Isotopic Constraints on the Atmospheric Sources and Formation of Nitrogenous Species in Biomass-Burning-Influenced Clouds

Abstract

The interpretation of tropospheric cloud formation rests on understanding the sources and processes affecting aerosol constituents of the atmosphere that are preserved in cloudwater. 25 However, this challenge is difficult to be quantitatively addressed based on the sole use of bulk chemical properties. Nitrogenous aerosols, mainly ammonium (NH4 + ) and nitrate (NO3 -), play an important role in tropospheric cloud formation. Here we collected cloudwater samples at the summit of Mt. Tai (1545 m above sea level) in Eastern China during a long-lasting biomass burning (BB) event, and measured for the first time the isotopic compositions (mean ± 1σ) of 30 cloudwater nitrogen species (δ 15 N-NH4 + = -6.53 ± 4.96‰, δ 15 N-NO3 -= -2.35 ± 2.00‰, δ 18 O-NO3 -= 57.80 ± 4.23‰), allowing insights into their sources and potential transformation mechanism within the clouds. Large contributions of BB to the cloudwater NH4 + (32.9 ± 4.6%) and NO3 -(28.2 ± 2.7%) inventories were confirmed through a Bayesian isotopic mixing model, coupled with our newly-developed computational quantum chemistry module. Despite an overall reduction in total 35 anthropogenic NOx emission due to effective emission control actions and stricter emission standards for vehicles, the observed cloud δ 15 N-NO3values suggest that NOx emissions from transportation may have exceeded emissions from coal combustion. δ 18 O-NO3values imply that the reaction of OH with NO2 is the dominant pathway of NO3formation (57 ± 11%), yet the Atmos. Chem. Phys. Discuss., https://doi.

The evolution of cloud microphysics upon aerosol interaction at the summit of Mt. Tai, China

“…Tai is far away from anthropogenic emission sources on the ground. But high concentrations of inorganic 15 ions in PM2.5 (Zhou et al, 2009), abundant bacterial communities , NH3 and NOx emissions form biomass burning (Chang et al, 2018) have been observed at the summit, thus one infers a strong anthropogenic influence. Previous studies of cloud samples collected at the same position showed high inorganic ion concentrations (Li et al, 2017a;Wang et al, 2011), which can be attributable to the perturbation of anthropogenic aerosol.…”