Rudolf B. Husar

Asian dust events of April 1998

On April 15 and 19, 1998, two intense dust storms were generated over the Gobi desert by springtime low-pressure systems descending from the northwest. The windblown dust was detected and its evolution followed by its yellow color on SeaWiFS satellite images, routine surface-based monitoring, and through serendipitous observations. The April 15 dust cloud was recirculating, and it was removed by a precipitating weather system over east Asia. The April 19 dust cloud crossed the Pacific Ocean in 5 days, subsided to the surface along the mountain ranges between British Columbia and California, and impacted severely the optical and the concentration environments of the region. In east Asia the dust clouds increased the albedo over the cloudless ocean and land by up to 10–20%, but it reduced the near-UV cloud reflectance, causing a yellow coloration of all surfaces. The yellow colored backscattering by the dust eludes a plausible explanation using simple Mie theory with constant refractive index. Over the West Coast the dust layer has increased the spectrally uniform optical depth to about 0.4, reduced the direct solar radiation by 30–40%, doubled the diffuse radiation, and caused a whitish discoloration of the blue sky. On April 29 the average excess surface-level dust aerosol concentration over the valleys of the West Coast was about 20–50 μg/m3 with local peaks >100 μg/m3. The dust mass mean diameter was 2–3 μm, and the dust chemical fingerprints were evident throughout the West Coast and extended to Minnesota. The April 1998 dust event has impacted the surface aerosol concentration 2–4 times more than any other dust event since 1988. The dust events were observed and interpreted by an ad hoc international web-based virtual community. It would be useful to set up a community-supported web-based infrastructure to monitor the global aerosol pattern for such extreme aerosol events, to alert and to inform the interested communities, and to facilitate collaborative analysis for improved air quality and disaster management.

Characterization of tropospheric aerosols over the oceans with the NOAA advanced very high resolution radiometer optical thickness operational product

The National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) is an instrument on a polar orbiting satellite that provides information on global aerosol distributions. The remote sensing algorithm is based on measurements of backscattered solar radiation which yield a measure of the radiatively equivalent aerosol optical thickness τ A sat (EAOT) over the oceans. Seasonally composited EAOT data for the period July 1989 to June 1991 reveal many spatially coherent plume-like patterns that can usually be interpreted in terms of known (or reasonably hypothesized) sources in association with climatological wind fields. The largest and most persistent areas of high EAOT values are associated with wind-blown dust and biomass burning sources; especially prominent are sources in Africa, the middle East, and the Asian subcontinent. Prominent plumes over the midlatitude North Atlantic are attributed to pollution emissions from North America and Europe. Large plumes attributed to pollution aerosols and dust from sources in Asia are clearly visible over the western and central North Pacific. On a global scale the annually averaged northern hemisphere EAOT values are about 1.7 times greater than those in the southern hemisphere. Considering each hemisphere separately, EAOT values in summer are about twice those in winter. Within the midlatitude band 30°-60° (i.e., where anthropogenic emissions are greatest) the summer/winter ratio is about 3. The temporal variability of monthly mean EAOT in specific ocean regions often shows characteristic seasonal patterns that are usually consistent with aerosol measurements made in the marine boundary layer. Nonetheless, there are features in the EAOT distributions that can not be readily interpreted at this time. The AVHRR EAOT distributions demonstrate that satellite products can serve as a useful tool for the planning and implementation of focused aerosol research programs and that they will be especially important in studies of climate-related processes.

Estimating historical anthropogenic global sulfur emission patterns for the period 1850-1990

Abstract It is important to establish a reliable regional emission inventory of sulfur as a function of time when assessing the possible effects of global change and acid rain. This study developed a database of annual estimates of national sulfur emissions from 1850 to 1990. A common methodology was applied across all years and countries allowing for global totals to be produced by adding estimates from all countries. The consistent approach facilitates the modification of the database and the observation of changes at national, regional, or global levels. The emission estimates were based on net production (i.e., production plus imports minus exports), sulfur content, and sulfur retention for each countrys production activities. Because the emission estimates were based on the above considerations, our database offers an opportunity to independently compare our results with those estimates based on individual country estimates. Fine temporal resolution clearly shows emission changes associated with specific historical events (e.g., wars, depressions, etc.) on a regional, national, or global basis. The spatial pattern of emissions shows that the US, the USSR, and China were the main sulfur emitters (i.e., approximately 50% of the total) in the world in 1990. The USSR and the US appear to have stabilized their sulfur emissions over the past 20 yr, and the recent increases in global sulfur emissions are linked to the rapid increases in emissions from China. Sulfur emissions have been reduced in some cases by switching from high- to low-sulfur coals. Flue gas desulfurization (FGD) has apparently made important contributions to emission reductions in only a few countries, such as Germany.

Haze trends over the United States, 1980-1995

The patterns and trends of haze over the United States for the period of 1980–1995 are presented. Haze measurements are based on human visual range observations at 298 synoptic meteorological stations operated by the United States Weather Service. There was a significant (B10%) decline in haziness over the 15-yr period. The reductions were evident throughout the eastern United States as well as over the hazy air basins of California. During the same period, in the eastern United States sulfur emissions also declined by about 10%. However, a causality for the reductions has not been established. This report is an update of an earlier survey of haze patterns and trends from 1950 to 1980. r 2001 Elsevier Science Ltd. All rights reserved.

SULFUR BUDGET OF A POWER PLANT PLUME

As part of the Midwest Interstate Sulfur Transformation and Transport (MISTT) study, the summer sulfur budget of the plume of the 2400 MW coal-fired Labadie power plant near St. Louis, Missouri is assessed via aircraft data, ground monitoring network data and a two-box model. The paniculate sulfur (Sp) formation rate is obtained from three-dimensional plume mapping combined with a high time-resolution Sp sampling technique. During noon hours the SO2 conversion rate is found to be 1–4% per hour, compared to night rates below 0.5% per hour. Plume excess light scattering coefficient (bscat) and excess Sp correlated well (r = 0.87), indicating most Sp is formed in the light-scattering size range. During daytime the well-mixed plume is transported at 5ms−1 on the average; at night the July average wind speed at plume height is 12ms−1 due to the low-level jet The nocturnal plume is less than 100 m thick at 400 m above ground and is decoupled from the surface until morning. Ground monitoring data from the Regional Air Pollution Study (RAPS) show that plume entrainment into the rising mixing layer is completed by 1000 Central Daylight Time (CDT). Due to daytime vertical mixing and nocturnal decoupling, the dry removal rate for the elevated plume is highest near noon. In a daily cycle, the plume sequentially passes through a reservoir regime, dissociated from delivery to the ground and then enters the mixing-removal regime. A two-box model representing the two regimes, with diurnally periodic rate constants for transformation and removal, is employed to estimate plume sulfur budgets. Ignoring wet removal, 30–45% of the SO2 is estimated to be converted to Sp, half within the first day. Particulate sulfur is formed unevenly: the afternoon plume contributes more than its share because it rises so high that it has more time to react before removal begins. In short: transformation and removal occur mainly during the daytime, while transport is fastest at night. After a hard day of convection, reaction and deposition, the lower atmosphere relaxes at dusk while the midwestern plume takes off overnight on a jetstream and begins the next days work 300–400 km from the stack.

An eddy-correlation measurement of particulate deposition from the atmosphere

Abstract Eddy-correlation measurements of the vertical flux of particles in the size range of 0.05-0.1 μm indicate that the deposition velocity at 5 m above a moderately rough surface varies from 1.0-0.1 cm s −1 in light winds. These velocities are only slightly less than the corresponding estimates for momentum and a few gases that are highly reactive at the surface.

Spatial and temporal pattern of eastern U.S. haziness: A summary

Abstract One of the key features of the optical environment over the eastern U.S. is the frequent occurrence of regional haziness, particularly during the summer season. Four historical data bases were examined for estimation of the regional trend in haziness over the past 80 years: the surface visibility observations currently operated by the National Weather Service; historical visibility at Blue Hill MA; the NOAA-WMO turbidity network measuring the extinction of solar radiation with a sun photometer since the 1960s; and a set of direct solar radiation monitoring stations operated since 1910. In the 1970s the lowest visibility occurred in the region of the Ohio River. The strongest increase of haziness was noted in the states adjacent to the Smoky Mountains: the average visibility there has decreased from 24 to 10 km since 1948. That region also exhibits the highest turbidity (vertical optical depth of the aerosol). The spatial trends of coal consumption indicate a consistency with the spatial trends in haziness.

Relationships between Aerosol Extinction Coefficients Derived from Airport Visual Range Observations and Alternative Measures of Airborne Particle Mass

Epidemiological assessments of population exposures to airborne particles are often hampered by the scarcity of available fine particle mass measurements. In an attempt to overcome this serious problem, we analyze In this paper methods for predicting fine particle (M 1) and Inhalable particle (IP) mass concentrations using relative humidity corrected light extinction coefficient (b ext) estimated from airport visual range (V r) observations. The analyses presented are based on theoretical determinations as well as statistical investigations utilizing EPAs NASN and Inhalable Particle Monitoring Network (IPMN) data bases and routine airport visual range observations In twelve large U.S. cities. Our results Indicate that, after controlling for certain limitations of airport visual range data, most of the regression models developed in this paper can be applied satisfactorily to predict M t and IP. Furthermore, our findings Indicate that a more representative formula than the commonly used meteorological ran...

Continuous in situ monitoring of ambient particulate sulfur using flame photometry and thermal analysis

Abstract The sulfur component of the St. Louis ambient aerosol has been continuously monitored using a flame photometric detector (FPD) to measure particulate sulfur concentration, and in situ thermal analysis to chemically analyze the aerosol for H 2 SO 4 and its ammonium salts, NH 4 SO 4 , (NH 4 ) 3 H(SO 4 ) 2 , and (NH 4 ) 2 SO 4 . During the sixteen day monitoring period, the sulfate aerosol varied with respect to chemical composition, but tended to be in the form of the ammonium salts rather than in the form of sulfuric acid. Comparison of particulate sulfur levels with the light scattering coefficient during the monitoring period indicates that particulate sulfur was a significant constituent of the light scattering aerosol, but its mass accounted for less than half of the mass of the light scattering aerosol.

Project mistt: Kinetics of particulate sulfur formation in a power plant plume out to 300 km

Abstract As part of the 1976 field program of Project MISTT, the plume of the coal-fired Labadie power plant near St Louis was positively identified and sampled from aircraft over a range exceeding 300 km and 10 h of transport during day and night on July 9 and July 18. Measurements were made of SO 2 , NO x , ozone, particulate sulfur and various other pollutant and meteorological parameters. For both days, it is found that the gas-to-particle conversion of sulfur occurred mostly during daylight hours. The ratio of particulate to total sulfur was related linearly with the total solar radiation dose experienced by the plume. The maximum rate of paniculate sulfur formation was less than 3%h −1 on both days. Production of ozone was also observed within the plume on both occasions. Ground removal of total sulfur was found to be about 25% in the first 200 km, and its magnitude is compared to that of the gas-to-particle conversion.