Huajun Mai
A5008612776- Atmospheric chemistry and aerosols
- Atmospheric aerosols and clouds
- Atmospheric Ozone and Climate
- Air Quality and Health Impacts
- Coagulation and Flocculation Studies
- Air Quality Monitoring and Forecasting
- Iron oxide chemistry and applications
- Electrostatics and Colloid Interactions
- Nuclear Physics and Applications
- Water Quality Monitoring and Analysis
- Radiation Effects and Dosimetry
- Ion-surface interactions and analysis
- Electrochemical Analysis and Applications
- Bacterial Identification and Susceptibility Testing
- Cyclone Separators and Fluid Dynamics
- Spectroscopy Techniques in Biomedical and Chemical Research
- Phase Equilibria and Thermodynamics
- Advanced Chemical Physics Studies
- Mass Spectrometry Techniques and Applications
- Dark Matter and Cosmic Phenomena
- Gold and Silver Nanoparticles Synthesis and Applications
- Luminescence Properties of Advanced Materials
- Catalytic Processes in Materials Science
- Aerosol Filtration and Electrostatic Precipitation
- Integrated Circuits and Semiconductor Failure Analysis
California Institute of Technology
2017-2025
State Key Joint Laboratory of Environment Simulation and Pollution Control
2013
Tsinghua University
2013
Vietnam Atomic Energy Instiute
1996-1998
Atmospheric aerosol formation from biogenic vapors is strongly affected by air pollutants, like NO x , SO 2 and NH 3 .
Significance Aerosol particles can form and grow by gas-to-particle conversion eventually act as seeds for cloud droplets, influencing global climate. Volatile organic compounds emitted from plants are oxidized in the atmosphere, resulting products drive particle growth. We measure growth biogenic vapors with a well-controlled laboratory setup over wide range of tropospheric temperatures. While higher temperatures lead to increased reaction rates concentrations highly molecules, lower allow...
Abstract. Highly oxygenated organic molecules (HOMs) contribute substantially to the formation and growth of atmospheric aerosol particles, which affect air quality, human health Earth's climate. HOMs are formed by rapid, gas-phase autoxidation volatile compounds (VOCs) such as α-pinene, most abundant monoterpene in atmosphere. Due their abundance low volatility, can play an important role new-particle (NPF) early aerosols, even without any further assistance other low-volatility sulfuric...
NO x is important for particle growth as it can participate in HOM formation and alter the volatility distribution.
Abstract. Nucleation of atmospheric vapours produces more than half global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly oxygenated products can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together isoprene (C5H8), which the highest emission all organic vapours. Previous have shown suppresses new-particle formation from monoterpenes, but cause this...
Abstract. Recent advances in our knowledge of the gas-phase oxidation isoprene, impact chamber walls on secondary organic aerosol (SOA) mass yields, and measurement analysis techniques warrant reevaluating SOA yields from isoprene. In particular, isoprene under high-NOx conditions forms via two major pathways: (1) low-volatility nitrates dinitrates (LV pathway) (2) hydroxymethyl-methyl-α-lactone (HMML) reaction a surface or condensed phase particles to form 2-methyl glyceric acid its...
Abstract. New particle formation (NPF) is a significant source of atmospheric particles, affecting climate and air quality. Understanding the mechanisms involved in urban aerosols important to develop effective mitigation strategies. However, NPF rates reported polluted boundary layer span more than 4 orders magnitude, reasons behind this variability are subject intense scientific debate. Multiple vapours have been postulated participate NPF, including sulfuric acid, ammonia, amines...
The prevailing treatment of secondary organic aerosol formation in atmospheric models is based on the assumption instantaneous gas-particle equilibrium for condensing species, yet compelling experimental evidence indicates that aerosols can exhibit properties highly viscous, semisolid particles, which may be achieved slowly. approach to partitioning controlled by gas-phase diffusion, interfacial transport, and particle-phase diffusion. Here we evaluate controlling processes time scale...
Abstract. The formation of secondary particles in the atmosphere accounts for more than half global cloud condensation nuclei. Experiments at CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined importance ions new particle formation, but quantifying their effect remains challenging. By using a novel instrument setup consisting two nanoparticle counters, one them equipped with an ion filter, we were able to further investigate ion-related mechanisms formation. In autumn...
Abstract Exposure to anthropogenic atmospheric aerosol is a major health issue, causing several million deaths per year worldwide. The oxidation of aromatic hydrocarbons from traffic and wood combustion an important source low-volatility species in secondary organic aerosol, especially heavily polluted environments. It not yet established whether the formation involves mainly rapid autoxidation, slower sequential steps or combination two. Here we reproduced typical urban haze ‘Cosmics...
Analysis of scanning electrical mobility spectrometer (SEMS) or SMPS data requires coupling the differential analyzer (DMA) transfer function with response functions for instrument plumbing and detector. In limit plug flow (uniform velocity) within DMA, DMA has same form as that constant voltage. Most SEMS/SMPS analysis uses this model, though previous studies have shown boundary layers distort during measurements. Part I determined instantaneous TSI Model 3081 A long column by modeling...
The scanning electrical mobility spectrometer (SEMS; also known as the particle sizer, SMPS) enables rapid size distribution measurements with a differential analyzer (DMA)/condensation counter (CPC) combination by ramping classifier voltage, and continuously counting particles into time bins throughout scan. Inversion of poses challenge due to finite response CPC; distorted data can be deconvoluted improve fidelity distributions obtained SEMS/SMPS. Idealized models classification region...
We present the design, simulation, and characterization of radial opposed migration ion aerosol classifier (ROMIAC), a compact differential electrical mobility classifier. evaluate performance ROMIAC using combination finite element modeling experimental validation two nearly identical instruments tetra-alkyl ammonium halide mass standards sodium chloride particles. Mobility efficiency calibrations were performed over wide range particle diameters flow rates to characterize under anticipated...
Abstract. New-particle formation (NPF) is a significant source of atmospheric particles, affecting climate and air quality. Understanding the mechanisms involved in urban aerosols important to develop effective mitigation strategies. However, NPF rates reported polluted boundary layer span more than four orders magnitude reasons behind this variability subject intense scientific debate. Multiple vapours have been postulated participate NPF, including sulfuric acid, ammonia, amines organics,...
Abstract. Particle size measurement in the low nanometer regime is of great importance to study cloud condensation nuclei formation and better understand aerosol-cloud interaction. Here we present design, modeling, experimental characterization nano-scanning electrical mobility spectrometer (nSEMS), a recently developed instrument that probes particle physical properties 1.5–25 nm range. The nSEMS consists charge conditioner, novel differential analyzer, two-stage counter (CPC). conditioner...
Abstract. Nucleation of atmospheric vapors produces more than half global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly-oxygenated products can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together isoprene (C5H8), which the highest emission all organic vapors. Previous have shown suppresses new-particle formation from monoterpenes, but cause this...
Abstract. Particle size measurement in the low nanometer regime is of great importance to study cloud condensation nuclei formation and better understand aerosol–cloud interactions. Here we present design, modeling, experimental characterization nano-scanning electrical mobility spectrometer (nSEMS), a recently developed instrument that probes particle physical properties 1.5–25 nm range. The nSEMS consists novel differential analyzer two-stage counter (CPC). analyzer, radial...
Abstract. The formation of secondary particles in the atmosphere accounts for more than half global cloud condensation nuclei. Experiments at CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber have underlined importance ions new particle formation, but quantifying their effect remains challenging. By using a novel instrument setup consisting two nano-particle counters, one them equipped with an ion filter, we were able to further investigate ion-related mechanisms formation. In autumn...
Abstract. Highly-oxygenated organic molecules (HOMs) contribute substantially to the formation and growth of atmospheric aerosol particles, which affect air quality, human health Earth's climate. HOMs are formed by rapid, gas-phase autoxidation volatile compounds (VOCs) such as α-pinene, most abundant monoterpene in atmosphere. Due their abundance low volatility, can play an important role for new-particle (NPF) early aerosols, even without any further assistance other low-volatility...
Abstract. Recent advances in our knowledge of the gas-phase oxidation isoprene, impact chamber walls on secondary organic aerosol (SOA) mass yields, and measurement analysis techniques warrant re-evaluating SOA yields from isoprene. In particular, isoprene under high-NO conditions forms via two major pathways: (1) low-volatility nitrates dinitrates (LV pathway) (2) hydroxymethyl-methyl-α-lactone (HMML) reaction a surface or condensed phase particles to form 2-methyl glyceric acid its...