Jorgen B. Jensen

The mixture state of individual aerosol particles in the 1997 Indonesian haze episode

Abstract The mixture state of individual aerosol particles collected at altitudes of 1– 5 km on 23 and 25 October 1997, from an aircraft flying over southern Kalimantan during the 1997 Indonesian forest fires, has been examined using the dialyses of water-soluble material with water, and organic material with benzene in conjunction with electron microscopy. Individual aerosol particles in the radius range of 0.1– 2 μm were mainly present as an internal mixture of water-soluble organic material and inorganic salt (mainly ammonium sulfate). Although material comprised of chain aggregations of electron-opaque spherules (elemental carbon) was also found, the proportion of these was small.

Some optical properties of smoke aerosol in Indonesia and tropical Australia

Aerosol light-scattering coefficient at 530 nm and its hygroscopic growth were determined in biomass-burning smoke in the lower atmosphere over Kalimantan and northern Australia during the 1997 dry-season fires. Both in and away from plumes, light-scattering was considerably greater in the Indonesian region and hygroscopic growth in scattering was also consistently greater. The relative increase in scattering, from 20% to 80% relative humidity, was typically 1.37 in northern Australian and 1.65 in Kalimantan. Limited aerosol light absorption data indicate relatively small absorption in the Indonesian smoke. In part these differences can be explained by different combustion phases, mixed flaming and smoldering in the Australian savanna fires compared with predominantly smoldering in Indonesia, although these and other concurrent measurements suggest that underground peat combustion may have made a significant contribution to the Indonesian smoke.

Very high weight ratios of S/K in individual haze particles over Kalimantan during the 1997 Indonesian forest fires

Abstract The elemental composition of individual aerosol particles of 0.15–3xa0μm radius, collected over Kalimantan during the 1997 Indonesian forest fire event, was analyzed using a transmission electron microscope equipped with an energy-dispersive X-ray analyzer (EDX). Although 60–90% of the particles collected at altitudes of 1–5xa0km contained K, they exhibited high weight ratios of S/K with median values of 9–18 independent of particle size. These were much larger than those (median values of 2–4) obtained from the forest fires in northern Australia. The high weight ratios over Kalimantan are considered to be due to the heterogeneous growth of particles through the oxidation of SO2. In addition to SO2 from the combustion of forest biomass, SO2 originating from the combustion of peat below the ground is believed to have been important in producing the high S/K ratios.

Tropospheric carbon monoxide and hydrogen measurements over Kalimantan in Indonesia and northern Australia during October, 1997

During the PACE-5 campaign over Australia and Indonesia in October 1997, we used an aircraft to measure carbon monoxide (CO) and hydrogen (H2). Latitudinal distributions of CO and H2 clearly showed a large increase from northern Australia to Kalimantan in Indonesia. Elevated CO levels over northern Australia were observed only in the smoke plumes of savanna fires. A thick smoke haze from forest fires over Kalimantan contained very high CO mixing ratios of 3 to 9 ppm. These enhanced CO mixing ratios correlated well with increased concentrations of H2, nitrogen oxides (NOx), and aerosols. Emission ratios from biomass burning in Kalimantan ranged 0.06 0.1 for H2/CO (ppb/ppb), 0.0002 to 0.0005 for NOx/CO (ppb/ppb), and 0.43 to 1.0 for number of aerosols/CO (cm−3/ppb). These values were much lower than emission ratios in northern Australia. This difference suggests that the biomass burning in Indonesia was intense and that, due to a strong El Nino event, an unique composition of trace gases was formed in the smoke haze.

Precipitation in marine cumulus and stratocumulus.: Part I: Thermodynamic and dynamic observations of closed cell circulations and cumulus bands

Abstract A case study of vigorous drizzle development in marine boundary layer clouds is presented. The clouds were observed using a research aircraft west of Tasmania during the Southern Ocean Cloud Experiment. A clean marine boundary layer contained both cumulus clouds (some oriented in bands) and an upper level stratus deck organised in a closed cell circulation. “Cold pools,” that is regions of evaporatively cooled air under mature cumulus clouds, were observed on several occasions. Air in the cold pool centre showed a divergent component of the wind perpendicular to the mature cumulus bands. Ahead of this spreading precipitation downdraft, the wind component perpendicular to the cumulus band was convergent, and new cumulus clouds were subsequently formed over these regions. This dynamical situation is likened to an actively developing squall line of the propagating type. The development of drizzle, and its evaporation in the mixed-layer below the base of mature cumulus bands, is critical to the cloud evolution. It is demonstrated here, that processes resembling “deep convection” may also be responsible for the cloud development in a marine boundary layer of only 1500 m depth.

Aircraft measurements of ozone, NOx, CO, and aerosol concentrations in biomass burning smoke over Indonesia and Australia in October 1997: Depleted ozone layer at low altitude over Indonesia

The 1997 El Nino unfolded as one of the most sever El Nino Southern Oscillation (ENSO) events in this century and it coincided with massive biomass burning in the equatorial western Pacific region. To assess the influence on the atmosphere, aircraft observations of trace gases and aerosol were conducted over Kalimantan in Indonesia and Australia. Over Kalimantan in Indonesia, high concentrations of O3, NOx, CO, and aerosols were observed during the flight. Although the aerosol and NOx decreased with altitude, the O3 had the maximum concentration (80.5 ppbv) in the middle layer of the smoke haze and recorded very low concentrations (∼20 ppbv) in the lower smoke layer. This feature was not observed in the Australian smoke. We proposed several hypotheses for the low O3 concentration at low levels over Kalimantan. The most likely are lack of solar radiation and losses at the surface of aerosol particles.

Vertical distribution of cloud condensation nuclei concentrations and their effect on microphysical properties of clouds over the sea near the southwest islands of Japan

[1]xa0Aircraft observations were performed over the sea near the southwest islands of Japan under Asian Atmospheric Particulate Environmental Change Experiment 2/Asian Pacific Regional Aerosol Characterization Experiment (APEX-E2/ACE-Asia) project during the period of 16–28 April 2001. The polluted air mass from east Asia was associated with very high concentrations of SO2 (1–10 ppb) and aerosol particles (3000–5000 cm−3) in the marine boundary layer. The cloud condensation nuclei (CCN) concentration at 0.3% supersaturation was as high as 800–2000 cm−3 during the penetrations of air pollutants from east Asia. The correlation coefficient between SO2 and aerosol particles was significant in such polluted atmosphere. Concentration of CCN (NCCN) was linearly related to concentration of aerosol particles (NAP) according to NCCN ∼ 0.75NAP. The ratio of CCN to aerosol condensation nuclei particle concentrations was lower than 0.3 in the relatively clean maritime atmosphere, but it was as high as ∼0.5 in the continentally influenced atmosphere in the boundary layer. These results indicated that the influence of anthropogenic pollutants from east Asia increased the contribution percentage of aerosol particles to CCN in the polluted atmosphere over the observation area. The observational results also indicated that a mean cloud droplet concentration (NC) in the continentally influenced clouds was ∼2 times as much as NC in the relatively clean maritime clouds. The slope of log-log relationship between NC and NCCN was ∼0.39. This study strongly suggests that high CCN concentration formed many cloud droplets and decreased their effective radius at similar liquid water content under the outflow of air pollutants from east Asia.

Number concentration and size distribution of aerosol particles in the middle troposphere over the Western Pacific Ocean

Number concentration and size distribution of aerosol particles were measured on board aircraft during the PACE (Pacific Atmospheric Chemistry Experiment) campaign from Australia to Japan in January 1994. The spatial distribution of condensation nuclei (CN) (r ≥ 4 nm) at 5-6 km altitude showed large variabilities in concentrations from 10 2 to 10 3 mg -1 ; that is, the concentrations were low (70-500 mg -1 ) in the intertropical convergence zone, high (400-1500 mg -1 ) in the subtropical high-pressure area, and low again in the higher latitudes. An apparent opposite tendency was present between CN and large particle (r≥0.15 μm) concentrations. The size distributions in the subtropical region exhibited high number concentrations of very fine particles (r < 0.02 μm). Together with the horizontal observation, vertical observations of aerosols were carried out over some areas. In the subtropical area (Saipan), CN concentration increased with altitude in contrast to the large particle concentration. Also most of the particles collected at 6 km altitude over Saipan contained sulfuric acid. These results are consistent with the results of Clarke (1993, J. geophys. Res. 98,20,633-20,647)that new particle formation is favored in the upper troposphere.

Vertical and latitudinal distributions of tropospheric ozone over the western Pacific: Case studies from the PACE aircraft missions

[1]xa0Three Pacific atmospheric chemistry experiments (PACE I, II, and III) were conducted each in January 1994, October 1994, and July 1995. The objective was to investigate the latitudinal distribution, transportation, and possible sources of tropospheric ozone over the western Pacific. Measurements of ozone using UV absorption method were taken by an aircraft flying at a maximum altitude of 6000 m between the Southern Hemisphere (SH) and the Northern Hemisphere (NH) (38°S–38°N) and within the longitudinal range of 120°E–150°E. The PACE aircraft missions first provide the middle troposphere (5000–6000 m) ozone distributions in three different seasons over this region in relatively short periods of time (within 9 days). On the basis of one-minute average data, ozone mixing ratios in the middle troposphere were significantly higher in the NH midlatitudes (39–92 ppbv) and the SH midlatitudes (30–71 ppbv) than in the tropics (10–35 ppbv) during three different seasons. In particular, an air mass with low ozone mixing ratios (2–28 ppbv) extended from 7°S to 29°N in July during PACE III, in contrast to the air mass with higher ozone mixing ratios (39–57 ppbv) observed in the NH midlatitudes (>21°N) in January during PACE I. Several episodes of increased ozone were observed during the PACE missions. In the SH subtropics (16°S–22°S), photochemical ozone production in a biomass-burning smoke, probably emitted from the northwest part of Australia, caused relatively high ozone mixing ratios (maximum 89 ppbv) at 5200 m during PACE II. In contrast, ozone transport over a long distance from the upper troposphere south of Africa brought about a maximum ozone mixing ratio of 64 ppbv in the same geographical region above 4500 m during PACE III. Large-scale circulation coupled with a typhoon was found to impact ozone transport from the NH midlatitudes to the tropics. An air mass with ozone mixing ratios averaging about 50 ppbv at 5200 m, which originated over the Asian continent in the NH midlatitudes, was transported to the tropical western Pacific region (9°N–14°N) by a circulation coupled with a typhoon during PACE II. Summer observations of tropopause folding over the western Pacific are rare, yet high potential vorticity (PV) value (>1 PV unit) above 600 hPa level at 35°N shows that the tropopause folding beneath the subtropical jet occurred in the NH midlatitudes over the western Pacific in summer during PACE III. In this measurement, the increased ozone (maximum 92 ppbv) combined with decreased water vapor mixing ratio (<3.0 g/kg) and large potential temperature gradient (0.083 K/m) was observed above 3800 m. These facts suggest stratospheric influenced air descended to 3800 m. The source region of the high ozone observed over the tropical region (5°S–9°S) during PACE II has not been confirmed, but it is thought to have originated from biomass burning and might be influenced by circulation associated with El Nino.

Aircraft measurements of tropospheric ozone over the Western Pacific Ocean

Abstract The latitudinal distribution of the tropospheric ozone over the western Pacific Ocean has been observed during two aircraft experiments, namely the 1993 Pre-PACE and the 1994 PACE-I experiments. The ozone concentration in the northern middle latitudes ( > 20°N) was high (40–50 ppbv) and stable in both the experiments, however, the air originating from the Pacific Ocean showed lower concentration of ozone compared to the one that came from the Eurasian Continent. A sharp gradient of the ozone concentration was observed around 10–25°N in these experiments. To the north of this gradient, the air mass with high ozone and low water vapor concentration came from the Eurasian Continent. South of the gradient, the air mass with low ozone and high water vapor concentration came from the tropical Pacific. Extremely low ozone concentrations (as low as 20 ppbv) were observed around the equator during the field experiments. The reason is probably that the ozone was photochemically destroyed by the high water vapor concentration in the boundary layer near the equator and this air mass was lifted up by the Walker circulation. The air mass which came from the middle of Australia showed high concentration of ozone (∼ 50 ppbv) around 20°S on the flight course; on the other hand, the air mass which came from the ocean showed low concentration of ozone around 24°S. The air mass with high concentration of ozone may be affected by mixing with the boundary layer in which photochemical ozone production occurs.