C. C. Van Valin

Cloud nucleus formation in a power plant plume

Abstract A rate of production of ca 10 16 particles s −1 of H 2 SO 4 aerosol that acts as cloud condensation nuclei at 1% supersaturation has been estimated to take place in the emission plume from the Four Comers power plant near Farmington, N.M. This generating plant produces about 2175MW at full capacity and emits about 3.7kgs −1 of SO 2 , 2.2 kgs −1 of NO x , and 0.9 kgs −1 of particulates. The site area is desert; annual precipitation averages around 15cm, daytime relative humidity is typically 10–20% and annual sunshine is 75% of possible. An instrumented aircraft was utilized during five investigative periods over a 2-year span to measure plume parameters and to collect plume aerosol samples. The estimated production rate of 10 16 particles s −1 in the plume is equivalent to a gas phase oxidation of SO 2 and homogeneous nucleation-condensation of about 5 μg m −3 h −1 of H 2 SO 4 and is consistent with this mechanism being the primary route for removal of SO 2 .

Continuous atmospheric sulfur gas measurements aboard an aircraft: A comparison between the flame photometric and fluorescence methods

Abstract Analyzers that use the flame photometric and pulsed fluorescence techniques measured trace concentrations of S gas aboard an instrumented aircraft. Concentrations in the range of 1–20 ppbv were found at various locations over the U.S. East Coast and near Bermuda at altitudes up to 4000 m (650 mb). The response of both instruments changes significantly with ambient air pressure. In the case of the fluorescence method, a simple correction is applied to both the zero and span values. For the flame photometric instrument, the correction is more complicated, less accurate and valid only for ambient air pressures above 750 mb. A comparison between the two methods, based on several thousand 1-min averages, shows that the flame photometer produced consistently larger concentrations (27%) than the fluorescence device. Additional comparisons between the continuous monitors aboard the NOAA King Air and similar instruments aboard other aircraft sampling in parallel produced reasonable agreement.The use of two different techniques for measuring S gas establishes a range in the S gas concentration. This range is meaningful, since it delineates the contributions of the various interferences.

Lake Michigan Ozone Study (LMOS): Measurements from an instrumented aircraft

Abstract As part of the Lake Michigan Ozone Study, the NOAA instrumented King Air research aircraft made a series of flights over Lake Michigan during the summers of 1990 and 1991 to characterize the atmospheric conditions prevailing during times when O 3 concentrations exceeded the air quality standard. Most of the time, O 3 concentrations were within the normal range (40–70 ppbv) for the location and season, but higher concentrations were measured during the afternoon flights at several isolated locations. During three afternoon flights, high O 3 concentrations (> 120 ppbv) were observed along portions of the flight path; the highest 1-min average exceeded 160 ppbv. In two flights the highest O 3 concentrations were observed in the lower boundary layer over the eastern portion of the flight track; in one case the high concentrations were found over the western side of the lake throughout the boundary layer. The increased O 3 was accompanied by moderately increased SO 2 and NO x (10–20 ppbv); outside the region of elevated O 3 , the SO 2 and NO x were less than 2–3 ppbv. The elevated zone concentrations were related to emissions from the urban region located near the southern and southwestern shores of Lake Michigan.

Fine particle formation and transport in the Colstrip, Montana, powerplant plume

Abstract Smoke plumes of greater width but lesser thickness than predicted by Gaussian diffusion models have been documented by measurements from aircraft of the Colstrip, Montana, powerplant plume at downwind distances of 4–25 km. The plume has also been shown to be deflected as much as 20° away from the prevailing wind direction by the terrain. A particle formation rate of ~ 1016 s−1 in the plume over down-wind distances of 25–30 km has been estimated by using the plume profile measurements.

Aerosol and cloudwater properties at whiteface mountain, New York

A field program for the measurement of the physical and chemical properties of aerosols and clouds was conducted at Whiteface Mountain, N.Y., during an 8-week period in June, July, and August 1983. Analysis of two-stage Nuclepore filter samples by proton-induced X-ray emission (PIXE) spectroscopy showed that most (85 to 90%) of the aerosol sulfate was in the accumulation mode (modal radius r - 0.1 μm) and that ≅90% of total sulfate originated southwest of the Whiteface Mountain site. During a typical pollution episode originating in the Midwest, the total aerosol sulfate concentration was 19 pg m −3, or 63 of total dry aerosol, which was - 30 gg m− s. Scavenging of sulfate aerosol by clouds was found to be greater than 95% efficient in clouds of 0.5gm−3 liquid water content. Measured pH values when the air mass trajectories were from the southwest were systematically lower than when the trajectories were from the northwest or northeast, i.e., 3.4 vs 4.4 and 4.8. In the southwest sector water samples, S04−2 and N03− were highly correlated to each other and to free H+, Ca2−, Cl−, Pb, and Ba.

Air pollution measurements at the boulder atmospheric observatory

Pollution episodes of three distinct types were detected at the Boulder Atmospheric Observatory, which is a 300 m instrumented tower located in a rural area 25 km north of Denver and 20 km east of Boulder. Under stably stratified atmospheric conditions, usually at night or early morning, both power-plant-derived and general urban plumes were sampled. The powerplant plumes were characterized by SO2 concentrations of 30 to 50 ppb in the plume centers, NO2 maxima of 20 to 40 ppb on the plume edges, NO maxima of as much as 50 ppb in the plume centers, and the absence of O3 from the plume centers. Light scattering (bscat), principally due to coarse particles, was typically enhanced by 20 to 40%, relative to nominally clean air. The urban plumes typically contained NO2 uniformly distributed throughout the affected air mass at 20 to 30 ppb, no detectable NO or SO2, and O3 present at concentrations less than half that in background air; bscat was typically increased by a factor of 2 to 3. A third type of pollution episode, containing greatly increased concentrations of condensation nuclei, was observed during days when surface heating had apparently stimulated biological particle production. At these times the usual indicators of anthropogenic pollution were absent.

Cloud and ice nuclei from human activities

Abstract Aerosol characteristics (i.e. light scattering, Aitken nuclei (AN), cloud condensation nuclei (CCN), ice nuclei (IN), and chemical composition of individual particles) were measured during the “Brown Cloud” experiment near Denver, Colorado, during November 1973. Our measurements show that 1. (1) light scattering and the atmospheric concentration of CCN are directly and positively correlated with pollution intensity; 2. (2) formation of CCN and light scattering particles is accelerated by sunlight; 3. (3) natural production of IN during windy periods greatly exceeds man-made production during pollution episodes; 4. (4) the fraction of aerosol particles containing lead increases during a pollution episode; 5. (5) lead, chlorine and bromine are found mostly in particles dia., which may coagulate with larger, predominantly siliceous particles.