Kazuyuki Kita

Rapid aerosol particle growth and increase of cloud condensation nucleus activity by secondary aerosol formation and condensation: A case study for regional air pollution in northeastern China

[1] This study was part of the international field measurement Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006). We investigated a new particle formation event in a highly polluted air mass at a regional site south of the megacity Beijing and its impact on the abundance and properties of cloud condensation nuclei (CCN). During the 1-month observation, particle nucleation followed by significant particle growth on a regional scale was observed frequently (~30%), and we chose 23 August 2006 as a representative case study. Secondary aerosol mass was produced continuously, with sulfate, ammonium, and organics as major components. The aerosol mass growth rate was on average 19 μg m -3 h -1 during the late hours of the day. This growth rate was observed several times during the 1-month intensive measurements. The nucleation mode grew very quickly into the size range of CCN, and the CCN size distribution was dominated by the growing nucleation mode (up to 80% of the total CCN number concentration) and not as usual by the accumulation mode. At water vapor supersaturations of 0.07-0.86%, the CCN number concentrations reached maximum values of 4000-19,000 cm -3 only 6-14 h after the nucleation event. During particle formation and growth, the effective hygroscopicity parameter κ increased from about 0.1-0.3 to 0.35-0.5 for particles with diameters of 40-90 nm, but it remained nearly constant at ~0.45 for particles with diameters of ~190 nm. This result is consistent with aerosol chemical composition data, showing a pronounced increase of sulfate.

Tropospheric ozone enhancements during the Indonesian Forest Fire Events in 1994 and in 1997 as revealed by ground‐based observations

Pronounced enhancements of total and tropospheric ozone were observed with the Brewer spectrophotometer and ozonesondes at Watukosek (7.5°S, 112.6°E), Indonesia in 1994 and in 1997 when extensive forest fires were reported in Indonesia. The integrated tropospheric ozone increased from 20 DU to 40 DU in October 1994 and to 55 DU in October 1997. On October 13, 1994, most ozone mixing ratios were more than 50 ppbv throughout the troposphere and exceeded 80 ppbv at some altitudes. On October 22, 1997, the concentrations were more than 50 ppbv throughout the troposphere and exceeded 100 ppbv at several altitudes. The coincidences of the ozone enhancements with the forest fires suggest the photochemical production of tropospheric ozone due to its precursors emitted from the fires for both cases. The years of 1994 and 1997 correspond to El Nino events when convective activity becomes low in Indonesia. Thus, in this region, it is likely that pronounced enhancements of tropospheric ozone associated with extensive forest fires due to sparse precipitation may take place with a period of a few years coinciding with El Nino events. This is in a marked contrast to the situation in South America and Africa where large-scale biomass burnings occur every year.

Stratosphere-troposphere exchange of ozone associated with the equatorial Kelvin wave as observed with ozonesondes and rawinsondes

An intensive observation with ozonesondes and rawinsondes was conducted in Indonesia in May and June 1995 to investigate a phenomenon of ozone enhancement in the tropical upper troposphere. We obtained the characteristics of an enhancement that continued for about 20 days, concurring with a zonal wind oscillation associated with the equatorial Kelvin wave around the tropopause and the Madden-Julian oscillation (MJO) in the troposphere. The isoline of ozone mixing ratio of 40 nmol/mol moved by 5.0 km downward from 17.8 km to 12.8 km, while the tropopause height was 16.2-17.8 km throughout the period. Moreover, the maximum ozone concentration of 300 nmol/mol at the tropopause was concurrent with the maximum eastward wind phase of the Kelvin wave. The detailed mechanism of the ozone transport is interpreted as follows: The downward motion associated with the Kelvin wave and the MJO transported the stratospheric ozone into the troposphere, and the air mixing due to the Kelvin wave breaking at the tropopause also caused stratosphere-troposphere exchange. The upper limit of the net amount of ozone transported from the stratosphere was estimated to be 9.9 Dobson units with the zonal and meridional extents of the ozone-increased region of more than 6.6 × 10 6 m and 1.8 × 10 6 m, respectively, to imply the potential to affect the photochemistry around the tropical tropopause.

Total ozone increase associated with forest fires over the Indonesian region and its relation to the El Niño-Southern oscillation

Significant increases of total ozone were observed both by the total ozone mapping spectrometer (TOMS) and by the Brewer spectrophotometer in Indonesia in September and October of 1994 and 1997, during the El Nino periods, when extensive forest fires were reported in Sumatra Island, Kalimantan (the southern part of Borneo Island) and south New Guinea. The two observations were consistent with each other, and the total ozone increases were attributed to the tropospheric ozone increases because their amplitudes agreed with those of integrated tropospheric ozone increases derived from ozonesonde observations. The TOMS data indicated that the horizontal distributions and temporal variations of the ozone increases were similar in both years; the ozone increases were found mainly over Sumatra Island and the Malay Peninsula in September, and spread out from Kalimantan to the central Indian Ocean in October. This ozone distribution was partly different from the reported fire areas. This difference suggested the importance of the horizontal advection due to the easterly wind in the lower troposphere and of the vertical transport due to the upward wind at the west of Sumatra Island, in the ozone maximum area. Distinctive total ozone increases similar to those in 1994 and 1997 repeatedly appeared over the Indonesian region in the TOMS data between 1979 and 1998. The average ozone increase in this region was estimated by subtracting the background structure of total ozone in the tropics, and this analysis showed that large ozone increases mostly occurred in the dry season during the El Nino periods when the precipitation decreased significantly and extensive forest fires occurred frequently in Indonesia.

Seasonal variation of tropospheric ozone in Indonesia revealed by 5‐year ground‐based observations

Regular ozonesonde observation and total ozone observation with the Brewer spectrophotometer have been conducted at Watukosek (7.5°S, 112.6°E), Indonesia, since 1993. Three seasons are recognized for the vertical distribution of tropospheric ozone. (1) During the local wet season, between December and March, the ozone mixing ratio is nearly constant at 25 ppbv throughout the troposphere. (2) During the transition season from wet to dry, between April and July, the mixing ratio is often enhanced in the uppermost troposphere. (3) During the local dry season, between August and November, the concentration is enhanced in the planetary boundary layer, and extensive forest fires in Indonesia associated with the strong El Nino events of 1994 and of 1997 have enhanced the ozone mixing ratio in the middle troposphere, the integrated tropospheric ozone, and the total ozone at Watukosek.

Vertical and meridional distributions of the atmospheric CO2 mixing ratio between northern midlatitudes and southern subtropics

[1]xa0The atmospheric CO2 mixing ratio was measured using a continuous measurement system onboard a Gulfstream-II aircraft between the northern midlatitudes and the southern subtropics during the Biomass Burning and Lightning Experiment Phase A (BIBLE A) campaign in September–October 1998. The vertical distribution of CO2 over tropical regions was almost constant from the surface to an altitude of 13 km. CO2 enhancements from biomass burning and oceanic release were observed in the tropical boundary layer. Measurements in the upper troposphere indicate interhemispheric exchange was effectively suppressed between 2°N–7°N. Interhemispheric transport of air in the upper troposphere was suppressed effectively in this region. The CO2 mixing ratios in the Northern and Southern Hemispheres were almost constant, with an average value of about 365 parts per million (ppm) and 366 ppm, respectively. The correlation between the CO2 and NOy mixing ratios observed north of 7°N was apparently different from that obtained south of 2°N. This fact strongly supports the result that the north-south boundary in the upper troposphere during BIBLE A was located around 2°N–7°N as the boundary is not necessary a permanent feature.

An assessment of aircraft as a source of particles to the upper troposphere

Condensation nuclei measurements are examined in conjunction with measurements of reactive nitrogen species (NOy) to identify aircraft plumes in primary air traffic corridors over the North Atlantic. Several hundred plumes exhibiting ≥100 pptv enhancements in NOy mixing ratio were observed. The plumes were typically a few hundred meters wide, exhibited high NO/NOy ratios, and ranged in age from ∼10 minutes to ∼10 hours. Assuming the sampled aircraft emitted ∼12 g NOx (as NO2) kg−1 fuel burned and that the loss of NOy to the particle phase was negligible, we calculate median aerosol emission indices in terms of number of particles kg−1 of fuel burned of ∼120×1015 for CN ≥8 nm in size; ∼50×1015 for CN ≥ 17 nm; and ∼3×1015 for the nonvolatile CN ≥ 17 nm. Using published fuel burn statistics, background aerosol concentrations, and a 10 day particle lifetime, we conclude that present aviation sources enhance global averaged upper-tropospheric fine and nonvolatile aerosol number densities by ∼6% and ∼3%, respectively.

Tropospheric ozone behavior observed in Indonesia

Abstract The variation of the surface and free tropospheric ozone has been observed at Watukosek (7.5°S, 112.6°E), Indonesia. This paper is to report the analysis of the ozonesonde data obtained during the period November 1992–June 1994. A seasonal variation of ozone is evident in the lower and middle troposphere, with the maximum occurring in September and October. In the upper troposphere, seasonal variation is not evident, but enhancements were occasionally detected in April, May and June. A common feature that ozone mixing ratio is nearly constant of 20–30 ppbv throughout the troposphere is identified as a basic type of altitude profile appearing in the wet season, December through March, and in the middle of the dry season, July and August. Two other features are occasionally found. One appearing in April, May and June exhibits an enhancement over 50 ppbv in the upper troposphere, and the other appearing in September and October exhibits an enhancement in the lower and middle troposphere.

Photochemical production of ozone in the upper troposphere in association with cumulus convection over Indonesia

[1]xa0The Biomass Burning and Lightning Experiment phase A (BIBLE-A) aircraft observation campaign was conducted from 24 September to 10 October 1998, during a La Nina period. During this campaign, distributions of ozone and its precursors (NO, CO, and nonmethane hydrocarbons (NMHCs)) were observed over the tropical Pacific Ocean, Indonesia, and northern Australia. Mixing ratios of ozone and its precursors were very low at altitudes between 0 and 13.5 km over the tropical Pacific Ocean. The mixing ratios of ozone precursors above 8 km over Indonesia were often significantly higher than those over the tropical Pacific Ocean, even though the prevailing easterlies carried the air from the tropical Pacific Ocean to over Indonesia within several days. For example, median NO and CO mixing ratios in the upper troposphere were 12 parts per trillion (pptv) and 72 parts per billion (ppbv) over the tropical Pacific Ocean and were 83 pptv and 85 ppbv over western Indonesia, respectively. Meteorological analyses and high ethene (C2H4) mixing ratios indicate that the increase of the ozone precursors was caused by active convection over Indonesia through upward transport of polluted air, mixing, and lightning all within the few days prior to observation. Sources of ozone precursors are discussed by comparing correlations of some NMHCs and CH3Cl concentrations with CO between the lower and upper troposphere. Biomass burning in Indonesia was nearly inactive during BIBLE-A and was not a dominant source of the ozone precursors, but urban pollution and lightning contributed importantly to their increases. The increase in ozone precursors raised net ozone production rates over western Indonesia in the upper troposphere, as shown by a photochemical model calculation. However, the ozone mixing ratio (∼20 ppbv) did not increase significantly over Indonesia because photochemical production of ozone did not have sufficient time since the augmentation of ozone precursors. Backward trajectories show that many air masses sampled over the ocean south of Indonesia and over northern Australia passed over western Indonesia 4–9 days prior to being measured. In these air masses the mixing ratios of ozone precursors, except for short-lived species, were similar to those over western Indonesia. In contrast, the ozone mixing ratio was higher by about 10 ppbv than that over Indonesia, indicating that photochemical production of ozone occurred during transport from Indonesia. The average rate of ozone increase (1.8 ppbv/d) during this transport is similar to the net ozone formation rate calculated by the photochemical model. This study shows that active convection over Indonesia carried polluted air upward from the surface and had a discernable influence on the distribution of ozone in the upper troposphere over the Indian Ocean, northern Australia, and the south subtropical Pacific Ocean, combined with NO production by lightning.

Effects of biomass burning, lightning, and convection on O3, CO, and NOyover the tropical Pacific and Australia in August–October 1998 and 1999

[1]xa0In situ aircraft measurements of O3, CO, total reactive nitrogen (NOy), NO, and non-methane hydrocarbons (NMHCs) were made over the western Pacific Ocean and Australia during the Biomass Burning and Lightning Experiment (BIBLE) A and B conducted in August–October 1998 and 1999. Generally, similar features were seen in the BIBLE A and B data in the latitudinal variations of these species in the troposphere from 35°N to 28°S at longitudes of 120°–150°E. The focus of this paper is to describe the characteristics of air masses sampled at 15°N–10°S (tropical Pacific) and 10°S–28°S (over Australia). With the exception of occasional enhancements in reactive nitrogen seen over New Guinea associated with lightning activities, the tropical Pacific region is distinguished from the rest of the region by smaller concentrations of these trace species. This can be explained in terms of the absence of surface sources over the ocean, lack of stratospheric intrusion, and the preclusion of midlatitude air and air from the west due to active convection throughout the troposphere. The median O3, CO, NOy, and NO mixing ratios in tropical air above 4 km were about 15–20 parts per billion by volume (ppbv), 60–75 ppbv, 20–100 parts per trillion by volume (pptv), and 5–40 pptv, respectively. Data obtained from PEM-West A and B conducted in 1991 and 1994 showed similar latitudinal features, although the PEM-West A values were somewhat elevated due to dominating westerly winds in the lower troposphere associated with El Nino. Over Australia, the levels of O3, CO, NOy, NO, and NMHCs were elevated throughout the troposphere over those observed in the tropical Pacific both in 1998 and 1999. The effect from biomass burning that occurred in northern Australia was limited to within the boundary layer because of strong subsidence in the period. Analyses based on 14-day back trajectories identified free tropospheric air over Australia that originated from Indonesia, the Indian Ocean, Africa, and southern midlatitudes. The levels of O3, CO, NOy, and NMHCs in these air masses were much higher than those from the tropical Pacific due to their stronger sources from biomass burning and lightning. These values are compared with those obtained in the South Pacific during PEM-Tropics A. Effects of biomass burning and lightning are discussed as possible sources of O3 and its precursors in these air masses.