Influence of Northeast Monsoon cold surges on air quality in Southeast Asia

Abstract

15Ozone (O3) is an important ground-level pollutant. O3 levels and emissions of O3 precursors have 16 increased significantly over recent decades in East Asia and export of this O3 eastward across the 17 Pacific Ocean is well documented. Here we show that East Asian O3 is also transported southward to 18 tropical Southeast (SE) Asia during the Northeast Monsoon (NEM) season (defined as November to 19 February), and that this transport pathway is especially strong during 'cold surges'. Our analysis 20 employs reanalysis data and measurements from surface sites in Peninsular Malaysia, both covering 21 2003-2012, along with trajectory calculations. Using a cold surge index (northerly winds at 925 hPa 22 averaged over 105-110°E, 5°N) to define sub-seasonal strengthening of the NEM winds, we find the 23 largest changes in a region covering much of the Indochinese Peninsular and surrounding seas. Here, 24 the levels of O3 and another key pollutant, carbon monoxide, calculated by the Monitoring 25

Haze in Singapore – source attribution of biomass burning PM<sub>10</sub> from Southeast Asia

“…Previous studies have shown the importance of ENSO in relation to reduction in convection and precipitation over the Martime Continent (MC) and corresponding increase in haze in Southeast Asia (Ashfold et al, 2017;Inness et al, 2015;Reid et al, 2012). The ENSO conditions have varied significantly during the 6-year period of our study (2010)(2011)(2012)(2013)(2014)(2015).…”

“…The weather and climate in Singapore and hence the transport of smoke from biomass burning are dominated by monsoon periods and influenced by the variations of the El Niño-Southern Oscillation (ENSO), which modifies temperatures in the central equatorial pacific (Ashok et al, 2007;Yeh et al, 2009;Reid et al, 2012;Yuan and Yang, 2012). Meteorologically, the year in Singapore is split into four seasons, with two monsoon seasons separated by two inter-monsoon seasons.…”

Chemical characterisation of water-soluble ions in atmospheric particulate matter on the east coast of Peninsular Malaysia

“…Whilst the meteorological data from the Airport will not be exactly representative of the measurement site, the patterns in wind direction are consistent with observations made by the field scientists during the campaign. In addition, during a study of the influence of northeast monsoon cold surges on air quality in Southeast Asia, Ashfold et al (2017) used meteorological data from three locations that they believed to lie in the path of cold surges during the northeast monsoon, offering the best possibility of observing a cold-surge influence on air pollution. These sites were in Kota Bharu (lat 6.141, long.…”

“…For example, high photochemical activity in these regions means that global atmospheric lifetimes of key atmospheric species, such as methane and ozone, are controlled by destruction rates in the tropics (Lawrence et al, 2001;Bloss et al, 2005). In terms of ocean productivity, the observed decrease in primary productivity in low-latitude oceans has been linked to a reduced availability of nutrients for phytoplankton growth, caused by changes in upper-ocean temperature and stratification (Behrenfeld et al, 2006). Furthermore, the wind circulation system in the Maritime Continent is influenced by seasonal Asian monsoons, which are controlled by the natural oscillation of the intertropical convergence zone (ITCZ).…”

Impact of sea ice decline in the Arctic Ocean on the number of extreme low‐temperature days over China

“…Various studies have focused on trends in the number of extreme low‐temperature days (NELD) and extreme low temperatures; many studies have shown that the NELD has a decreasing trend and that the values of low‐temperature extremes have been increasing on global and regional scales in the past decade (Alexander et al ., ; Griffiths and Bradley, ; Jakob and Walland, ; Ashfold et al ., ; Salman et al ., ; Zhong et al ., ). Some studies have predicted future changes in the NELD through different models, and most results have revealed that the NELD would decrease and the extreme low temperatures would become warmer (Easterling et al ., ; Saha et al ., ; Fonseca et al ., ).…”