[1] Measurements of gaseous and particulate reactive nitrogen and sulfur species, as well as other chemical species, were made using the P-3B and DC-8 aircraft over the western Pacific during the NASA Transport and Chemical Evolution over the Pacific (TRACE-P) experiment, conducted between February and April 2001. These measurements provide a good opportunity to study the extent to which anthropogenic NO x and SO 2 emitted over the East Asian countries remain as NO y and SO x (=SO 2 + nssSO 4 2À) in the form of gas or fine particles when an air mass is transported into the western Pacific region. In this paper a method to estimate transport efficiencies, e(NO y ) and e(SO x ), in an air mass that has experienced multiple injection, mixing, and loss processes is described. In this analysis, CO and CO 2 are used as passive tracers of transport, and the emission inventories of CO, CO 2 , NO x , and SO 2 over the East Asia region are used. Results from the P-3B presented in this study indicate that 20-40% and 15% of NO x emitted over the northeastern part of China remained as NO y over the western Pacific in the boundary layer (BL) and free troposphere (FT), respectively. In the FT, PAN is found to have been the dominant form of NO y , while only 0.5% of emitted NO x remained as NO x . The transport efficiency of SO x is estimated to have been 25-45% and 15-20% in the BL and FT, respectively. Median values of the nssSO 4 2À /SO x ratio are 0.4-0.6 both in the BL and FT, however large variability is found in the FT. These results are generally consistent with those derived using DC-8 data. The results obtained in this study indicate that more than half of NO y and SO x were lost over the continent and that the vertical transport from the BL to FT further reduced their amounts by a factor of 2, likely due to wet removal. Budgets of NO y and SO x were also studied for air masses, which we sampled during TRACE-P and the flux out from the continent in these cases is estimated to be 20% of the emissions. Flux in the BL and FT is found to have a similar contribution.
In situ aircraft measurements of ozone (O3) and its precursors were made over northern Australia in August–September 1999 during the Biomass Burning and Lightning Experiment Phase B (BIBLE‐B). A clear positive correlation of O3 with carbon monoxide (CO) was found in biomass burning plumes in the boundary layer (<3 km). The ΔO3/ΔCO ratio (linear regression slope of O3‐CO correlation) is found to be 0.12 ppbv/ppbv, which is comparable to the ratio of 0.15 ppbv/ppbv observed at 0–4 km over the Amazon and Africa in previous studies. The net flux of O3 exported from northern Australia during BIBLE‐B is estimated to be 0.3 Gmol O3/day. In the biomass burning region, large enhancements of O3 were coincident with the locations of biomass burning hot spots, suggesting that major O3 production occurred near fires (horizontal scale <50 km).
[1] The Biomass Burning and Lightning Experiment phase A (BIBLE A) aircraft campaign was carried out over the tropical western Pacific in September and October 1998. During this period, biomass burning activity in Indonesia was quite weak. Mixing ratios of NO x and NO y in air masses that had crossed over the Indonesian islands within 3 days prior to the measurement (Indonesian air masses) were systematically higher than those in air masses originating from the central Pacific (tropical air masses). Sixty percent of the Indonesian air masses at 9-13 km (upper troposphere, UT) originated from the central Pacific. The differences in NO y mixing ratio between these two types of air masses were likely due to processes that occurred while air masses were over the Islands. Evidence presented in this paper suggests convection carries material from the surface, and NO is produced from lightning. At altitudes below 3 km (lower troposphere, LT), typical gradient of NO x and NO y to CO (dNO y /dCO and dNO x /dCO) was smaller than that in the biomass burning plumes and in urban areas, suggesting that neither source has a dominant influence. When the CO-NO x and CO-NO y relationships in the UT are compared to the reference relationships chosen for the LT, the NO x and NO y values are higher by 40-60 pptv (80% of NO x ) and 70-100 pptv (50% of NO y ). This difference is attributed to in situ production of NO by lightning. Analyses using air mass trajectories and geostationary meteorological satellite (GMS) derived cloud height data show that convection over land, which could be accompanied by lightning activity, increases the NO x values, while convection over the ocean generally lowers the NO x level. These processes are found to have a significant impact on the O 3 production rate over the tropical western Pacific.
The Biomass Burning and Lightning Experiment phase C (BIBLE‐C) aircraft mission was carried out near Darwin, Australia (12°S, 131°E) in December 2000. This was the first aircraft experiment designed to estimate lightning NO production rates in the tropics, where production is considered to be most intense. During the two flights (flights 10 and 13 made on December 9 and 11–12, respectively) enhancements of NOx (NO + NO2) up to 1000 and 1600 parts per trillion by volume (pptv, 10‐s data) were observed at altitudes between 11.5 and 14 km. The Geostationary Meteorological Satellite (GMS) cloud (brightness temperature) data and ground‐based lightning measurements by the Global Positioning and Tracking System (GPATS) indicate that there were intensive lightning events over the coast of the Gulf of Carpentaria, which took place upstream from our measurement area 10 to 14 h prior to the measurements. For these two flights, air in which NOx exceeded 100 pptv extended over 620 × 140 and 400 × 170 km2 (wind direction × perpendicular direction), respectively, suggesting a significant impact of lightning NO production on NOx levels in the tropics. We estimate the amount of NOx observed between 11.5 and 14 km produced by the thunderstorms to be 3.3 and 1.8 × 1029 NO molecules for flights 10 and 13, respectively. By using the GPATS lightning flash count data, column NO production rates are estimated to be 1.9–4.4 and 21–49 × 1025 NO molecules per single flash for these two flight data sets. In these estimations, it is assumed that the column NO production between 0 and 16 km is greater than the observed values between 11.5 and 14 km by a factor of 3.2, which is derived using results reported by Pickering et al. (1998). There are however large uncertainties in the GPATS lightning data in this study and care must be made when the production rates are referred. Uncertainties in these estimates are discussed. The impact on the ozone production rate is also described.
[1] The seasonal variation of ozone (O 3 ) in the boundary layer (BL) over the western Pacific is investigated using a chemistry-transport model. The model results for January and April-May 2002 were evaluated by comparison with PEACE aircraft observations. In January, strong northwesterlies efficiently transported NO x from the continent, leading to an O 3 increase of approximately 5-10 ppbv over a distance of about 3000 km. In April, southwesterlies dominated due to anticyclone development over the western Pacific. Along this flow, O 3 continued to be produced by NO x emitted from East Asia. This resulted in the formation of a high-O 3 (> 50 ppbv) region extending along the coastal areas of East Asia. This seasonal change in O 3 was driven in part by a change in the net O 3 production rate due to increases in solar UV and H 2 O. Its exact response depended on the NO x values in the BL. The net O 3 production rate increased between winter and spring over the Asian continent and decreased over the remote western Pacific. Model simulations show that about 25% of the total O 3 (of 10-20 ppbv) increase over the coastal region of Northeast Asia was due to local production from NO x emissions from China, and the rest was due to changes in background levels as well as emissions from Korea, Japan, and east Siberia. Uplift of BL air over Asia, horizontal transport in the free troposphere, and subsidence were the principal mechanisms of transporting Asian O 3 to the central and eastern North Pacific.Citation: Kondo, Y., et al. (2008), Mechanisms that influence the formation of high-ozone regions in the boundary layer downwind of the Asian continent in winter and spring,
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