Convergent evidence for the pervasive but limited contribution of biomass burning to atmospheric ammonia in peninsular Southeast Asia

( )Ammonia (NH3) is an important agent involved in atmospheric chemistry and nitrogen cycling. Current estimates of NH3 emissions from biomass burning (BB) differ by more than a factor of 2, impeding a reliable assessment of their environmental consequences. Combining high-resolution satellite observations of NH3 columns with network measurements of the concentration and stable nitrogen isotope composition (delta N-15) of NH3, we present coherent estimates of the amount of NH3 derived from BB in the heart-land of Southeast Asia, a tropical monsoon environment. Our results reveal a strong variability in atmospheric NH3 levels in time and space across different landscapes. All of the evidence on hand suggests that anthropogenic activities are the most important modulating control with respect to the observed patterns of NH3 distribution in the study area. N-isotope balance considerations revealed that during the intensive fire period, the atmospheric input from BB accounts for no more than 21 +/- 5 % (1 sigma) of the ambient NH3, even at the rural sites and in the proximity of burning areas. Our N-isotope-based assessment of the variation in the relative contribution of BB-derived NH3 is further validated independently through the measurements of particulate K+, a chemical tracer of BB. Our findings underscore that BB-induced NH3 emissions in tropical monsoon environments can be much lower than previously anticipated, with important im- plications for future modeling studies to better constrain the climate and air quality effects of wildfires.

Automated summary

This study combines satellite observations and network measurements to estimate NH3 emissions from biomass burning in Southeast Asia, revealing strong variability in atmospheric NH3 levels across different landscapes. The findings suggest that anthropogenic activities are the primary modulating control factor for NH3 distribution in the region.