Long-term and Seasonal Trends of OMI-derived Tropospheric Column NO2 in Southeast Asia: Urban Emissions, Seasonal Burning, and the Influence of Meteorology

Abstract:

As the Southeast Asia (SEA) region hosts a number of developing countries, several of which practice agricultural burning, understanding both urban and burning-related sources of NO2 is essential for pollution mitigation strategies in these countries. This study utilizes tropospheric NO2 column values from the Ozone Monitoring Instrument (OMI) to identify long-term, seasonal, and spatial trends at selected cities across the SEA region for the period January 2005 to December 2016. Regional hotspots of NO2 column values were observed over Bangkok, Singapore, and Jakarta; however, considerable values were also observed from burning sites. Long-term analysis showed varied relative trends such as +4.5% year-1 in Hanoi and -5.1% year-1 in Jakarta. A general long-term increase in Northern SEA (1.8% year-1) and a slight decrease in Southern SEA (-0.08% year-1) are noted. A comparison of spatial patterns in 2016 and 2005 show significant increase in NO2 column values over several burning areas in Northern SEA. The correlation analysis with meteorology shows that rainfall, boundary layer height, and surface solar radiation were the most influential environmental factors overall, showing strong correlations with statistical significance at the p = 0.05 level across multiple cities; however, slight variations in the most important environmental factors per city were observed. Strong correlations with fire radiative power and fire count existed in cities near burning sites, indicating the important NO2 contribution of local- to regional-scale burning, while other cities showed weak correlations with nearly all environmental variables, indicating the dominant role of their own urban emissions. Both wind speed and wind direction were found to be important in modulating NO2 columns which highlights the role of long-range transport in the advection of emissions across SEA from burning areas to cities, and vice-versa. Further work will extend the analysis until December 2019.