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

摘要: Abstract Ozone (O 3 ) is an important ground-level pollutant. O levels and emissions of precursors have increased significantly over recent decades in East Asia export this eastward across the Pacific Ocean well documented. Here we show that Asian also transported southward to tropical Southeast (SE) during Northeast Monsoon (NEM) season (defined as November February), transport pathway especially strong ‘cold surges’. Our analysis employs reanalysis data measurements from surface sites Peninsular Malaysia, both covering 2003–2012, along with trajectory calculations. Using a cold surge index (northerly winds at 925 hPa averaged 105–110°E, 5°N) define sub-seasonal strengthening NEM winds, find largest changes region much Indochinese Peninsula surrounding seas. Here, another key pollutant, carbon monoxide, calculated by Monitoring Atmospheric Composition Climate (MACC) Reanalysis are on average elevated by, respectively, >40% (∼15 ppb) >60% (∼80 ppb) surges. Further, broader SE local afternoon exceedances World Health Organization's air quality guideline for (100 μg m −3 , or ∼50 ppb, 8 h) largely occur these Day-to-day variations available observations east coast Malaysia corresponding parts MACC similar, clearly linked However, observed typically ∼10–20 ppb lower than Reanalysis. We subject influence urban pollution. In agreement past work, year-to-year activity related El Nino-Southern Oscillation (ENSO), but does not appear be dominant ENSO atmospheric composition region. Overall, our study indicates pollution could least large corresponding, well-studied spring-time North America. Both enhanced regional observational capability chemical modelling studies will required fully untangle importance long-range relative processes.