Barry J. Huebert

Annual contribution of sulfur dioxide to the atmosphere by volcanoes

Abstract The average contribution of SO2 to the atmosphere by volcanoes, estimated largely by extrapolation from direct measurements of volcanic SO2, is calculated to be 18.7 Tg per year. Of this, an estimated 6.8 Tg per year (36%) is from non-erupting degassing volcanoes. Erupting volcanoes yield an average annual flux estimated to be 11.9 Tg SO2 per year (64%). The estimated total annual SO2 output is about 23% larger than the most recent estimate based on direct measurements. Our calculations suggest that 64% of the total comes from erupting volcanoes, as compared to 7% in the earlier estimate. Of the total worldwide annual SO2 flux, 9% is found to be from volcanoes.

Acidity in air and water in a case of warm frontal precipitation

Abstract The acidity of dry air south of a warm front was measured before it ascended producing a large area of warm frontal precipitation. Comparison of the chemical compositions of the dry air and precipitation at cloud base suggest a significant production of both sulfuric and nitric acids in the cloud. Below-cloud processes did not appear to significantly affect the concentration of acids in rain at ground level. Rates of nitric acid and sulfuric acid production in the cloud are estimated.

Calibration and tests of the filter-collection method for measuring clean air ambient levels of nitric acid

Abstract A portable permeation tube based system has been developed for the field calibration of nitric acid vapor collection on Nylon filters during actual atmospheric sampling. Extensive testing has been undertaken to determine the effects of: transfer line materials, the uptake of nitric acid on the filter holder apparatus, the linearity of dilution of the nitric acid effusing from the permeation tube source achievable and the effects of the permeation of gases, other than nitric acid, on the permeation tube calibration. Data demonstrating significant uptake of HNO3 on commonly used materials are given, together with specific recommendations on the use of materials to avoid such problems. Nitrogen dioxide is shown to be a significant contaminant of the HNO3 permeation tubes used requiring corrections of the order of 15%. Nitric acid “spiking” during actual field sampling of clean tropospheric air at a remote site in the Rocky Mountains west of Boulder, Colorado demonstrated agreement between the measured Nylon filter nitrate loading and the calculated loading to + 0.1, −0.4 μg at the 60% confidence level. At the atmospheric sampling rate used of 120 std l min−1, these limits correspond to +5, −20 pptv for a one hour sampling time, with proportionately smaller uncertainties on the mean HNO3 mixing ratio for longer sampling times.

Liquid cloudwater collection using modified Mohnen slotted rods

Slotted rods were used to collect liquid water from summer stratocumulus clouds during the Dycoms program near San Diego. The rods were mounted on a pylon atop the fuselage of NCARs Electra. Their collection efficiency (relative to King probe liquid water content measurements) averaged 84±15% after an initial conditioning period. During collection runs in which the average LWC exceeded 0.1 g/m3, the efficiency averaged 91±12%. We have identified several factors necessary to achieve this level of performance.

Wind Speed and Sea State Dependencies of Air‐Sea Gas Transfer: Results From the High Wind Speed Gas Exchange Study (HiWinGS)

A variety of physical mechanisms are jointly responsible for facilitating air-sea gas transfer through turbulent processes at the atmosphere-ocean interface. The nature and relative importance of these mechanisms evolves with increasing wind speed. Theoretical and modeling approaches are advancing, but the limited quantity of observational data at high wind speeds hinders the assessment of these efforts. The HiWinGS project successfully measured gas transfer coefficients (k660) with coincident wave statistics under conditions with hourly mean wind speeds up to 24 m s−1 and significant wave heights to 8 m. Measurements of k660 for carbon dioxide (CO2) and dimethylsulfide (DMS) show an increasing trend with respect to 10-meter neutral wind speed (U10N), following a power-law relationship of the form: k660 co2~U10N1.68 and k660 dms~U10N1.33. Among seven high wind speed events, CO2 transfer responded to the intensity of wave breaking, which depended on both wind speed and sea state in a complex manner, with k660 co2 increasing as the wind sea approaches full development. A similar response is not observed for DMS. These results confirm the importance of breaking waves and bubble injection mechanisms in facilitating CO2 transfer. A modified version of the Coupled Ocean-Atmosphere Response Experiment Gas transfer algorithm (COAREG ver. 3.5), incorporating a sea state-dependent calculation of bubble-mediated transfer, successfully reproduces the mean trend in observed k660 with wind speed for both gases. Significant suppression of gas transfer by large waves was not observed during HiWinGS, in contrast to results from two prior field programs.

Variability of sulfate aerosol concentrations at Mauna Loa observatory, Hawaii

Daily total particulate matter observations of sulfate, sodium, and methanesulfonate were collected at Mauna Loa Observatory (19.54°N, 155.57°W, 3397m ASL) during 1995-2008. Observations were restricted to nighttime, downslope conditions and were thus representative of free tropospheric air masses. In this paper we focus analyses on 2008, when active volcanoes in Hawaii, Alaska, Indonesia, and elsewhere may have perturbed the northern hemisphere sulfur budget. The 2008 seasonal cycle of aerosol species was broadly consistent with the 1995-2008 mean, although the springtime peaks of anthropogenically-derived sulfate were larger than typical. Trajectories originated from East Asia less frequently and from North America more frequently in spring 2008 than in the long term data record, possibly linked to the strong La Nina conditions that year.

Meeting Review: Airborne Aerosol Inlet Workshop 27-28 February and 1 March 1991

The aerodynamic design of airborne probes for the capture of air and aerosols is discussed. Emphasis is placed on the key parameters which effect the proper sampling such as inlet lip design, internal duct components for low pressure drop, and exhaust design. Inlet designs which avoid sonic flow conditions on the lip and flow separation in the inlet are shown. Cross-stream velocities of aerosols are expressed in terms of droplet density and diameter. Since flow curvature can cause aerosols to cross streamlines and impact probe walls, minimal flow curvature can be accomplished by proper inlet design, probe orientation, and the avoidance of bends upstream of the test section. A NASA panel code called PMARC has been used successfully to compute streamlines around aircraft and probes as well as the local velocity and pressure distributions in inlets. An NACA 1-series inlet with modified lip radius has been used for the airborne capture of ozone at high altitude and high flight speed. The device has a two-stage inlet which allows a large deceleration on the inflow with little disturbance to the flow through the test section. Diffuser design, exhaust hood design, valve loss, and comer vane geometry are discussed. NOMENCLATURE A0 diffuser outlet flow area, m 2 AO diffuser inlet flow area, m2 b wing span, m c wing aerodynamic chord=S/b, m CL wing lift coefficient d duct diameter, m ddiameter of aerosol droplet or particle, m kv total pressure loss coefficient, Ap/q Ldif streamwise length of diffuser, m L wing lift, N q dynamic pressure, N/m2 r distance from vortex core to induced streamline or distance from wing quarter chord to upwash location (Figure 1), m