Chemical composition of Asian continental outflow over the western Pacific: Results from Transport and Chemical Evolution over the Pacific (TRACE‐P)

Abstract

We characterize the chemical composition of Asian continental outflow observed during the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) mission during February–April 2001 in the western Pacific using data collected on the NASA DC‐8 aircraft. A significant anthropogenic impact was present in the free troposphere and as far east as 150°E longitude reflecting rapid uplift and transport of continental emissions. Five‐day backward trajectories were utilized to identify five principal Asian source regions of outflow: central, coastal, north‐northwest (NNW), southeast (SE), and west‐southwest (WSW). The maximum mixing ratios for several species, such as CO, C2Cl4, CH3Cl, and hydrocarbons, were more than a factor of 2 larger in the boundary layer of the central and coastal regions due to industrial activity in East Asia. CO was well correlated with C2H2, C2H6, C2Cl4, and CH3Cl at low altitudes in these two regions (r2 ∼ 0.77–0.97). The NNW, WSW, and SE regions were impacted by anthropogenic sources above the boundary layer presumably due to the longer transport distances of air masses to the western Pacific. Frontal and convective lifting of continental emissions was most likely responsible for the high altitude outflow in these three regions. Photochemical processing was influential in each source region resulting in enhanced mixing ratios of O3, PAN, HNO3, H2O2, and CH3OOH. The air masses encountered in all five regions were composed of a complex mixture of photochemically aged air with more recent emissions mixed into the outflow as indicated by enhanced hydrocarbon ratios (C2H2/CO ≥ 3 and C3H8/C2H6 ≥ 0.2). Combustion, industrial activities, and the burning of biofuels and biomass all contributed to the chemical composition of air masses from each source region as demonstrated by the use of C2H2, C2Cl4, and CH3Cl as atmospheric tracers. Mixing ratios of O3, CO, C2H2, C2H6, SO2, and C2Cl4 were compared for the TRACE‐P and PEM‐West B missions. In the more northern regions, O3, CO, and SO2 were higher at low altitudes during TRACE‐P. In general, mixing ratios were fairly similar between the two missions in the southern regions. A comparison between CO/CO2, CO/CH4, C2H6/C3H8, NOx/SO2, and NOy/(SO2 + nss‐SO4) ratios for the five source regions and for the 2000 Asian emissions summary showed very close agreement indicating that Asian emissions were well represented by the TRACE‐P data and the emissions inventory.

Temporal variations of atmospheric CO<sub>2</sub> and CO at Ahmedabad in western India

“…Using CARIBIC observations, Lai et al (2010) also reported the CO / CO 2 ratio in the range of 15.6-29.3 ppb ppm −1 from the air mass influenced by both biofuel and fossil fuel burning in the Indochinese Peninsula. Further, the CO / CO 2 ratio is also observed at about 13 ppb ppm −1 in the south-eastern Asian outflow during February-April 2001 during the TRACE-P cam- paign and it suggests the combined influence of fossil fuel and biofuel burning (Russo et al, 2003). The overall ratios (using all data) from autumn to spring (8.4-12.7 ppb ppm −1 ) suggest the dominance of local emission sources during these seasons, and this range corresponds to the range of anthropogenic combustion sources (10-15 ppb ppm −1 ) in developed countries (Suntharalingam et al, 2004;Takegawa et al, 2004;Wada et al, 2011).…”

Development of a parameterization of black carbon aging for use in general circulation models

“…Note that these initial parameters cover concentrations of chemical species from polluted urban air (e.g., BC = 10.0 µg m −3 and SO 2 = 10.0 parts per billion by volume (ppbv) at the surface in Beijing; Han et al, 2009;Takegawa et al, 2009) to free tropospheric air (e.g., BC = 0.1 µg m −3 and SO 2 = 0.1 ppbv in the free troposphere over the western Pacific; Russo et al, 2003;Oshima et al, 2012). The calculations were conducted using hourly photolysis rates for equinox at midlatitudes, although results obtained in this study can be applied irrespective of latitude and season (see Sects.…”

Free tropospheric peroxyacetyl nitrate (PAN) and ozone at Mount Bachelor: potential causes of variability and timescale for trend detection

“…Aircraft campaigns have shown that variability in the amount of vertical transport out of East Asia impacts the amount of PAN that moves downwind Nowak et al, 2004;Russo et al, 2003). However Liang et al (2005) suggest that transpacific transport is mainly dependent on the meteorology in the eastern half of the Pacific.…”