Abstract View
Synergistic Particle Formation in the Upper Troposphere by Nitric Acid, Sulfuric Acid, and Ammonia
MINGYI WANG, The CLOUD Collaboration, Neil Donahue, Carnegie Mellon University
Abstract Number: 432
Working Group: Aerosols, Clouds and Climate
Abstract
New particle formation in the free troposphere is a major global source of cloud condensation nuclei (CCN). But it remains ambiguous what precursor vapors drive the process in the relatively cold upper troposphere, especially over the tropical convective regions where abundant newly-formed particles have been consistently observed. With experiments performed in the CLOUD chamber at CERN with nitric acid, sulfuric acid, and ammonia levels as well as temperatures characteristic of the upper troposphere, we show that this multicomponent system forms particles synergistically, with formation rates orders of magnitude higher than those from any two of the three components. Particle formation may be ammonia limited in much of the upper troposphere. While the conventional expectation holds that ammonia is efficiently scavenged by cloud and rain droplets during convection, strongly enhanced levels of ammonia and ammonium nitrate are observed in the Asian monsoon upper troposphere. By co-condensing with abundant nitric acid, ammonia can drive the growth of newly-formed ammonium sulfate/nitrate particles to well above CCN size. Our simultaneous ice nucleation ability measurements confirm that these particles are almost all efficient ice nucleus (IN). Further, we present complementary global model and cloud trajectories simulations that corroborate these implications. We show that ammonia can be transported by the convective systems, and subsequently drive intense HNO3–H2SO4–NH3 nucleation in the Asian monsoon upper troposphere, producing particles that can travel across the mid-latitude Northern Hemisphere.