TOMS Aerosol Index Research Articles

Aerosol-ozone correlations during dust transport episodes

Abstract. Its location in the Mediterranean region and its physical characteristics render Mt. Cimone (44°11′ N, 10°42′ E), the highest peak of the Italian northern Apennines (2165 m asl), particularly suitable to study the transport of air masses from the north African desert area to Europe. During these northward transports 12 dust events were registered in measurements of the aerosol concentration at the station during the period June–December 2000, allowing the study of the impact of mineral dust transports on free tropospheric ozone concentrations, which were also measured at Mt. Cimone. Three-dimensional backward trajectories were used to determine the air mass origin, while TOMS Aerosol Index data for the Mt. Cimone area were used to confirm the presence of absorbing aerosol over the measurement site. A trajectory statistical analysis allowed identifying the main source areas of ozone and aerosols. The analysis of these back trajectories showed that central Europe and north and central Italy are the major pollution source areas for ozone and fine aerosol, whereas the north African desert regions were the most important source areas for coarse aerosol and low ozone concentrations. During dust events, the Mt. Cimone mean volume concentration for coarse particles was 6.18 µm3/cm3 compared to 0.63 µm3/cm3 in dust-free conditions, while the ozone concentrations were 4% to 21% lower than the monthly mean background values. Our observations show that surface ozone concentrations were lower than the background values in air masses coming from north Africa, and when these air masses were also rich in coarse particles, the lowest ozone values were registered. Moreover, preliminary results on the possible impact of the dust events on PM10 and ozone values measured in Italian urban and rural areas showed that during the greater number of the considered dust events, significant PM10 increases and ozone decreases have occurred in the Po valley.

Saharan dust episodes in Hungarian aerosol: elemental signatures and transport trajectories

In the present work the episodic appearance of Saharan dust in the Hungarian aerosol has been investigated using our 1991–2000 aerosol data obtained with proton-induced X-ray emission elemental analysis. For selecting local episodes of Saharan origin three different approximations have been applied. On the one hand, episodes have been selected in the time series of concentration ratios Ti/Ca, Si/Al, Al/Ca, Ti/Fe, Si/Fe, Ca/Fe generally accepted as regional signatures of Saharan dust. Remarkable similarity has been found between Italian and Hungarian observations of Saharan dust episodes in spring 1991. The tracing power of the regional signatures generally accepted as fingerprints of Saharan dust was found to be limited in the present region due to anthropogenic effects during transport. On the other hand, either backward air trajectories or TOMS aerosol index data from NASA satellites NIMBUS7 and EARTH PROBE have been used as additional tool for assigning local effects to Saharan sources. A nine-month overlap in the application of trajectories and TOMS maps permitted us to compare the applicability of these selection tools. During the period considered we assigned nearly 50 local episodes to Saharan sources. Data are presented for the frequency, the probable source areas and the seasonal distribution of Saharan episodes in the Hungarian atmosphere.

Sensitivity of TOMS aerosol index to boundary layer height: Implications for detection of mineral aerosol sources

The TOMS aerosol index (AI) is proposed as a powerful tool in determining the sources of mineral aerosols. The sensitivity of the AI to the height of the aerosol layer has been noted previously, but the implications of this sensitivity for deducing sources has not been explicitly considered. Here, we present a methodology and sensitivity test to show the importance of spatial and temporal variations of the planetary boundary layer height to deducing sources using the AI. These results suggest that while dry topographic low sources may be large sources of desert dust, conclusions eliminating other sources may be premature, especially when these sources occur on the edges of deserts, where boundary layer heights are lower, and human influences potentially more important. The compounding problem of differentiating downwind transport and local sources suggests it may not currently be possible to use the AI to conclusively determine mineral aerosol source regions.

Development of Aerosol Global scale Chemical Transport Model (AGCTM) and its application

A global scale chemical transport model for gaseous and aerosol species (AGCTM) has been developed to study possible effects of changes in human and natural emission activities on atmospheric environment and the Earth's environment. The AGCTM simulation as well as Lagrange particle simulation was performed for about 40 days from Feb. 21 to March 31, 2001 during TRACE-P field campaign. In the Lagrange particle simulation, emission areas for yellow sand and anthropogenic pollutant in China, Korea, Taiwan, and Japan were identified, and movements of the hypothetical non-buoyant particles released from the areas were kept tracked for one week. A technique to label particles with different colors for those released on different days allowed us to estimate spatial distribution of aged air-mass. In the AGCTM simulation, calculated results were compared with TRACE-P airborne observation, TOMS Aerosol Index, and surface observation in China.

Biomass burning in Asia: Annual and seasonal estimates and atmospheric emissions

Estimates of biomass burning in Asia are developed to facilitate the modeling of Asian and global air quality. A survey of national, regional, and international publications on biomass burning is conducted to yield consensus estimates of “typical” (i.e., non‐year‐specific) estimates of open burning (excluding biofuels). We conclude that 730 Tg of biomass are burned in a typical year from both anthropogenic and natural causes. Forest burning comprises 45% of the total, the burning of crop residues in the field comprises 34%, and 20% comes from the burning of grassland and savanna. China contributes 25% of the total, India 18%, Indonesia 13%, and Myanmar 8%. Regionally, forest burning in Southeast Asia dominates. National, annual totals are converted to daily and monthly estimates at 1° × 1° spatial resolution using distributions based on AVHRR fire counts for 1999–2000. Several adjustment schemes are applied to correct for the deficiencies of AVHRR data, including the use of moving averages, normalization, TOMS Aerosol Index, and masks for dust, clouds, landcover, and other fire sources. Good agreement between the national estimates of biomass burning and adjusted fire counts is obtained (R2= 0.71–0.78). Biomass burning amounts are converted to atmospheric emissions, yielding the following estimates: 0.37 Tg of SO2, 2.8 Tg of NOx, 1100 Tg of CO2, 67 Tg of CO, 3.1 Tg of CH4, 12 Tg of NMVOC, 0.45 Tg of BC, 3.3 Tg of OC, and 0.92 Tg of NH3. Uncertainties in the emission estimates, measured as 95% confidence intervals, range from a low of ±65% for CO2emissions in Japan to a high of ±700% for BC emissions in India.

Desert aerosol transport in the Mediterranean region as inferred from the TOMS aerosol index

We proposed to identify the sources of desert dust aerosols with local maxima of the TOMS aerosol index distribution averaged for the long period. Being simpler than the approach based on a dusty days occurrence, our method gives the same results. It was first shown that in spring‐summer, the flux of dust from the sources located at latitude ∼16°N and longitude ∼16°E and around latitude ∼19°N and longitude ∼6°W exceed the sinks due to settling and transport. As a result the atmosphere over North Africa is almost permanently loaded with a significant amount of mineral desert dust in spring and in summer. It is also shown that the Chad basin source located around latitude 16°N and longitude 16°E is relatively more stable with a maximum activity around April. The region around latitude 19°N and longitude 6°W appears as a more variable source with maximum in July. Low pressure systems, called Sharav cyclones, mobilize the already suspended mineral dust and transport it eastward and northward along the Mediterranean basin. A new method for description of dust plumes propagation was applied to the study of dust events in the Mediterranean Sea and enabled us to follow their dynamics. Identifiable dust plumes appear first in the western sector of the sea and then move eastward with a speed of about 7 to 8 degrees per day. In spring, this motion continues at least up to the eastern coast of the Mediterranean. In summer the dustplume is prevented from penetrating further east of about 15°E.

Surface Ozone Episode Due to Stratosphere-Troposphere Exchange and Free Troposphere-Boundary Layer Exchange in Busan During Asian Dust Events

The current paper reports on the enhancement of O<TEX>$_3$</TEX>, CO, NO<TEX>$_2$</TEX>, and aerosols during the Asian dust event that occurred over Korea on 1 May 1999. To confirm the origin and net flux of the O<TEX>$_3$</TEX>, CO, NO<TEX>$_2$</TEX>, and aerosols, the meteorological parameters of the weather conditions were investigated using Mesoscale Meteorological Model 5(MM5) and the TOMS total ozone and aerosol index, the back trajectory was identified using the Hybrid Single-Particle Lagrangian Integrated Trajectory Model(HYSPLIT), and the ozone and ozone precursor concentrations were determined using the Urban Ashed Model(UAM). In the presence of sufficiently large concentrations of NO<TEX>$\sub$</TEX>x/, the oxidation of CO led to O<TEX>$_3$</TEX> formation with OH, HO<TEX>$_2$</TEX>, NO, and NO<TEX>$_2$</TEX> acting as catalysts. The sudden enhancement of O<TEX>$_3$</TEX>, CO, NO<TEX>$_2$</TEX> and aerosols was also found to be associated with a deepening cut-off low connected with a surface cyclone and surface anticyclone located to the south of Korea during the Asian dust event. The wave pattern of the upper trough/cut-off low and total ozone level remained stationary when they came into contact with a surface cyclone during the Asian dust event. A typical example of a stratosphere-troposphere exchange(STE) of ozone was demonstrated by tropopause folding due to the jet stream. As such, the secondary maxima of ozone above 80 ppbv that occurred at night in Busan, Korea on 1 May 2001 were considered to result from vertical mixing and advection from a free troposphere-boundary layer exchange in connection with an STE in the upper troposphere. Whereas the sudden enhancement of ozone above 100 ppbv during the day was explained by the catalytic reaction of ozone precursors and transport of ozone from a slow-moving anticyclone area that included a high level of ozone and its precursors coming from China to the south of Korea. The aerosols identified in the free troposphere over Busan, Korea on 1 May 1999 originated from the Taklamakan and Gobi deserts across the Yellow River. In particular, the 1000m profile indicated that the source of the air parcels was from an anticyclone located to the south of Korea. The net flux due to the first invasion of ozone between 0000 LST and 0600 LST on 1 May 1999 agreed with the observed ground-based background concentration of ozone. From 0600 LST to 1200 LST, the net flux of the second invasion of ozone was twice as much as the day before. In this case, a change in the horizontal wind direction may have been responsible for the ozone increase.

Asian Dust Transport during Blocking Episode Days over Korea

Asian dust(or yellow sand) occurs mainly in spring and occasionally in winter in east Asia, when the weather conditions are under an upper trough/cut-off low and surface high/low pressure system during blocking episode days associated with the stationary patterns of the upper level jet stream. The transport mechanism for Asian dust during the blocking episode days in spring 2001 was analyzed using the TOMS aerosol index and meteorological mesoscale model 5(MM5). Based on the E vector, an extension of an Eliassen-Palm flux, the blocking episode days were found to be associated with the development of an upper cut-off low and surface cyclones. Concurrently, the occurrence of dust storms was also determined by strong cold advection at the rear of a jet streak, which exhibited a maximum wind speed within the upper jet stream. As such, the transport mechanism for Asian dust from China was due to advection of the isentropic potential vorticity(IPV) and isentropic surfaces associated with tropopause folding. The transport heights for Asian dust during the blocking episode days were found to be associated with the distribution of the isentropes below the IPV At the same time, lee waves propagated by topography affected the downward motion and blocking of Asian dust in China. The Asian dust transported from the dust source regions was deposited by fallout and rain-out with a reinforcing frontogenesis within a surface cyclone, as determined from satellite images using TOMS and GMS5. Accordingly, these results emphasize the importance of forecasting jet streaks, the IPV, and isentropes with geopotential heights in east Asia.

A preliminary study on the correlation between TOMS aerosol index and ground-based measured aerosol optical depth

The aim of this work is to study the correlation between ground-based measured aerosol optical depth (AOD) and TOMS Aerosol Index. For this reason, two AOD data-sets have been analysed. The first set of measurements has been obtained in a desert plateau in Namibia during July 1998, while the second one has been collected in Tito Scalo (Italy), a very small industrial zone surrounded by a large rural area, in June–July 2000. The AOD has been computed in the spectral range 400–870 nm with a resolution of 3 nm by measuring the direct solar irradiance. The used spectroradiometer is an Optical Spectrum Analyser, equipped with a continuously rotating diffraction grating. Successively, a correlation between the Earth Probe TOMS Aerosol Index, whose definition uses backscattered radiances at 331 and 360 nm, and the AOD in the visible range was searched for. A satisfying correlation was found, whose Pearson correlation coefficient R 2 values range from 0.64 to 0.91.

Sahara mineral dust measurements from TOMS: Comparison to surface observations over the Middle East for the extreme dust storm, March 14–17, 1998

A comparison of the TOMS aerosol index (AI) with both measurements of dust concentrations and synoptic data over the Middle East for the extremely heavy dust storm of March 14–17, 1998, is performed. Time series over Algeria, Libya, and Israel yield the following findings: The peak values in both surface concentrations and TOMS data suggest that AI values of 2.5 and 1.2 correspond to surface mean daily concentrations of 1900 and 1000 μg/m3 respectively. Surface concentrations and TOMS maps show that AI values of 3.0 correspond to about 4000 μg/m3. TOMS AI maximum values were found to increase from Algeria to Israel moving along with the center of the dust plume from 0.9 to 2.1 and 2.5 AI values. This seems to be in contradiction with the fact that the plume moves farther away from the major mineral dust sources over the Sahara and may be caused by either an increased vertical extension of the plume, hence increasing the TOMS AI, or due to convergence of the dust plume over the eastern Mediterranean. The size distribution, morphological, and mineralogical composition of the dust analyzed in this study, as well as other aerosol parameters, are essential for improving the remote sensing methods such as the TOMS AI algorithms. Of course, surface measurements alone do not allow the refinement of the TOMS retrievals; vertical profile dust measurements as well as other physical and optical aerosol parameters are necessary.

Determination of radiative forcing of Saharan dust using combined TOMS and ERBE data

We determine the direct radiative forcing of Saharan dust aerosols by combining aerosol information derived from Nimbus‐7 TOMS with radiation measurements observed at the top of atmosphere (TOA) by NOAA‐9 ERBE made during February‐July 1985. Cloud parameters and precipitable water derived from NOAA‐9 HIRS2 were used to aid in screening for clouds and water vapor in the analyses. Our results indicate that under “cloud‐free” and “dry” conditions there is a good correlation between the ERBE TOA outgoing longwave fluxes and the TOMS aerosol index measurements over both land and ocean in areas under the influence of airborne Saharan dust. The ERBE TOA outgoing shortwave fluxes were also found to correlate well with the dust loading derived from TOMS over ocean. However, the calculated shortwave forcing of Saharan dust aerosols is very weak and noisy over land for the range of solar zenith angle viewed by the NOAA‐9 ERBE in 1985. Sensitivity factors of the TOA outgoing fluxes to changes in aerosol index were estimated using a linear regression fit to the ERBE and TOMS measurements. The ratio of the shortwave‐to‐longwave response to changes in dust loading over the ocean is found to be roughly 2 to 3 but opposite in sign. The monthly averaged “clear‐sky” TOA direct forcing of airborne Saharan dust was also calculated by multiplying these sensitivity factors by the TOMS monthly averaged “clear‐sky” aerosol index. Both the observational and theoretical analyses indicate that the underlying surface properties, dust layer height, ambient moisture content, and the presence of cloud all play important roles in determining the TOA direct radiative forcing due to mineral aerosols.

Observations of boreal forest fire smoke in the stratosphere by POAM III, SAGE II, and lidar in 1998

A substantial increase in stratospheric aerosol was recorded between May and October 1998 between 55° and 70°N. This phenomenon was recorded in the absence of reported volcanic eruptions with stratospheric impact potential. The POAM III and SAGE II instruments made numerous measurements of layers of enhanced aerosol extinction substantially higher than typical values 3 to 5 km above the tropopause. A comparison of these observations with lidar profiles, TOMS aerosol index data, and forest fire statistics reveals a strong link between stratospheric aerosol and forest fire smoke. Our analysis strongly suggests that smoke from boreal forest fires was lofted across the tropopause in substantial amounts in several episodes occurring in Canada and eastern Russia. Observations reveal a broad zonal increase in stratospheric aerosol that persisted for at least three months.

Trajectory modeling of aerosol clouds observed by TOMS

An aerosol trajectory model (ATM), which couples TOMS aerosol index (AI) measurements with multiple‐level parcel trajectories, is presented for determining the three‐dimensional (3‐D) distribution of a tropospheric aerosol cloud. The ATM is illustrated with an idealized 2‐D (height‐longitude) cloud in linear vertical shear. The half width of the vertical parcel distribution (an indicator of how well the cloud is resolved) is inversely proportional to time and to vertical shear. The degree to which a cloud can be resolved is limited by an “uncertainty principle,” whereby model precision improves with time, while accuracy degrades with time because of accumulating trajectory errors. ATM is applied to the ash cloud from the September 1992 eruption of Mount Spurr, Alaska. Disagreement in the predicted cloud structure occurs between 3‐day ATM runs using United Kingdom Meteorological Office (UKMO) and National Centers for Environmental Prediction (NCEP) winds. This is due to significant differences in the UKMO and NCEP zonal wind speed near the tropopause, which cause large trajectory separations over 3 days. The UKMO‐predicted cloud range (310–390 K) agrees well with radar and pilot observations of the ash cloud, while the NCEP‐predicted range shows strong disagreement with observations in the region of the jet maximum. This indicates the potential (when independent observations are available) for using ATM to partially validate wind fields.