Hideki Nara

CO emissions from biomass burning in South-east Asia in the 2006 El Nino year: shipboard and AIRS satellite observations

Environmental context Atmospheric carbon monoxide greatly affects the abundance of environmentally important gases, including methane, hydrochlorofluorocarbons and tropospheric ozone. We present evidence for episodes of CO pollution over the tropical Pacific Ocean resulting from intensive biomass burning in South-east Asia and Northern Australia during the 2006 El Nino year. We discuss the locations of the CO emissions and their long-range transport. Abstract Biomass burning is often associated with climate oscillations. For example, biomass burning in South-east Asia is strongly linked to El Nino–southern oscillation activity. During October and November of the 2006 El Nino year, a substantial increase in CO mixing ratios was detected over the Western tropical Pacific Ocean by shipboard observations routinely operated between Japan and Australia and New Zealand. Combining in-situ measurements, satellite observations, and an air trajectory model simulation, two high CO episodes were identified originating from biomass burning in Borneo, Sumatra, New Guinea, and Northern Australia. Between 15°N and the Equator, marked CO enhancements were encountered associated with a significant correlation between CO and CO2 and between CO and O3. The ΔCO/ΔCO2 ratio observed in the fire plume was considerably high (171 ppbv ppmv–1), suggesting substantial contributions from peat soil burning in Indonesia. In contrast, the ΔO3/ΔCO ratio was only 0.05 ppbv ppbv–1, indicating that net photochemical production of O3 in the plume was negligible during long-range transport in the lower troposphere over the Western tropical North Pacific.

Emissions of methane from offshore oil and gas platforms in Southeast Asia

Methane is a substantial contributor to climate change. It also contributes to maintaining the background levels of tropospheric ozone. Among a variety of CH4 sources, current estimates suggest that CH4 emissions from oil and gas processes account for approximately 20% of worldwide anthropogenic emissions. Here, we report on observational evidence of CH4 emissions from offshore oil and gas platforms in Southeast Asia, detected by a highly time-resolved spectroscopic monitoring technique deployed onboard cargo ships of opportunity. We often encountered CH4 plumes originating from operational flaring/venting and fugitive emissions off the coast of the Malay Peninsula and Borneo. Using night-light imagery from satellites, we discovered more offshore platforms in this region than are accounted for in the emission inventory. Our results demonstrate that current knowledge regarding CH4 emissions from offshore platforms in Southeast Asia has considerable uncertainty and therefore, emission inventories used for modeling and assessment need to be re-examined.

Emission factors of CO2, CO and CH4 from Sumatran peatland fires in 2013 based on shipboard measurements

Abstract We observed prominent CO enhancements with simultaneous enhancements of CO2 and CH4 around the Malay Peninsula in South-East Asia from mid-June to mid-August 2013 based on systematic shipboard observations. We identified 18 episodes of CO enhancement during the period, which were responsible for the largest positive anomaly of CO observed in the areas of off the eastern coast of Peninsular Malaysia and in the Straits of Malacca between 2007 and 2013 based on shipboard observations. Satellite data revealed that the CO enhancements resulted mainly from the emissions from large-scale biomass burning in north-central Sumatra. We characterized five biomass burning peaks with strong fire emission signatures based on the relationship between CO2 and CO. From these peaks, we estimated the average emission factors (EFs) for CO2, CO and CH4 from the fires in the study area. The estimated average EFs for CO2 and CO agreed well with those predicted by version 4.1s of the Global Fire Emissions Database (GFED4.1s) using the recommended EF values, but the CH4 EF differed substantially, suggesting high uncertainty of the CH4 EF for peat in GFED4.1s. We estimated the typical EF values for peat fires based on the average EF values from the present study. The estimated typical EF values were 1663 ± 54 g/kg for CO2, 205 ± 23 g/kg for CO and 7.6 ± 1.6 g/kg for CH4. Despite the lack of a clear difference for CO2 and CO, our estimated typical EF of CH4 was less than half of the GFED4.1s-recommended EF and was comparable to previously reported EF values for Borneo peat. These results suggest a significant overestimation of the EF of CH4 for peat fires in GFED4.1s; using the present values would greatly decrease the estimated contribution of Equatorial Asia to global fire emissions of CH4, especially in drought years.