Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

The application of mass spectrometric techniques to the real-time measurement and characterization of aerosols represents a significant advance in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, Inc. (ARI) that is the most widely used thermal vaporization AMS. The AMS uses aerodynamic lens inlet technology together with thermal vaporization and electron-impact mass spectrometry to measure the real-time non-refractory (NR) chemical speciation and mass loading as a function of particle size of fine aerosol particles with aerodynamic diameters between approximately 50 and 1,000 nm. The original AMS utilizes a quadrupole mass spectrometer (Q) with electron impact (EI) ionization and produces ensemble average data of particle properties. Later versions employ time-of-flight (ToF) mass spectrometers and can produce full mass spectral data for single particles. This manuscript presents a detailed discussion of the strengths and limitations of the AMS measurement approach and reviews how the measurements are used to characterize particle properties. Results from selected laboratory experiments and field measurement campaigns are also presented to highlight the different applications of this instrument. Recent instrumental developments, such as the incorporation of softer ionization techniques (vacuum ultraviolet (VUV) photo-ionization, Li+ ion, and electron attachment) and high-resolution ToF mass spectrometers, that yield more detailed information about the organic aerosol component are also described.

ABSTRACT. The importance of atmospheric aerosols in regulating the Earth's climate and their potential detrimental impact on air quality and human health has stimulated the need for instrumentation which can provide real-time analysis of size resolved aerosol, mass, and chemical composition. We describe here an ( ) aerosol mass spectrometer AMS which has been developed in response to these aerosol sampling needs and present results which demonstrate quantitative measurement capability for a laboratory-generated pure component NH NO aerosol. 3The instrument combines standard vacuum and mass spectrometric technologies with recently developed aerosol sampling techniques. A un ique aerodynamic aerosol ( ) inlet developed at the Un iversity of Minnesota focuses particles into a narrow beam and ef ciently transports them into vacuum where aerodynamic particle size ( ) is determined via a particle time-of-ight TOF measurement. Time-resolved particle mass detection is performed mass spectrometrically following particle ash vaporization on a resistively heated surface. Calibration data are presented for aerodynamic particle velocity and particle collection ef ciency measurements. The capability to measure aerosol size and mass distributions is compared ( ) to simultaneous measurements us ing a differential mobility analyzer DMA ( ) and condensation particle counter CPC . Quantitative size classi cation is demonstrated for pure component NH NO aerosols having mass concentrations 4 3 ) ; 0.25 m g m I 3 . Results of uid dynamics calculations illustrating the performance of the aerodynamic lens are also presented and compared to the measured performance. The utility of this AMS as both a laboratory and eld portable instrument is discussed.

and evolution of organic aerosol involves simultaneous changes to both carbon oxidation state 39 and carbon number (n C ).

Sulfate aerosols exert profound impacts on human and ecosystem health, weather, and climate, but their formation mechanism remains uncertain. Atmospheric models consistently underpredict sulfate levels under diverse environmental conditions. From atmospheric measurements in two Chinese megacities and complementary laboratory experiments, we show that the aqueous oxidation of SO 2 by NO 2 is key to efficient sulfate formation but is only feasible under two atmospheric conditions: on fine aerosols with high relative humidity and NH 3 neutralization or under cloud conditions. Under polluted environments, this SO 2 oxidation process leads to large sulfate production rates and promotes formation of nitrate and organic matter on aqueous particles, exacerbating severe haze development. Effective haze mitigation is achievable by intervening in the sulfate formation process with enforced NH 3 and NO 2 control measures. In addition to explaining the polluted episodes currently occurring in China and during the 1952 London Fog, this sulfate production mechanism is widespread, and our results suggest a way to tackle this growing problem in China and much of the developing world.sulfate aerosol | severe haze | pollution | human health | climate