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11.
A dust deflation module was developed and coupled with the air quality modeling system RAMS-CMAQ to simultaneously treat all the major tropospheric aerosols（i.e.,organic and black carbons,sulfate,nitrate, ammonia,soil dust,and sea salt）.Then the coupled system was applied to East Asia to simulate Asian dust aerosol generation,transport and dry/wet removal processes during 14-25 March 2002 when two strong dust storms occurred consecutively.To evaluate model performance and to analyze the observed features of dust aerosols over the East Asian region,model results were compared to concentrations of suspended particulate matter of 10μm or less(PM10;1-h intervals) at four remote Japanese stations and daily air pollution index （API） values for PM10 at four large Chinese cities.The modeled values were generally in good agreement with observed data,and the model reasonably reproduced two dust storm outbreaks and generally predicted the dust onset and cessation times at each observation site.In addition,hourly averaged values of aerosol optical thickness（AOT） were calculated and compared with observations at four Aerosol Robotic Network （AERONET） stations to assess the model’s capability of estimating dust aerosol column burden.Analysis shows that modeled and observed AOT values were generally comparable and that the contribution of dust aerosols to AOT was significant only with regard to their source regions and their transport paths. 相似文献
12.
Ricardo M. Llamas Roberto Bonifaz Mauro Valdés David Riveros-Rosas Amando LeyvaContreras 《Geofísica Internacional》2013,52(4):321-341
The purpose of this paper was to study aerosol particles in the Northwestern region of Mexico (NWM) through Aerosol Optical Thickness (AOT) parameter in the atmosphere. This parameter represents one of the extinction coefficients of solar radiation and the rate of suspended particles in the atmosphere. For determination of AOT, we considered the use of remote sensors outside of the atmosphere. In particular, Moderate Resolution Imaging Spectroradiometer (MODIS) which can measure the atmospheric AOT thickness. Data from the MODIS sensor must be validated before they are considered reliable. For this task, we required surface measurements to obtain a correlation with the data acquired with the remote radiometer. The paper describes the validation process performed for data obtained with MODIS through measurements provided by an AErosol RObotic NETwork (AERONET) photometer located in the city of Hermosillo, Sonora, NWM. Additionally, we carried out a temporal analysis based on the behavior of the AOT graphics and spatial analysis supported in maps with sufficient information. 相似文献
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Various algorithms have recently been developed in order to retrieve the aerosol optical thickness (AOT) at continental scales. However, they are, to some extent, subject to large uncertainties resulting from some necessary physical assumptions on land surface anisotropy and level of brightness. In fact, disentangling aerosol and surface signals contained in the top of atmosphere (TOA) radiance received at the satellite level are a matter of difficulty because a single sensor itself cannot gather all required spatial, temporal, spectral and angular information. In particular, each instrument yields limited scanning configuration due to its platform's orbital characteristics. In this regard, a synergetic approach is presented which merges Advanced Along-Track Scanning Radiometer (AATSR) TOA radiances and the MODerate resolution Imaging Spectroradiometer (MODIS) Bi-directional Reflectance Distribution Function (BRDF)/Albedo Model Parameters Product for the retrieval of AOT at 0.55, 0.66, and 0.87 µm wavelengths over non-Lambertian land surface at a 5 km spatial resolution. In this approach, BRDF products serve to assess the surface reflectance in the AATSR geometry as a boundary layer. The peculiarity of the approach is that no specific assumption is required about the spectral characteristics of land surface, thus allowing for a quantitative retrieval of aerosol particles over any arbitrary land unit in virtue of combining forward and nadir AATSR observations. We obtain on average differences within 0.1τ compared to in situ AErosol RObotic NETwork (AERONET) measurements and 36 retrievals corresponding to 27 January, 12 February, 16 March, 28 May, 26 June, and 21 July 2006, respectively, over the city of Beijing in China. Pearson's correlation coefficient is 0.94 and 0.96 for nadir and forward AATSR, respectively. These suggest that AOT retrieval over land is indeed feasible by taking benefit of the validated MODIS BRDF. Besides, the first results indicate that the AATSR retrievals might be used to evaluate the spectral behaviour of the AOT. 相似文献
15.
大气校正是高光谱图像定量反演地表参数的前提。为充分利用高光谱数据本身的光谱特点,提出了一种协同反演大气气溶胶光学厚度(aerosol optical thickness,AOT)与水汽含量(water vapor content,WV)的大气校正方法,在同时考虑了气溶胶模式、AOT和WV这3个因素的综合影响基础上,采用循环迭代的思想,基于6S辐射传输模型,反演大气参数及地表反射率,弥补了现有反演算法中没有同时考虑AOT与WV的不足;并以武汉市Hyperion高光谱图像为例,验证了该算法的有效性。从与FLAASH算法及MOIDS提供的AOT和WV产品对比来看,该算法能较好地校正气溶胶与水汽对高光谱图像的影响,且反演过程中所有的输入均来自图像数据本身或6S辐射传输模型,无需输入额外的参数。 相似文献
16.
Martin Saliba Raymond Ellul Liberato Camilleri Hans Güsten 《Journal of Atmospheric Chemistry》2008,60(2):117-135
A 10-year study of surface ozone mixing ratios in the Central Mediterranean was conducted based on continuous ozone measurements
from 1997 to 2006 by a background regional Global Atmospheric Watch (GAW) station on the island of Gozo. The mean annual maximum
mixing ratio is of the order of 66 ppbv in April–May with a broad secondary maximum of 64 ppbv in July–September. No long-term
increase or decrease in the background level of surface ozone could be observed over the last 10 years. This is contrary to
observations made in the Eastern Mediterranean, where a slow decrease in the background ozone mixing ratio was observed over
the past 7 years. Despite the very high average annual ozone mixing ratio exceeding 50 ppbv—in fact, the highest average background
ozone mixing ratio ever measured in Europe—, the diurnal O
3 max/O
3 min index of <1.40 indicates that the island of Gozo is a good site for measuring background surface ozone. However, frequent
photosmog events from June to September during the past 10 years with ozone mixing ratios exceeding 90 ppbv indicate that
the Central Mediterranean is prone to long-range transport of air pollutants from Europe by northerly winds. This was particularly
evident during the so-called “August heatwave” of the year 2003 when the overall ozone mixing ratio was 4.6 ppbv higher than
the average of all other 9 months of August since 1997. Air mass back-trajectory analysis of the August 2003 photosmog episodes
on Gozo confirmed that ozone pollution originated from the European continent. Regression analysis was used to analyse the
10-year data set in order to model the behaviour of the ozone mixing ratio in terms of the meteorological parameters of wind
speed, relative humidity, global radiation, temperature, month of year, wind sector, atmospheric pressure, and time of day
(predictors). Most of these predictors were found to significantly affect the ozone mixing ratios. From March to November,
the monthly average of the AOT40 threshold value for the protection of crops and vegetation against ozone was constantly exceeded
on Gozo during the past 10 years. 相似文献
17.
Sachin D. Ghude S. L. Jain B. C. Arya G. Beig Y. N. Ahammed Arun Kumar B. Tyagi 《Journal of Atmospheric Chemistry》2008,60(3):237-252
Seven year data of hourly surface ozone concentration is analyzed to study diurnal cycle, trends, excess of ozone levels above
threshold value and cumulative ozone exposure indices at a tropical megacity, Delhi. The ozone levels clearly exhibit a diurnal
cycle, similar to what has been found in other urban places. A sharp increase in the ozone levels during forenoon and a sharp
decrease in the early afternoon can be observed. The average rate of increase in ozone concentration between 09 and 12 h has
been observed to be 7.1 ppb h−1. We find that the daily maximum and daytime 8-h (10–17 h) ozone levels are increasing at a rate of about 1.7 (± 0.7) and
1.3 (± 0.56) ppb y−1, respectively. The directives on ozone pollution in ambient air provided by United Nations Economic Commission for Europe
and World Health Organization for vegetation (AOT40) and human health protection were used to assess the air quality. The
present surface ozone levels in the city are high enough to exceed “Critical Levels” which are considered to be safe for human
health, vegetation and forest. The human health threshold was exceeded for up to ~45 days per year. The AOT40 (Accumulated
exposure Over a Threshold of 40 ppb) threshold was exceeded significantly during winter (D-J-F) and pre-monsoon (M-A-M) (Rabi
crop growing season) season in India. Translating AOT40 exceedances during pre-monsoon into relative yield loss we estimate
yield loss of 22.7%, 22.5%, 16.3% and 5.5% for wheat, cotton, soybean and rice, respectively. 相似文献
18.
Modelling of near-surface ozone over South Asia 总被引：2，自引：1，他引：1
Magnuz Engardt 《Journal of Atmospheric Chemistry》2008,59(1):61-80
Hourly, three-dimensional, fields of tropospheric ozone have been produced for 12 consecutive months on a domain covering
South Asia, using the regional Eulerian off-line chemistry transport model MATCH. The results were compared with background
observations to investigate diurnal and seasonal variations of near-surface ozone in the region. MATCH reproduced the seasonality
of near-surface ozone at most locations in the area. However, the current, and previous, studies indicate that the model consequently
overestimate night-time concentrations, while it occasionally underestimates the day-time, near-surface, ozone concentrations.
The lowest monthly-mean concentrations of near-surface ozone are typically experienced in June–September, coincident with
the rainy season in most areas. The seasonality is not identical across the domain; some locations have a completely different
trend. Large areas in Northern India and Nepal show a secondary minimum during the cold winter season (December–January).
High concentrations of near-surface ozone are found over the oceans, close to the Indian subcontinent, due to the less efficient
dry deposition to water surfaces; over parts of Tibet due to influence of free tropospheric air and little deposition to snow
covered surfaces; and along the Gangetic valley due to the large emissions of precursors in this region. Monthly-mean ozone
concentrations in the densely populated northern India range from 30–45 ppb(v). The model results were also used to produce maps of AOT40. The results point towards similar levels of AOT40 in India as
in Europe: large areas of India show 3-month AOT40 values above 3 ppm(v) hours.
相似文献
| Magnuz EngardtEmail: |