Search NASA⌕ Search

Engineering topics

Liu, Yongchun

Publications and source records attributed to Liu, Yongchun.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

The Significant Role of New Particle Composition and Morphology on the HNO 3 -Driven Growth of Particles down to Sub-10 nm

New particle formation and growth greatly influence air quality and the global climate. Recent CERN Cosmics Leaving OUtdoor Droplets (CLOUD) chamber experiments proposed that in cold urban atmospheres with highly supersaturated HNO 3 and NH 3 , newly formed sub-10 nm nanoparticles can grow rapidly (up to 1000 nm h –1 ). Here, we present direct observational evidence that in winter Beijing with persistent highly supersaturated HNO 3 and NH 3 , nitrate contributed less than ~14% of the 8–40 nm nanoparticle composition, and overall growth rates were only ~0.8–5 nm h –1 . To explain the observed growth rates and particulate nitrate fraction, the effective mass accommodation coefficient of HNO 3 (α HNO 3 ) on the nanoparticles in urban Beijing needs to be 2–4 orders of magnitude lower than those in the CLOUD chamber. We propose that the inefficient uptake of HNO 3 on nanoparticles is mainly due to the much higher particulate organic fraction and lower relative humidity in urban Beijing. To quantitatively reproduce the observed growth, we show that an inhomogeneous “inorganic core–organic shell” nanoparticle morphology might exist for nanoparticles in Beijing. Finally, this study emphasized that growth for nanoparticles down to sub-10 nm was largely influenced by their composition, which was previously ignored and should be considered in future studies on nanoparticle growth.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Regime-Dependence of Nocturnal Nitrate Formation via N 2 O 5 Hydrolysis and Its Implication for Mitigating Nitrate Pollution

The heterogeneous hydrolysis of dinitrogen pentoxide (N 2 O 5 ) is an important pathway in nitrate formation; however, its formation rate and relative contribution to total particulate nitrate (pNO 3 - ) are highly variable. Here we report that nocturnal pNO 3 - formation via N 2 O 5 hydrolysis is dependent on the regime defined by the ratio of NO 2 to O 3 . Nocturnal pNO 3 - formation via N 2 O 5 hydrolysis is suppressed in an O 3 -limited regime but enhanced in a NO 2 -limited regime. The results have crucial implications for effective control of nitrate pollution in the future. An exclusive decrease in NO 2 will decrease nocturnal pNO 3 - formation in a NO 2 -limited regime but may be less effective or even increase nocturnal pNO 3 - formation in an O 3 -limited regime.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

The missing base molecules in atmospheric acid–base nucleation

Abstract Transformation of low-volatility gaseous precursors to new particles affects aerosol number concentration, cloud formation and hence the climate. The clustering of acid and base molecules is a major mechanism driving fast nucleation and initial growth of new particles in the atmosphere. However, the acid–base cluster composition, measured using state-of-the-art mass spectrometers, cannot explain the measured high formation rate of new particles. Here we present strong evidence for the existence of base molecules such as amines in the smallest atmospheric sulfuric acid clusters prior to their detection by mass spectrometers. We demonstrate that forming (H2SO4)1(amine)1 is the rate-limiting step in atmospheric H2SO4-amine nucleation and the uptake of (H2SO4)1(amine)1 is a major pathway for the initial growth of H2SO4 clusters. The proposed mechanism is very consistent with measured new particle formation in urban Beijing, in which dimethylamine is the key base for H2SO4 nucleation while other bases such as ammonia may contribute to the growth of larger clusters. Our findings further underline the fact that strong amines, even at low concentrations and when undetected in the smallest clusters, can be crucial to particle formation in the planetary boundary layer.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Responses of gaseous sulfuric acid and particulate sulfate to reduced SO 2 concentration: A perspective from long-term measurements in Beijing

SO 2 concentration decreased rapidly in recent years in China due to the implementation of strict control policies by the government. Particulate sulfate ( p S O 4 2 - ) and gaseous H 2 SO 4 (SA) are two major products of SO 2 and they play important roles in the haze formation and new particle formation (NPF), respectively. We examined the change in p S O 4 2 - and SA concentrations in response to reduced SO 2 concentration using long-term measurement data in Beijing. Simulations from the Community Multiscale Air Quality model with a 2-D Volatility Basis Set (CMAQ/2D-VBS) were used for comparison. From 2013 to 2018, SO 2 concentration in Beijing decreased by ~81% (from 9.1 ppb to 1.7 ppb). p S O 4 2 - concentration in submicrometer particles decreased by ~60% from 2012–2013 (monthly average of ~10 μg·m - 3 ) to 2018–2019 (monthly average of ~4 μg·m - 3 ). Accordingly, the fraction of p S O 4 2 - in these particles decreased from 20–30% to <10%. Increased sulfur oxidation ratio was observed both in the measurements and the CMAQ/2D-VBS simulations. Despite the reduction in SO 2 concentration, there was no obvious decrease in SA concentration based on data from several measuring periods from 2008 to 2019. This was supported by the increased SA:SO 2 ratio with reduced SO 2 concentration and condensation sink. NPF frequency in Beijing between 2004 and 2019 remains relatively constant. Finally, this constant NPF frequency is consistent with the relatively stable SA concentration in Beijing, while different from some other cities where NPF frequency was reported to decrease with decreased SO 2 concentrations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗