhouse gases forcing of between 2.4 and 2.9 W m− 2 (IPCC, 2007). However, a large uncertainties due in part to the limited data on aerosol climatology and in part to the lack of our understanding on the processes responsible for the production, transport, physical and chemical evolution and removal of aerosols at various spatial and time scales make it impossible to correctly quantify the magnitude of radiative forcing. Asia, especially in China, is a major source of natural and anthropogenic aerosols over the Northern Hemisphere due to rapid economic expansion in many Asian countries and biomass burnings in South East Asia. Tropospheric aerosols that originate in Asia are the complex mixture of various aerosols such as wind-blown mineral dust from desert and semiarid regions in northern China and Mongolia and anthropogenic aerosols from a variety of sources. Asia dust (Hwangsa in Korean) which is a typical example of mineral aerosol frequently occurring in the Sand desert, Gobi desert and Loess plateau in northern China and Mongolia during the spring season (In and Park, 2003; Park and In, 2003; Park and Lee, 2004; Park et al., 2005) will experience acidic pollutants and anthropogenic aerosols emitted from the industrialized regions that are heavily concentrated in the eastern parts of China during long-range transport of dust. Consequently, a significant transformation of chemical composition of the dust is expected as indicated by observations (Saxena and Seigneur, 1983; Gao et al., 1991; Kang and Sang, 1991; Horai et al., 1993; Parungo et al., 1995; Carmichael et al., 1997; Kim and Park, 2001).
Fig. 1 – The model domain. The surface soil types ( shown.
○ Gobi,
395
Recently Chang and Park (2004) have developed an aerosol dynamic model and applied to estimate radiative forcing due to anthropogenic aerosols in East Asia during April 2001. They found that the mean direct shortwave radiative forcing at the surface and the top of atmosphere were about − 5.9 W m− 2 and −4.1 W m− 2 respectively with a slight warming of 1.8 W m− 2 in the atmosphere for the domain and time averaged column aerosol mass of 20 mg m− 2. However, this study does not include the effect of the Asian dust aerosol even though a severe Asian dust has occurred during the analysis period. This study has been expanded a little bit by including the direct radiative forcing of the Asian dust for the period of 19–23 March 2002 when a severe Asian dust occurred in the analysis domain (Park et al., 2005). For this case the temporal and spatial averaged column aerosol mass in East Asia was 880 mg m− 2, of which 98% of it (862.4 mg m− 2) was attributed to the Asian dust aerosol, and the rest of it (17.6 mg m− 2) to the anthropogenic aerosols for this analysis period. The estimated direct shortwave radiation due to the Asian dust aerosol was −6.7 W m− 2 at the surface and −3.3 W m− 2 at the top of the atmosphere, while that due to the anthropogenic aerosols was −4.3 W m− 2 at the surface and −2.7 W m− 2 at the top of atmosphere with the warming of 1.6 W m− 2 in the atmosphere, suggesting more effectiveness of the anthropogenic aerosols than the Asian dust on the direct radiative forcing. Even though, the direct radiative forcing of both the anthropogenic and Asian dust aerosols has been estimated by Park et al. (2005), interactions between gaseous pollutants and aerosols have not been taken into account for the transformation of aerosols during long-range transport. Jeong and Park (2007) have estimated the spatial and temporal aerosols concentration distribution in Asia during 1–31 March 2002. They found that the simulated gas-phase pollutants and
Sand,
Loess and
● Mixed) in the Asian dust source region are
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surface observation data with the land-use type and soil types in the Asian dust source regions. This model has been subsequently modified by Park and Lee (2004) by taking into account the concept of the minimally and fully dispensed parent soil particle size distribution (Shao et al., 2002). The detailed model description is given in Park and In (2003) and Park and Lee (2004).
2.3.
Fig. 2 – The average mineral components of soils in the Asian dust source regions. aerosols concentrations with the gas–aerosol interaction yield much better results in spatial and temporal concentration distributions than without the gas–aerosol interaction. The purpose of this study is to estimate the direct radiative forcing of both the Asian dust and the anthropogenic aerosols in Asia (70–150°E, Equator to 50°N) for the period of March 2002 with aerosol concentrations simulated by Jeong and Park (2007) using the gas–aerosol interaction process. The National Center for Atmospheric Research (NCAR) column radiation model (CRM) of the Community Climate Model (CCM3) with the simulated spectral mass concentration distribution by the Asian Dust Aerosol Model (ADAM) and the aerosol dynamic model (Chang and Park, 2004) has been used.
Aerosol dynamic model
An aerosol dynamic model developed by Chang and Park (2004) with the gas-phase chemistry of the California Institute of Technology (CIT, Russell et al., 1988) model and the aqueousphase chemistry of the Regional Acid Deposition Model (RADM, Walcek and Taylor, 1986; Chang et al., 1987) together with meteorological outputs of the MM5 model have been used to estimate anthropogenic aerosols and gaseous pollutants in Asia (Fig. 1). The size of anthropogenic and natural aerosols is divided into 12 bins for the size range of 0.01 μm to 77 μm in diameter. Six aerosol types including dust, black carbon (BC), organic carbon (OC), secondary inorganic aerosol (SIA), mixed type aerosol (Dust-SIA-BC-OC), and sea salt are treated in the model. The aerosol dynamic model includes such processes of nucleation, condensation/evaporation, coagulation, wet and dry deposition and hygroscopic growth. The more detailed model description is found in Chang and Park (2004), Park et al. (2005) and Jeong and Park (2007).
2.4.
Gas–aerosol interaction
The net removal of gas-phase species to a dust aerosol surface is described by the pseudo-first-order reaction that depends
2.
Model description
2.1.
Meteorological model
The meteorological model used in this study is the fifthgeneration mesoscale model of non-hydrostatic version (MM5, Pennsylvania State University/NCAR) in the x, y and σ coordinate (Grell et al., 1994; Dudhia et al., 1998). The cloudcooling scheme for convective parameterization, Blackadar scheme for the planetary boundary layer processes and the mixed phase of the moisture explicit scheme are used. The model domain is given in Fig. 1. The domain includes major dust source regions: the Sand, Loess, Gobi and mixed soil region (Park and In, 2003; Park and Lee, 2004). The model has a horizontal resolution of 60 km with 25 vertical layers. The simulation has been conducted for the period of 1 to 31 March 2002. The 6 hourly reanalyzed National Center for Environmental Program (NCEP) data are used for the initial and boundary conditions for the MM5 model. Hourly simulated meteorological variables obtained from the MM5 run are fed to the ADAM model and the aerosol dynamic model to get temporal and spatial distribution of aerosol concentrations in Asia.
2.2.
Asian Dust Aerosol Model (ADAM)
The ADAM model has been developed by Park and In (2003) using the statistical analysis of routinely reporting WMO
Fig. 3 – The refractive indices of mineral components in Asian dust source regions.
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on the number density of particles, radii of particles at each bin and the mass transfer coefficients of gas-phase species (i. e., N2O5, HNO3, NO2 and SO2) on the aerosol produces nitrate and sulfate by the heterogeneous reaction, but limited by the degree of acidity of the particle. If the equivalent cations concentrations of a soluble aerosol including NH+4, K+, Ca2+, − Mg2+ are higher than those of anions including SO2− 4 and NO3, gaseous N2O5, HNO3, NO2 and SO2 are stuck to the aerosol to form nitrate and sulfate on the aerosol until the acidity becomes to one. The sulfate and nitrate aerosols are allowed to be neutralized by the soluble cation in the dust particle. This neutralization scheme provides an overall constraint to mass of sulfate and nitrate accumulation on the mineral aerosol. The more detailed gas–aerosol interaction processes are given in Jeong and Park (2007).
2.5.
397
Radiation model
The CCM3 CRM model of NCAR (Kiehl et al., 1998; Briegleb, 1992) is used to estimate aerosol direct radiative forcing at the top of atmosphere (TOA) and the surface. This model uses a δ-Eddington approximation with 18 spectral intervals (seven for O3, one for the visible, seven for H2O and three for CO2) spanning the solar spectrum from 0.12 to 5 μm. Fig. 2 shows average mineral components of soils obtained from 37 soil samples in the Asian dust source regions of the Sand, Gobi, Loess and Mixed soil in northern China (Park, 2002). The refractive indices of these mineral components are shown in Fig. 3. The refractive index of quartz is obtained from high resolution transmission molecular absorption data base, that of calcite from Querry et al. (1978) and those of the other
Fig. 4 – Spatial distributions of (a) SO2, (b) NOx, (c) NH3, (d) VOC, (e) PM10 and (f) BC + OC emissions in a grid of 60 × 60 km2 (t gridcell− 1 month− 1) over the analysis domain (Streets et al., 2003).
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Fig. 5 – The time series of modeled and observed ( South Korea.
) (a) Total PM10, (b) PM10 and (c) Relative humidity (%) averaged over
major mineral components from Egan and Higeman (1979), Roush et al. (1991) and Querry (1987). The mineral components of amphibole, 14 Å clay and gypsum whose fractional composition ratio is less than 1% are neglected in calculating radiative forcing. The dust aerosols are assumed to be aggregated so that two effective medium theories of Bruggeman and Maxwell–Garnet (Bohren and Huffman, 1983; Cylek et al., 1988) are used to estimate the refractive indices.
3.
Gaseous pollutants and aerosol emissions
The emission data of SO2, NOx, NH3, CO, non-methane volatile organic carbon (NMVOC), Black carbon (BC), organic carbon (OC) and PM10 in the model domain are obtained from Streets et al. (2003) on the base year of 2000 (Fig. 4). The emission of NO and NO2 are, respectively, given by 90% and 10% of the total
Fig. 6 – A scatter plot of the monthly mean modeled versus observed (a) sulfate, (b) nitrate, (c) ammonium and (d) PM10 concentration in EANET sites with the optimal regression equations.
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399
Fig. 7 – Spatial distributions of monthly mean column concentrations of (a) Asian dust + PM10, (b) BC, (c) OC, (d) SIA, (e) Mixed type and (f) Total PM10 obtained from the model. The column concentration (μg m− 2) is expressed in common logarithm.
Fig. 8 – The same as in Fig. 7 except for the direct radiative forcing (W m− 2) at the surface.
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NOx emission in the whole domain. The emission of 6 lumped hydrocarbon species (HCHO, RCHO, OLE, ALK, ARO, C2H4) are calculated from total anthropogenic NMVOC divided by hydrocarbon splitting factor including isoprene that is classified as olefin. Fig. 4 shows spatial distributions of SO2, NOx, NMVOC, NH3, BC + OC, and PM10 emissions in a grid of 60 × 60 km2 for a month of March. The dominant source regions of most of pollutants are eastern China, south-eastern part of South Korea, and near Osaka and Tokyo in Japan. The main source regions of NH3 are located in the agricultural areas of central China and northeastern India with significant emissions of NMVOC and PM10 from biomass burning in South East Asia.
4.
Results
4.1.
Simulated model concentrations
The comparison of observed and modeled daily mean surface total PM10 concentration (Fig. 5a), anthropogenic and Asian dust of PM10 (Fig. 5b) and the relative humidity (Fig. 5c) averaged over South Korea for the period from 1 to 31 March 2002 is made and shown in Fig. 5. Hourly observed PM10 concentrations at 127 air pollution monitoring sites scattered over South Korea are used. The model results are obtained from grids of the first model layer (18 m above the ground) within the South Korean peninsula for comparison. The model simulates quite well the temporal variations of observed concentrations. The PM10 concentration during the Asian dust
period of 19 to 22 March 2002 is well simulated, suggesting the usefulness of the ADAM model for the simulation of Asian dust events. Most of mass of PM10 is mainly contributed by the Asian dust aerosol (Fig. 5b) while the contribution of anthropogenic aerosols to the total mass of PM10 is very small during the Asian dust period (Fig. 5b). The MM5 model simulates quite well the observed relative humidity over South Korea with the R2 value of 0.70 (Fig. 5c). The scatter plots of the model simulated monthly mean aerosols of sulfate, nitrate, ammonium and total PM10 concentration with the corresponding observed surface concentrations in the East Asia Network (EANET) are given in Fig. 6. The observed data in EANET are available for monthly mean values only (Jeong and Park, 2007). Fig. 6 indicates that the simulated sulfate, nitrate and PM10 concentrations show a good linear relationship with the corresponding observed ones with the R2 values over 0.7. However, the ammonium concentration shows a slightly poor relationship (R2 = 0.36) compared to other aerosols. The spatial distributions of monthly mean column integrated Asian dust plus emitted PM10, BC, OC, secondary inorganic aerosol (SIA), mixed type aerosol (dust + SIA + OC + BC) and total aerosol concentrations are given in Fig. 7. The total aerosol concentration (Fig. 7f) is largely contributed by the Asian dust in northern and eastern China and Mongolia and the PM10 emission from the biomass burning in South East Asia (Fig. 7a). Some of the aerosols in eastern China are contributed by the mixture of secondary inorganic aerosol (sulfate, nitrate and ammonium), mixed type aerosol and the Asian dust,
Fig. 9 – The same as in Fig. 8 except at the top of atmosphere (W m− 2).
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Fig. 10 – The same as in Fig. 8 except in the atmosphere (W m− 2).
while those in South East Asia are largely contributed by BC, OC and mixed type aerosols. The high total PM10 concentration over northern China and Mongolia is mainly due to the Asian dust aerosol whereas that in eastern China and the Yellow Sea is the mixture of the Asian dust and the anthropogenic aerosols. The large enhanced PM10 concentration extending from South East Asia to the Western Pacific Ocean (Fig. 7f) is due to the gas–aerosol interaction, where high emissions of SO2 and NOx over eastern China and NOx and VOC over South East Asia together with high relative humidity in these regions provide favorable conditions for the gas– aerosol interaction to form aerosols (Jeong and Park, 2007).
4.2.
Estimation of aerosol direct radiative forcing
The NCAR CRM (Kiehl et al., 1998; Briegleb, 1992) is used to estimate direct radiative forcing at the surface and the top of atmosphere (TOA) with the simulated Asian dust and the anthropogenic aerosol concentrations in Fig. 7. Vertical profiles of temperature, pressure, and H2O mixing ratio obtained from the MM5 simulation and those of ozone and CO2 mixing ratios from the CRM model are used as the initial profiles for CRM. The aerosol direct radiative forcing is obtained as the difference in shortwave net radiative fluxes at TOA and the surface between CRM simulations with and without aerosol mass loadings simulated by the aerosol dynamic model and ADAM. Fig. 8 shows the spatial distribution of mean direct radiative forcing at the surface (SRF) averaged for a month of March 2002 due to each type of aerosol (Figs. 8a–e) and total
sum of aerosol (Fig. 8f). The spatial distribution pattern of SRF (Fig. 8) follows that of the column integrated aerosol concentration in Fig. 7. However, SRF due to the Asian dust in northern China and Mongolia (Fig. 8a) is much weaker than other aerosols including SIA (Fig. 8d), mixed type aerosol (Fig. 8e) and BC (Fig. 8b). Consequently, the maximum SRF value region of more than − 20 W m− 2 extends northeastward from South East Asia to the East China Sea (Fig. 8f). Further northeastward extension of high SRF (N10 W m− 2) is mainly due to secondary inorganic aerosol (Fig. 8d) formed in the downstream of the high precursors emission regions. A much similar distribution pattern of the direct radiative forcing at the top of atmosphere (TOA) to that of SRF (Fig. 8) is seen in Fig. 9. The main difference is that the top of atmosphere is warmed by BC (Fig. 9b) and the mixed type aerosol (Fig. 9e) caused by the absorption of shortwave radiation by black carbon. However, the net direct radiative forcing at the top of atmosphere is cooling due to high concentrations of dust and PM10, OC and SIA. The maximum value of more than −7.5 W m− 2 of the net direct radiative forcing at TOA occurs in the region extending northeastward from South East Asia to Korea (Fig. 9f). The difference between the magnitude of the TOA radiative forcing (Fig. 9) and that of SRF (Fig. 8) allows to estimate the absorbed shortwave radiative flux in the atmosphere. The spatial distribution pattern of the atmospheric absorption flux (Fig. 10) quite resembles those of BC (Fig. 7a) and the mixed type aerosol (Fig. 7e) concentrations due to their absorptive radiative property. Some mineral dusts absorb shortwave radiation (Fig. 3), thereby contributing to the atmospheric
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Fig. 11 – The fractional contributions of each aerosol species to the time-area averaged (a) column integrated total aerosol mass concentration (mg m− 2), direct radiative forcing (b) at the surface (W m− 2), (c) at the top of atmosphere (W m− 2) and (d) in the atmosphere (W m− 2). The positive (+) and negative (−) contributions are indicated in (c).
absorption flux (Fig. 10a). The maximum atmospheric absorption of more than 15 W m− 2 occurs over South East Asia (Fig. 10f) where VOC, PM10 and OC + BC emissions are large (Fig. 4). The fractional contributions of each type of aerosols to the time-area averaged column integrated total mass, radiative forcings at the surface, at TOA and in the atmosphere averaged in the whole analysis domain in Fig. 1 for the period from 1 to 31 March 2002, are given in Fig. 11. The averaged total aerosol mass in Asia is about 78 mg m− 2, of which 66%, 14%, 11% and 7% are, respectively, contributed by Asian dust, the mixed type aerosol, SIA (sulfate, nitrate and ammonium) and sea salt (Fig. 11a). The contributions of OC (2%) and BC (0.2%) are small. The mean SRF is about −6.8 W m− 2, of which 30%, 25%, 22% and 13% are, respectively, contributed by the mixed type aerosol, SIA, Asian dust and BC (Fig. 11b), suggesting more effectiveness of the anthropogenic aerosol on the radiative forcing at the surface due to its small size distribution compared with that of the Asian dust aerosol (Park et al., 2005). The mean aerosol radiative forcing at TOA is about −2.9 W m− 2, of which 43%, 31% and 11% are, respectively, contributed by SIA, Asian dust and OC (Fig. 11c), also suggesting more effectiveness of the anthropogenic aerosol on the direct radiative forcing at TOA than the Asian dust aerosol. The difference between radiative forcing at TOA and at the surface yields to estimate the aerosol absorption in the atmosphere. The estimated mean radiative forcing due to atmospheric aerosol absorption in Asia is about 3.8 W m− 2, of which 55% and 26% are, respectively, contributed by the mixed type aerosol and BC (Fig. 11d). The contribution of the Asian dust aerosol is about 13% of the total aerosol radiative forcing in the atmosphere (Fig. 11d). Table 1 shows the radiative intensity of the direct radiative forcing of each aerosol at the surface, TOA and in the atmo-
sphere. The radiative intensity of radiative forcing is defined as the radiative forcing per unit mass concentration of each aerosol. All types of aerosols act to cool (negative forcing) the surface with the strongest radiative intensity of direct radiative forcing by the black carbon aerosol (−5.67 W mg− 1) and followed by the organic carbon (−0.31 W mg− 1), and SIA (− 0.20 W mg− 1). Even though the total mass concentration of the Asian dust aerosol (51.48 mg m− 2) is largest, the radiative intensity of the direct radiative forcing is smallest (−0.03 W mg− 1). The BC and the mixed type aerosols act to warm (positive forcing) the top of atmosphere with the radiative intensity of the direct radiative forcing of 1.35 W mg− 1 and 0.01 W mg− 1, respectively, whereas the other aerosols act to cool (negative forcing) the top of atmosphere. All species of aerosols act to warm (positive forcing) the atmosphere with the highest radiative intensity of the direct radiative forcing of the black carbon (6.21 W mg− 1), suggesting
Table 1 – The radiative intensity of the aerosol direct radiative forcing for various aerosols Aerosol
Asian dust SIA Mixed type BC OC Sea salt
Surface TOA Atmosphere Total (W mg− 1) (W mg− 1) (W mg− 1) mass con. (mg m− 2) −0.03 −0.20 −0.19 −5.67 −0.31 −0.04
−0.02 −0.18 +0.01 +1.35 −0.25 −0.04
0.01 0.01 0.19 6.21 0.07 0.00
51.48 8.58 10.92 0.16 1.56 5.46
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different roles of different species of aerosols on the direct radiative forcing.
2007) suggests the importance of this effect. This is now on hand.
5.
Acknowledgements
Conclusions
The ADAM and the aerosol dynamic model with the gas– aerosol interaction processes and the output of the MM5 meteorological model in a grid of 60 × 60 km2 in Asia (70–150E, Equator-50N) have been employed to simulate the temporal and spatial distribution of the Asian dust aerosol and the anthropogenic aerosol concentrations for the period of 1–31 March 2002, during which a severe Asian dust event has been observed. The simulated aerosols concentrations have been implemented to estimate direct radiative forcing of aerosols at the surface, the top of atmosphere (TOA) and in the atmosphere with the use of NCAR CRM of Community Climate Model 3 (CCM3). The results indicate that the area-time averaged column integrated total aerosol concentration in the analysis domain is found to be about 78 mg m− 2, of which 66%, 14%, 11%, 7%, 2% and 0.2% are, respectively, contributed by the Asian dust, the mixed-type, SIA, sea salt, OC and BC aerosols, implying more than 65% of the total aerosols being contributed by the Asian dust aerosol in this region. The area-time mean direct radiative forcing at the surface is found to be − 6.8 W m− 2, of which 30%, 25%, 22%, 13%, 7% and 3% are, respectively, contributed by the mixed-type, SIA, Asian dust, BC, OC and sea salt aerosols. These results indicate that the radiative intensity of the direct radiative forcing of the BC aerosol is the greatest (− 5.67 W mg− 1) at the surface while that of the Asian dust aerosol is the weakest (− 0.03 W mg− 1). The area-time averaged direct radiative forcing at the top of atmosphere is found to be −2.9 W m− 2, of which 43%, 31%, 11% and 6% are, respectively, negatively contributed by SIA, Asian dust, OC and sea salt aerosols, while 6% and 3% are, respectively, positively contributed by BC and the mixedtype aerosols. The radiative intensity of the direct radiative forcing of the BC aerosol is positively largest (1.35 W mg− 1) at the top of atmosphere while that of the OC aerosol is negatively largest (−0.25 W mg− 1), suggesting the differential contribution of different aerosol species. In the atmosphere all species of aerosols act to warm the atmosphere (3.8 W m− 2) with the largest radiative intensity of the BC aerosol (6.21 W mg− 1) and followed by the mixed aerosol (0.19 W mg− 1), and the OC aerosol (0.07 W mg− 1). This study clearly confirms the existance of a cooling effect (negative forcing) due to the direct effect of aerosol at the surface and TOA in Asia. However, the atmosphere of the troposphere above the ground is still warmed by the absorbing aerosol layer that consists of BC and the mixed type aerosol. This study mainly pertains to estimate the effects of the Asian dust aerosol and other anthropogenic aerosols produced by the gas–aerosol interaction on direct radiative forcings with the output of the MM5 meteorological model results. However, the feedback mechanism between the meteorological variables and the radiative forcing of aerosols is not considered in this study. A recent study (Ahn et al.,
This research is partially supported by Climate Environment System Research Center, The Academic research grant (2007) through Korea Meteorological Administration.
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