Aircraft observations of dust and pollutants over northeast China: Insight into the meteorological mechanisms of transport

Abstract

[1] The meteorological mechanisms for lofting trace gases and aerosols out of the planetary boundary layer (PBL) into the free troposphere are key to understanding local air pollution problems as well as regional and global atmospheric chemistry and climate issues. Over the North American continent, convective storms and lifting in warm conveyor belts transport pollutants into the free troposphere. Little is known about the vertical distribution of pollutants and dust over east Asia, and the processes leading to transport, transformation, and removal of these species remain uncertain. To provide insight into these mechanisms, we report on eight flights based out of Shenyang in NE China as part of the U.S./China EAST-AIRE project conducted in April 2005. We evaluate profiles of trace species, along with back trajectories and satellite data, in the meteorological context of cyclonic systems. The warm-sector PBL air ahead of a cold front was highly polluted, while in the free troposphere concentrations of trace gases and aerosols were lower, but well above background; we measured $300 ppb CO, $2 ppb SO 2 , $70 ppb O 3 , and $ 8 Â 10 À5 m À1 aerosol scattering between $1000 and 4000 m altitude. Satellite observations indicate that the entire plume contained almost 10 5 tons of SO 2 and that the gas decayed with a lifetime of 3-5 d. Roughly the same mass of aerosol was transported into the free troposphere. Over the east Asian continent, dry convection appears to dominate with warm conveyor belts first coming into play as the cyclonic systems move off the coast.

Recent large reduction in sulfur dioxide emissions from Chinese power plants observed by the Ozone Monitoring Instrument

“…A recent study [Lee et al, 2009] applying GEOS-Chem simulated SO 2 and aerosol profiles suggests a seasonal average AMF of ∼0.5 over China. Validation against aircraft measurements over China [Dickerson et al, 2007;Xue et al, 2010] has shown that the operational OMI PBL SO 2 product can distinguish between clean and polluted conditions [Krotkov et al, 2008].…”

Impact of Asian dust and continental pollutants on cloud chemistry observed in northern Taiwan during the experimental period of ABC/EAREX 2005

“…Asian mineral dust can be transported by the prevailing westerlies in the spring [e.g., Zhang et al, 1997], increasing particulate matter concentrations [e.g., Liu et al, 2006;Park et al, 2008] and pH values of rainwater [Wang et al, 2002] and cloud water in downwind areas. Aircraft observations through Asian outflow over the Asian continent [Dickerson et al, 2007] and the northwest Pacific Jordan et al, 2003;Maxwell-Meier et al, 2004], and in transpacific Asian plumes over the northeast Pacific [Andreae et al, 1988;Clarke et al, 2001;Price et al, 2003], have provided evidence of aerosol transport in the lower free troposphere. They reveal the spring months to be the time of maximum trans-Pacific transport of outflow and anthropogenic emissions associated with Asian dust, resulting in combined dust and pollution signatures in measurements of nominal air mass characteristics.…”

Evidence of stratosphere–troposphere exchange during severe cyclones: a case study over Bay of Bengal, India

“…The physical processes behind the transport of gases from the planetary boundary layer into the free troposphere are crucial towards understanding air pollution problems at local and global scales as well as climate issues (Lelieveld and Crutzen 1990;Fadnavis et al 2011). Dickerson et al (2007) showed the role of cyclone in transporting pollutants into the UT from lower troposphere (LT) and reported the vertical exchange of ozone from lower stratosphere to UT. The tropopause height (TH) is also an important meteorological parameter that separates the troposphere from the stratosphere (Wirth 2001).…”