S. Kawakami

Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology 1. Comparison with Total Ozone Mapping Spectrometer (TOMS) and ground-based measurements

[1]xa0A network of 10 southern hemisphere tropical and subtropical stations, designated the Southern Hemisphere Additional Ozonesondes (SHADOZ) project and established from operational sites, provided over 1000 ozone profiles during the period 1998–2000. Balloon-borne electrochemical concentration cell (ECC) ozonesondes, combined with standard radiosondes for pressure, temperature, and relative humidity measurements, collected profiles in the troposphere and lower to midstratosphere at: Ascension Island; Nairobi, Kenya; Irene, South Africa; Reunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristobal, Galapagos; and Natal, Brazil. The archived data are available at: 〈http://croc.gsfc.nasa.gov/shadoz〉.1 In this paper, uncertainties and accuracies within the SHADOZ ozone data set are evaluated by analyzing: (1) imprecisions in profiles and in methods of extrapolating ozone above balloon burst; (2) comparisons of column-integrated total ozone from sondes with total ozone from the Earth-Probe/Total Ozone Mapping Spectrometer (TOMS) satellite and ground-based instruments; and (3) possible biases from station to station due to variations in ozonesonde characteristics. The key results are the following: (1) Ozonesonde precision is 5%. (2) Integrated total ozone column amounts from the sondes are usually to within 5% of independent measurements from ground-based instruments at five SHADOZ sites and overpass measurements from the TOMS satellite (version 7 data). (3) Systematic variations in TOMS-sonde offsets and in ground-based-sonde offsets from station to station reflect biases in sonde technique as well as in satellite retrieval. Discrepancies are present in both stratospheric and tropospheric ozone. (4) There is evidence for a zonal wave-one pattern in total and tropospheric ozone, but not in stratospheric ozone.

Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology 2. Tropospheric variability and the zonal wave-one

(1) The first view of stratospheric and tropospheric ozone variability in the Southern Hemisphere tropics is provided by a 3-year record of ozone soundings from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network (http://croc.gsfc.nasa.gov/ shadoz). Observations covering 1998-2000 were made over Ascension Island, Nairobi (Kenya), Irene (South Africa), Reunion Island, Watukosek (Java), Fiji, Tahiti, American Samoa, San Cristobal (Galapagos), and Natal (Brazil). Total, stratospheric, and tropospheric column ozone amounts usually peak between August and November. Other features are a persistent zonal wave-one pattern in total column ozone and signatures of the quasi-biennial oscillation (QBO) in stratospheric ozone. The wave-one is due to a greater concentration of free tropospheric ozone over the tropical Atlantic than the Pacific and appears to be associated with tropical general circulation and seasonal pollution from biomass burning. Tropospheric ozone over the Indian and Pacific Oceans displays influences of the waning 1997-1998 El Nino, seasonal convection, and pollution transport from Africa. The most distinctive feature of SHADOZ tropospheric ozone is variability in the data, e.g., a factor of 3 in column amount at 8 of 10 stations. Seasonal and monthly means may not be robust quantities because statistics are frequently not Gaussian even at sites that are always in tropical air. Models and satellite retrievals should be evaluated on their capability for reproducing tropospheric variability and fine structure. A 1999- 2000 ozone record from Paramaribo, Surinam (6� N, 55� W) (also in SHADOZ) shows a marked contrast to southern tropical ozone because Surinam is often north of the Intertropical Convergence Zone (ITCZ). A more representative tropospheric ozone climatology for models and satellite retrievals requires additional Northern Hemisphere tropical data. INDEXTERMS: 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 1640 Global Change: Remote sensing; 3309 Meteorology and Atmospheric Dynamics: Climatology (1620); 9305 Information Related to Geographic Region: Africa; 9325 Information Related to Geographic Region: Atlantic Ocean; KEYWORDS: Free-words-ozone, tropospheric ozone, ozonesondes, satellite ozone, tropical climatology, wave-one, biomass burning, El Nino, satellite retrievals

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.

Profiles and partitioning of reactive nitrogen over the Pacific Ocean in winter and early spring

Measurements of NO, NO y , PAN, HNO 3 , O 3 , CO, CH 4 , nonmethane hydrocarbons (NMHCs), and H 2 O were made over the Pacific Ocean in February and March during the Pacific Exploratory Mission West B (PEM-West B). NO x was calculated from NO using a photochemical model. These data were classified according to six air mass categories: western Pacific maritime, tropical, tropical convective, western Pacific continental, high latitude, and stratospheric. It has been found that the mixing ratios of many of the observed species and partitioning of NO varied significantly depending on altitude, air mass, and season. These variations have been interpreted in terms of chemical and transport processes. In the maritime air below 7 km, the mixing ratios of calculated NO x ((NO x ) mc ), PAN, and NO were lower than those in the continental air masses. The lowest values of PAN, HNO 3 , NO y , and O 3 were observed in the tropical region below 5 km. In the continental air, NO y , PAN, CO, and NMHC levels below 4 km were much higher than those obtained in September and October during PEM-West A, due to rapid transport of these species from anthropogenic sources on the continent to the Pacific Ocean by the westerly winds which dominated in early winter and spring. Reduced photochemistry during winter also contributed to the higher values of CO and NMHCs. Above 7 km the values of these species were lower during PEM-West B, possibly due to much weaker convective activity in early spring. In spite of the weaker vertical transport, the median values of (NO x ) mc and the (NO x ) mc /C 3 H 8 ratio at 10 km were 110-140 parts per trillion by volume (pptv) and 2.9-3.4 pptv/pptv, respectively, in the continental and maritime air masses, indicating the importance of in situ NO x production in the upper troposphere. In the continental air the PAN/NO y and HNO 3 /N y ratios ranged between 0.2 and 0.5, showing clear anticorrelation. The PAN/NO y ratio was also anticorrelated with the temperature. In the high-latitude air between 1 and 7 km the PAN/NO y ratio was 0.5-0.8, and the (NO x ) mc /NO y ratio was less than 0.05. Temperature and the concentrations of OH and NMHCs are considered to have strongly influenced the partitioning of NO y at middle and high latitudes. Generally, the sum of (NO x ) mc , PAN, and HNO 3 constituted 90 ± 10% of the observed NO from the boundary layer up to 7 km in all types of air masses. This finding improves our basic understanding on the chemistry and budget of the reactive nitrogen.

Performance of an aircraft instrument for the measurement of NO y

Measurements of NO and NOy using a chemiluminescence technique were made on board a DC-8 aircraft during NASAs Pacific Exploratory Mission-West B (PEM-West B). The gold converter to convert NOy species into NO was operated at a constant pressure using a servo-controlled Teflon valve, which has been used for NOy measurements on board the ER-2 aircraft. The results of laboratory tests and some flight data during PEM-West B are presented. These experiments indicate no detectable inlet loss of HNO3 in dry air, although some loss was observed at H2O mixing ratios of 1–2%. The laboratory tests also showed small variability in the NOy artifact, high conversion efficiency for NO2 and HNO3, low HCN conversion efficiency, good repeatability of the measurements, and fast response. The control of the converter pressure during flight has been proven to be very advantageous in making reliable aircraft NOy measurements in the troposphere. The uncertainties of the NO and NOy PEM-West B data, including the effects of HCN conversion and HNO3 inlet loss, have been estimated.

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.

Reactive nitrogen over the Pacific Ocean during PEM-West A

Measurements of NO and NO y were carried out during NASAs Pacific Exploratory Mission-West A. In total, 18 aircraft flights were made over the Pacific Ocean, predominantly over the western Pacific Ocean in September and October 1991. NO and NO were measured using a chemiluminescence instrument, and NO x was calculated from NO using a chemical box model. The measurements were carried out from 0.3 to 12 km in altitude. The NO, calculated NO x ((NO x ) mc ), and NO y mixing ratios in continental air were significantly higher than in maritime air. In maritime air, NO increased with altitude. The median values of NO in the boundary layer and the lower, middle, and upper troposphere were 3.7, 5.1, 11.5, and 26.6 parts per trillion by volume (pptv), respectively. In continental air, NO and (NO x ) mc mixing ratios revealed a C-shaped profile. The median NO values observed in the four altitude regions were 37.8, 17.5, 18.2, and 53.2 pptv, respectively. NO did not show any apparent altitude dependence either in maritime or in continental air. In maritime air, median NO y values in the lower, middle, and upper troposphere ranged between 211 and 226 pptv and in continental air between 382 and 401 pptv. The lowest values of NO y , PAN, and O 3 were observed in tropical air masses throughout the entire altitude region. In the middle and upper troposphere of the high-latitude air masses, NO and (NO x ) mc values were the lowest, although NO y mixing ratios were similar to those in continental air masses. PAN, O 3 , CO, CH 4 , and C 2 H 6 data were used to study the budget of reactive nitrogen over the Pacific Ocean. O 3 mixing ratios were found to be correlated with those of (NO x ) mc , NO y , PAN, and CH 4 , although the degree of correlation varied with air mass and altitude. These correlations, together with the profiles of these species, suggest that photochemical production of O 3 from precursor species over the continent is important for the O 3 budget in the troposphere over the western Pacific Ocean.

Emission estimates of selected volatile organic compounds from tropical savanna burning in northern Australia

[i] Here we present measurements of a range of carbon-based compounds: carbon dioxide (CO 2 ), carbon monoxide (CO), methane (CH 4 ), nonmethane hydrocarbons (NMHCs), methyl halides, and dimethyl sulfide (DMS) emitted by Australian savanna fires studied as part of the Biomass Burning and Lightning Experiment (BIBLE) phase B aircraft campaign, which took place during the local late dry season (28 August to 13 September 1999). Significant enhancements of short-lived NMHCs were observed in the boundary layer (BL) over the region of intensive fires and indicate recent emissions for which the mean transport time was estimated to be about 9 hours. Emission ratios relative to CO were determined for 20 NMHCs, 3 methyl halides, DMS, and CH 4 based on the BL enhancements in the source region. Tight correlations with CO were obtained for most of those compounds, indicating the homogeneity of the local savanna source. The emission ratios were in good agreement with some previous measurements of savanna fires for stable compounds but indicated the decay of emission ratios during transport for several reactive compounds. Based on the observed emission ratios, emission factors were derived and compared to previous studies. While emission factors (g species/kg dry mole) of CO 2 varied little according to the vegetation types, those of CO and NMHCs varied significantly. Higher combustion efficiency and a lower emission factor for methane in this study, compared to forest fires, agreed well with results for savanna fires in other tropical regions. The amount of biomass burned was estimated by modeling methods using available satellite data, and showed that 1999 was an above average year for savanna burning. The gross emissions of the trace gases from Australian savanna fires were estimated.

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.

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.