Changes In Aerosol Optical Properties Research Articles

Integrating satellite and model data to explore spatial-temporal changes in aerosol optical properties and their meteorological relationships in northwest India

This study aims to analyze the temporal and spatial distribution of Aerosol Optical Properties across Northwest India using aerosol data from MODIS (Moderate Resolution Imaging Spectroradiometer) and OMI (Ozone Monitoring Instrument) sensors from 2003 to 2022. Therefore, this study investigated the decadal, interannual, and seasonal changes in aerosol optical properties, vegetation index, and meteorological parameters in the northwest Indian region (8 boxes). Using GIOVANNI (Goddard Earth Sciences Data and Information Services Center (GES DISC) Online Visualization and Analysis Infrastructure), we retrieved daily and monthly Aqua and Terra MODIS products of aerosol optical depth (AOD), Angstrom exponent (AE), normalized difference vegetation index (NDVI), and OMI aerosol index (AI) to examine the spatiotemporal variations by using statistical approaches. The results demonstrated that the decadal averages of aerosol properties showed values of AOD 0.35 (Aqua) and 0.34 (Terra) and AE 1.20 (Aqua) and 1.10 (Terra) with the highest levels during the post-monsoon. Notably, the mean interannual concentrations of AOD and NDVI consistently surpass 0.3, and AE and AI exceed 1 in most locations, underscoring the persistence of high aerosol loading. Also, the study revealed a negative decadal change in AOD of about −8.24 %, while AE, AI, and NDVI showed positive decadal changes of about 9.24 %, 15.09 %, and 12.67 %, respectively. In addition, aerosol optical properties and local meteorology strongly correlated (−0.8 to +0.8). Principal Component Analysis (PCA) identifies meteorological parameters as significant drivers, with the first three components explaining over 70 % of the variation in aerosol optical properties. The NOAA HYSPLIT trajectory model suggests that the long-distance dust transport from the Arabian Peninsula frequently penetrates Gujarat province and then to northwest India. The results contributed to air quality management strategies and provided valuable insights into regional climate and air quality with the influence of meteorology.

Sensitivity of formaldehyde (HCHO) column measurements from a geostationary satellite to temporal variation of the air mass factor in East Asia

Abstract. We examine upcoming geostationary satellite observations of formaldehyde (HCHO) vertical column densities (VCDs) in East Asia and the retrieval sensitivity to the temporal variation of air mass factors (AMFs) considering the presence of aerosols. Observation system simulation experiments (OSSE) were conducted using a combination of a global 3-D chemical transport model (GEOS-Chem), a radiative transfer model (VLIDORT), and a HCHO retrieval algorithm developed for the Geostationary Environment Monitoring Spectrometer (GEMS), which will be launched in 2019. Application of the retrieval algorithm to simulated hourly radiances yields the retrieved HCHO VCDs, which are then compared with the GEOS-Chem HCHO VCDs as true values for the evaluation of the retrieval algorithm. In order to examine the retrieval sensitivity to the temporal variation of AMF, we examine three AMF specifications, AMFm, AMFh, and AMFmh, using monthly, hourly, and monthly mean hourly input data for their calculation, respectively. We compare the retrieved HCHO VCDs using those three AMFs and find that the HCHO VCDs with AMFh are in better agreement with the true values than the results using AMFmh and AMFm. AMFmh reflects diurnal variation of planetary boundary layer and other meteorological parameters, so that the results with AMFmh show a better performance than those with AMFm. The differences between AMFh and AMFm range from −0.76 to 0.74 in absolute value and are mainly caused by temporal changes in aerosol chemical compositions and aerosol vertical distributions, which result in −27 to 58 and −34 to 43 % changes in HCHO VCDs over China, respectively, compared to HCHO VCDs using AMFm. We apply our calculated AMF table together with OMI aerosol optical properties to OMI HCHO products in March 2006, when Asian dust storms occurred, and find −32 to 47 % changes in the retrieved HCHO columns due to temporal changes in aerosol optical properties in East Asia. The impact of aerosol temporal variability cannot be neglected for future geostationary observations.

Changes in aerosol optical properties due to dust storms in the Middle East and Southwest Asia

Super dust storms occurred over the Middle East and southwest Asia on March 2012. These storms reduced the air quality over the Gulf Region, Iraq, Iran, and Pakistan. Airports were shut down due to poor visibility, schools were closed, and hundreds of people were hospitalized with respiratory problems. In order to better understand the effects of such dust storms we have analyzed aerosol optical and radiative properties during this event using data from the Moderate Resolution Imaging Spectroradiometer and the Aerosol Robotic Network. Maximum aerosol optical depth (AOD) values occurred on the18th of March in Kuwait, Bahrain, Qatar, and Saudi Arabia, where values of 4.9, 4.4, 4.3, and 4.9 were recorded, respectively. In Oman, the Arabian Sea, and Iran, maximum AOD values occurred on the 19th of March, reaching 4.5, 5, and 5, respectively. The dust storm then spread across Pakistan, passing through Multan, Faisalabad, and Lahore where maximum AOD values of 2.1, 2.6, and 2.7, respectively, were attained on the 20th of March. The maximum aerosol volume size distributions (VSDs) in Lahore occurred on dusty days and minimum VSDs on non-dusty days. The VSD, single scattering albedo, refractive index, and asymmetry parameter values on dusty days suggested that dust aerosols were predominant over anthropogenic aerosols in these urban environments. The shortwave aerosol radiative forcing (ARF) values (on both dusty and non-dusty days) ranged between −50Wm−2 and −194Wm−2 (average: −114±40Wm−2) at the earth's surface, and between −31Wm−2 and −105Wm−2 (average: −58±25Wm−2) at the top of the atmosphere (TOA). The longwave aerosol ARF values ranged between +6Wm−2 and +20Wm−2 (average: +12±4Wm−2) at the earth's surface, and between +7Wm−2 and +30Wm−2 (average: +16±7Wm−2) at the TOA. Longwave radiations therefore produced significant warming, both at the TOA and at the earth's surface.

Aerosol impact on the brightening in Japan

The long‐term changes in aerosol optical depth (AOD) and single scattering albedo (SSA) at 0.75 μm from the 1970s to the 2000s at 14 sites in Japan were estimated from the direct and diffuse irradiances measured by ground‐based broadband radiometers under clear‐sky conditions. Noticeable changes in AOD and SSA were seen: AOD decreased by 0.02, and SSA increased by 0.21. The ratio of surface solar irradiance to solar irradiance at the top of the atmosphere under clear‐sky conditions, calculated from the estimated AOD and SSA, showed apparent brightening of +0.05, of which +0.01 was attributed to a decrease of AOD and +0.04 to an increase of SSA. The cloud forcing of the surface solar irradiance, estimated as the difference between the surface solar irradiance measured under cloudy‐sky conditions and that under clear‐sky conditions, showed no significant trend. These findings suggest that the brightening in Japan has been caused by changes in aerosol optical properties, especially SSA, rather than by cloud changes.

Characterization of a volcanic ash episode in southern Finland caused by the Grimsvötn eruption in Iceland in May 2011

Abstract. The volcanic eruption of Grimsvötn in Iceland in May 2011 affected surface-layer air quality at several locations in Northern Europe. In Helsinki, Finland, the main pollution episode lasted for more than 8 h around the noon of 25 May. We characterized this episode by relying on detailed physical, chemical and optical aerosol measurements. The analysis was aided by air mass trajectory calculations, satellite measurements, and dispersion model simulations. During the episode, volcanic ash particles were present at sizes from less than 0.5 μm up to sizes >10 μm. The mass mean diameter of ash particles was a few μm in the Helsinki area, and the ash enhanced PM10 mass concentrations up to several tens of μg m−3. Individual particle analysis showed that some ash particles appeared almost non-reacted during the atmospheric transportation, while most of them were mixed with sea salt or other type of particulate matter. Also sulfate of volcanic origin appeared to have been transported to our measurement site, but its contribution to the aerosol mass was minor due the separation of ash-particle and sulfur dioxide plumes shortly after the eruption. The volcanic material had very little effect on PM1 mass concentrations or sub-micron particle number size distributions in the Helsinki area. The aerosol scattering coefficient was increased and visibility was slightly decreased during the episode, but in general changes in aerosol optical properties due to volcanic aerosols seem to be difficult to be distinguished from those induced by other pollutants present in a continental boundary layer. The case investigated here demonstrates clearly the power of combining surface aerosol measurements, dispersion model simulations and satellite measurements in analyzing surface air pollution episodes caused by volcanic eruptions. None of these three approaches alone would be sufficient to forecast, or even to unambiguously identify, such episodes.

Wildfire particulate matter in Europe during summer 2003: meso-scale modeling of smoke emissions, transport and radiative effects

Abstract. The present study investigates effects of wildfire emissions on air quality in Europe during an intense fire season that occurred in summer 2003. A meso-scale chemistry transport model CHIMERE is used, together with ground based and satellite aerosol optical measurements, to assess the dispersion of fire emissions and to quantify the associated radiative effects. The model has been improved to take into account a MODIS-derived daily smoke emission inventory as well as the injection altitude of smoke particles. The simulated aerosol optical properties are put into a radiative transfer model to estimate (off-line) the effects of smoke particles on photolysis rates and atmospheric radiative forcing. We have found that the simulated wildfires generated comparable amounts of primary aerosol pollutants (130 kTons of PM2.5, fine particles) to anthropogenic sources during August 2003, and caused significant changes in aerosol optical properties not only close to the fire source regions, but also over a large part of Europe as a result of the long-range transport of the smoke. Including these emissions into the model significantly improved its performance in simulating observed aerosol concentrations and optical properties. Quantitative comparison with MODIS and POLDER data during the major fire event (3–8 August 2003) showed the ability of the model to reproduce high aerosol optical thickness (AOT) over Northern Europe caused by the advection of the smoke plume from the Portugal source region. Although there was a fairly good spatial agreement with satellite data (correlation coefficients ranging from 0.4 to 0.9), the temporal variability of AOT data at specific AERONET locations was not well captured by the model. Statistical analyses of model-simulated AOT data at AERONET ground stations showed a significant decrease in the model biases suggesting that wildfire emissions are responsible for a 30% enhancement in mean AOT values during the heat-wave episode. The implications for air quality over a large part of Europe are significant during this episode. First, directly, the modeled wildfire emissions caused an increase in average PM2.5 ground concentrations from 20 to 200%. The largest enhancement in PM2.5 concentrations stayed, however, confined within a 200 km area around the fire source locations and reached up to 40 μg/m³. Second, indirectly, the presence of elevated smoke layers over Europe significantly altered atmospheric radiative properties: the model results imply a 10 to 30% decrease in photolysis rates and an increase in atmospheric radiative forcing of 10–35 W m−2 during the period of strong fire influence throughout a large part of Europe. These results suggest that sporadic wildfire events may have significant effects on regional photochemistry and atmospheric stability, and need to be considered in current chemistry-transport models.