ISSN:0148-0227    

DOI:10.1029/JD090iD01p02075

年代:1985

数据来源: WILEY

摘要:

Concurrent measurements of the dry deposition of sulfate, particulate sulfur, nitrate, sulfur dioxide, ozone, and nitric acid were made during September 1981 and June 1982, using several independent methods. The measurements were conducted at a common site, which was a grasscovered 32‐ha field in a topographically flat, rural area 14 km southwest of Champaign, Illinois. Research groups from 14 U.S. and Canadian institutions participated in the study, which was coordinated by the Illinois State Water Survey. Micrometeorological methods such as eddy correlation, variance, concentration gradient/modified Bowen ratio calculation, and eddy accumulation were used. Deposition collection methods such as surrogate surface sampling and vegetation washing were also employed. Sampling schedules and heights of measurements were arranged to maximize the comparability of results from the various flux determination techniques. Sulfate and particulate sulfur mean deposition velocities,vd, on the order of 0.3 cm/s were found by several methods. Nighttime values were small, generally near zero, while daytimevdof up to 1.0 cm/s were observed. A possibly significant contribution to the total sulfur flux by large (diameter>2.0 μm) particle associated sulfate was noted in some periods. Daytime sulfur dioxide and nitric acidvdof greater than 3.0 cm/s were measured, suggesting near‐zero vegetation canopy resistance to mass transfer for these g

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02076

年代:1985

数据来源: WILEY

摘要:

We measured the dry flux of nitric acid vapor to a pasture near Champaign, Illinois during June of 1982. The mass flux was determined by a modified Bowen‐ratio method, employing the surface sensible heat flux and temperature and concentration variations with altitude. We found the daytime average deposition velocity to be 2.5±0.9 cm/s. The average canopy (stomatal and adsorption) resistance averaged virtually zero. The measured June dry flux of HNO3was of the same magnitude as the wet flux measured near

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02085

年代:1985

数据来源: WILEY

摘要:

Instrumentation for the measurement of the dry deposition velocity of SO2by the concentration gradient method has been developed. The instrumentation consists of a sensitivity enhanced Meloy SA260 sulfur analyzer together with appropriate sampling hardware. The system was field tested at the U.S. EPA sponsored dry deposition intercomparison study held in June 1982 at Champaign, Illinois.

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02091

年代:1985

数据来源: WILEY

摘要:

Atmospheric fluxes of momentum, sensible heat, water vapor, ozone, and sulphur were measured on 10 days during the intercomparison study. Computed mean daytime (averagez/L= −0.33) deposition velocities were 0.47 cm/s for ozone and 0.33 cm/s for sulphur, while for measurements during the early evening (averagez/L= 0.27), the mean deposition velocities decreased to 0.35 and 0.21 cms, respectively. These deposition velocities have been corrected to account for the slow time response (time constant near 1.1 s) of the pollutant analyzers. The corrections were based on computed effects of a similar time response on temperature‐vertical velocity cospectra. These were found to be stability dependent and ranged from about an additional 20% in unstable atmospheres to factors of 2–3 for stable conditions. Eddy correlation measurements were also attempted for particulates using a laser particle spectrometer. Subsequent analysis revealed that for our combinations of sample flow rate and the ambient concentrations, deposition velocities were too small to be distinguished from the inherent Poisson uncertainty in particle counting. This implied that for particles of diameters 0.1–0.5 μm deposition velocities were less than 0.05 cm/s, assuming no source for particles below our measurin

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02097

年代:1985

数据来源: WILEY

摘要:

Simultaneous surface layer ozone flux measurements by eddy flux and profile methods are reported with supporting micrometeorological data. The results show a close correspondence between the eddy diffusivities of ozone and sensible heat rather than momentum eddy diffusivity. Ozone deposition velocities are computed both from the eddy flux and profile fluxes of ozone. As with eddy diffusivities, these results clearly show the sensible heat analogy giving the better fit with the eddy flux values. These sets of deposition velocities also have a consistent temporal variation, with peak values of up to 1 cm/s at midday changing to less than 0.1 cm/s in the evening.

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02111

年代:1985

数据来源: WILEY

摘要:

An eddy accumulator was developed and operated during the Dry Deposition Intercomparison Study at Champaign, Illinois, in June 1982. The system collected paired samples for water vapor and particulate sulfate flux measurements, one sample for upward eddies and the other for downward eddies. Nineteen water vapor samples were analyzed gravimetrically, and two sulfate samples were analyzed by ion chromatography. Comparison of water vapor results with eddy correlation measurements showed that discrepancies exceeded predicted errors. No significant results were obtained from the sulfate samples.

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02119

年代:1985

数据来源: WILEY

摘要:

Measurements of SO42−fluxes to surrogate surfaces have been conducted as part of the Dry Deposition Intercomparison Study in Champaign, Illinois. Data for Teflon plates without rims and for polycarbonate petri dishes with 1‐cm rims have been obtained and compared with data for Teflon sheets and polyethylene dustfall buckets used by other investigators. Results show that deposition velocities for the Teflon plates are in the range of 0.17–0.42 cm/s, while corresponding values for the petri dishes are in the range of 0.18–0.61 cm/s. Comparisons among the four types of surrogate surfaces show deposition velocities which increase in the order Teflon sheets ∼ Teflon plates

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02123

年代:1985

数据来源: WILEY

摘要:

Eddy correlation measurements of participate sulfur fluxes at the 1981 and 1982 Dry Deposition Intercomparison Experiments indicate a strong diurnal variation in deposition velocity (downward flux divided by concentration, at a height near 6 m). Most of the run‐to‐run variability for data collection periods of 30 min seems to be due to unwanted sensor noise. Systematic changes of fluxes wth height due to possible advection from strong point sources of sulfur can occur but should be quite small. A parameterization for deposition velocity is derived in terms of friction velocityu* and the Obukhov stability length scaleL. When the parameterization is applied in conjunction with nearly continuous measurements of mean micrometeorological variables such as wind speed and temperature difference, the resulting long‐term mean deposition velocity found is 0.22±0.06 cm/s with a variation greater than ±50% from day to day, depending on local atmospheric conditions. Peak deposition velocities greater than 0.5 cm/s occur on windy afternoons. Such values are considerably greater than suggested from wind‐tunnel and theoretical investigations, but are similar to past results obtained by use of the same techniques over lush vegetation. Boundary layer convective motions that increase wind gustiness near the surface seem to increase particle deposition velocities considerably. Relatively small deposition velocities are found in neutral and stable atmospheric conditions or over surfaces that lack complex fine

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02131

年代:1985

数据来源: WILEY

摘要:

Eddy correlation flux measurements of total atmospheric aerosol particulates were collected over a grass surface at Champaign, Illinois, in June 1982. PMS ASAS‐300A and Royco 225 optical particle counters were used as sensors to measure fluxes in four size ranges from 0.15 to 2.5 μm. The fluxes were quite variable, both in time and between sensors. The sensor signals are also quite noisy, but we demonstrate that, with certain limitations, the sensor systems are suitable for making flux measurements. This variability in the flux measurements is, in part, a result of the sensor noise and is also at times possibly the result of the transport through vertical moisture gradients, flux divergence, and changes in particulate concentration. However, frequent occurrences of upfluxes indicate it is also possibly the result of organic emissions from the surface. Ensemble average deposition velocities for each sensor were negative and quite small and, in most cases, not statistically significant. However, daily average values were often quite large and negative and showed good agreement between senso

ISSN:0148-0227    

DOI:10.1029/JD090iD01p02145

年代:1985

数据来源: WILEY