Southern Ocean (SO) air is amongst the most pristine on Earth, particularly during winter. Historically, there has been a focus on biogenic sources as an explanation for the seasonal cycle in cloud condensation nuclei concentrations (NCCN). NCCN is also sensitive to the strength of sink terms, although the magnitude of this term varies considerably. Wet deposition, a process encompassing coalescence scavenging (drizzle formation), is one such process that may be especially relevant over the SO. Using a boundary layer cloud climatology, NCCN and precipitation observations from Kennaook/Cape Grim Observatory (CGO), we find a statistically significant difference in NCCN between when the upwind meteorology is dominated by open mesoscale cellular convection (MCC) and closed MCC. When open MCC is dominant, a lower median NCCN (69 cm−3) is found compared to when closed MCC (89 cm−3) is dominant. Open MCC is found to precipitate more heavily (1.72 mm day−1) and more frequently (16.7% of the time) than closed MCC (0.29 mm day−1, 4.5%). These relationships are observed to hold across the seasonal cycle with maximum NCCN and minimum precipitation observed during Austral summer (DJF). Furthermore, the observed MCC morphology strongly depends on meteorological conditions. The relationship between NCCN and precipitation can be further examined across a diurnal cycle during the summer season. Although there was again a negative relationship between precipitation and NCCN, the precipitation cycle was out of phase with the NCCN cycle, leading it by ~3 hours, suggesting other factors, specifically the meteorology play a primary role in influencing precipitation.

A simple numerical experiment demonstrates that the reduced major axis regression, rather than standard linear regression, is likely to be the method of choice for the regression analysis of air quality datasets. The case used for illustration is that of determining equivalence of alternative PM10 measurement systems.

Characterization of atmospheric aerosols collected in the northeast part of the Amazon Basin is presented. The main aerosol source in that region is the forest natural biogenic emission, The aerosol samples were collected using stacked filter units, and were analyzed applying several analytical techniques: Particle Induced X-ray Emission (PIXE) for the quantitative analysis of trace elements with Z > 11; Particle Induced Gamma-ray Emission (PIGE) for the quantitative analysis of Na; Ion Chromatography (IC) was used to quantify ionic contents of aerosols from the fine mode particulate samples. A reflectance technique was used in order to measure black carbon concentrations; Gravimetric analysis was used in order to determine the total atmospheric aerosol mass concentration. The comparison from PIXE and IC concentration measurements for S, K and Ca techniques were in an excellent agreement. A good agreement was also obtained for Na concentrations measured by PIGE and IC techniques. Multivariate statistical analysis was used in order to identify and characterize the sources of the atmospheric aerosol present in the sampled region. The Serra do Navio aerosol is characterized by biogenic emissions, responsible for the majority of the total fine mass concentration, A strong marine influence was also noted. Soil dust is also an important aerosol source in that region. (C) 1998 Elsevier Science B.V.

A field project encompassing wet-only rainwater sampling was initiated as a bilateral Fiji/Australia activity. Normally, biweekly samples were collected, using a wet-only rainwater sampler, and analysed for H+, Na+, K+, Mg2+, NH4+, Cl−, NO3−, SO42−, PO43-, methane sulphonic acid, oxalic acid, formic acid and acetic acid. The pH of the rainwater ranged between 5.730 and 4.480 with an average value of 5.176, slightly lower than the pH of unpolluted rainwater saturated with atmospheric CO2(pH = 5.650). Na+and Cl−were the major ions with average concentrations of 98.15 M and 109.57 M respectively. There is an excellent correlation between the cation sum (average 147.71 eq L-1) and the anion sum (average 142.12 eq L-1) attesting to the quality of the data generated. This paper presents the detailed results of the study for a relatively clean remote island site in Suva, Fiji, latitude 18° 09‘ S, longitude 178° 27’ E, height 6 m, and outlines prospects for further work.

A multi-year data set on rainwater composition obtained by the Royal Observatory, Hong Kong, as a contribution to the Global Atmosphere Watch of the World Meteorological Organization, has been reviewed in terms of data quality and evaluated for evidence of acidification due to anthropogenic emissions of acid precursors. Elevated levels of acidic sulphate and nitrate are evident in the data, which, when combined with a preliminary estimation of dry deposition fluxes of acidic gases, suggest a total acid deposition flux of approximately 160 meq m−2 yr−1. This value is sufficiently high so as to suggest the need for integrated assessment of acidic deposition and potential environmental consequences in the region.

An existing ecological model of DMS production has been extended and applied to the spring-summer period in the Subantarctic Southern Ocean. The model predicts that production of phytoplankton and dissolved DMS will increase during spring to reach a maximum in summer consistent with the atmospheric data collected at the Cape Grim baseline station. Archival Coastal Zone Color Scanner satellite imagery has been used to define the seasonal range in phytoplankton concentration in the study region and validate model predictions. Local measured wind and sea temperature data have been used to calculate the DMS transfer velocity which is used to compute the sea-to-air flux of DMS. The seasonal trend in predicted DMS flux is in good agreement with the flux estimates made from observations.

The width of a smoke plume from an isolated ore smelter in the tropics has been found from airborne measurements of total particle concentrations at distances up to 560 km from the source under cloudless, inversion-limited, convective conditions over flat terrain. Results are surprisingly similar to estimates derived from the few available relevant experiments, most of which were conducted in different meteorological circumstances and using quite different techniques.