The application of mass spectrometric techniques to the on-line measurement and characterization of aerosols has brought significant advances in the field of atmospheric science. This review focuses on the aerosol mass spectrometer (AMS), an instrument designed and developed at Aerodyne Research, which has been used most widely for the quantitative measurement of atmospheric fine particles. This manuscript presents a brief discussion on the strengths and limitations of the AMS measurement approach and reviews how the measurement data are utilized to characterize particle properties. The results from several laboratory experiments and field measurements are also introduced to highlight the different applications of this instrument.
Single particle mass spectrometric (SPMS) technique enables us to investigate chemical composition of individual particles with diameter from 100 nm to several µm in real-time without any cumbersome chemical treatment and analysis. SPMS also can detect a wide range of chemical compounds such as inorganic, organic, metal composition, and biological matter, including refractory materials, such as elemental carbon, sea salt, and dust, which are difficult to be analyzed with other on-line chemical particle analyzers. Since its introduction to aerosol research, SPMS technique has developed new fields in aerosol chemistry and physics by providing information on chemical composition and mixing state and their variability in time, space, and geographical location. In this review, starting with an overview on the SPMS instruments and history of the SPMS technique, aerosol researches which utilized unique capability of SPMS are briefly reviewed.
Understanding the formation processes of secondary aerosols in the atmosphere requires quantitative information on their precursor gaseous species. This article describes the application of the chemical ionization mass spectrometry (CIMS) including proton transfer reaction mass spectrometry (PTR-MS) to real-time and highly selective measurement of gaseous species involved in the secondary aerosol formation. The principles and characteristics of CIMS are presented, followed by the representative studies using CIMS in measuring both inorganic and organic gaseous species which may play an important role in the secondary aerosol formation. Finally, future prospects including the application of CIMS and PTR-MS to analysis of the aerosol chemical composition are presented.
Ambient corona discharge has been used as an ionizer in a wide range of research and industrial fields such as environmental, analytical and aerosol sciences, and possibly even commercial electric appliances. Terminal ions produced via ion evolutions through successive ion-molecule reactions in corona discharge can readily and efficiently supply the charge for ionization in ambient air. Despite substantial progress in the application of corona discharge, the elementary processes involved in terminal ion formation and evolution are not yet well understood. It has been reported that negative ion evolution is rather complex compared to that of positive ions, and that it is difficult to regulate the reproducible formation of specific negative ion species. We have recently established an atmospheric pressure corona discharge system containing a specific corona needle that successfully leads to regular and reproducible generation of various positive and negative ions originating from ambient air. The system coupled with mass spectrometers made it possible to study the relationship between terminal ion formation and discharge conditions. In this paper, the formation and evolution mechanism of terminal ions such as H3O+, HO-, NOx- and COx- depending on the electric field strength on the needle tip and the resulting kinetic energy of electrons accelerated at the tip will be described.
The air/water interface plays ubiquitous and fundamental roles in atmospheric chemistry and biochemistry involving reactive gas uptake on aerosol/seawater surface and natural defense mechanism by epithelial lining fluids that protects our lungs from the attack of air pollution. Previous studies partly revealed unexpected features of gas-liquid interactions including enhanced reactivity, presence of surface complexes or enhanced anion concentration. Molecular dynamics simulations and surface-sensitive spectroscopic studies show a progress for molecular-level understanding of gas-liquid interface. Here, we review a recent development of novel application of electrospray ionization that could directly monitor chemical reactions at the air/water interface, in which the aerial interface of liquid microjet sprayed into reactive gas is monitored via electrospray mass spectrometry. Because the ions are ultimately ejected from the topmost layers of initial liquid microjet, the change of chemical compositions at the air/water interface can be selectively measured. This novel technique is demonstrated to be a powerful tool in investigating rapid interfacial reactions that could be used for various scientific fields.
We performed long-term continuous, measurements of water-soluble ionic species and total trace metals in aerosols in Sapporo from April 1991 to December 2006. The annual mean concentrations of Na+ and Cl- increased in Sapporo from 1991 to 2000. These species are the indicators of sea-salt particles. The monthly mean showed high concentrations in March and October, while July showed lower values. The chlorine loss and/or contribution of Na+ from mineral dust were observed frequently from winter to spring. Increase rates of anthropogenic emissions of acidifying pollutants were observed for nss-SO42- (62.2%) and NO3- (81.5%) over a ten year period. SO2 and NOX emissions in East Asia have rapidly increased since the 1980s. But these emissions in Sapporo have not increased from 1991 to 2006. Therefore, nss-SO42- and NO3- increase in Sapporo is due to the transport of anthropogenic acidifying pollutants from the continent. These species showed high concentrations in spring to summer due to anthropogenic acidifying pollutants over inland Hokkaido. The variations of nss-Ca2+, Al, Fe, Ti, Mn, Ca, and Mg showed high concentrations during spring. The annual mean concentrations of Ti, Mn, Ca, and Mg decreased from 1997 to 2006. Therefore, the transportation of mineral dust to Sapporo decreased slightly during the ten years of observation. Concentration ratios of Pb/Zn and Ca/Al showed characteristic values in winter when the air mass had traveled over Central China and the Korean Peninsula.
Water-insoluble filtered residue materials of atmospheric wet and dry deposition are composed of mineral dusts and organic materials such as pollens. The number of pollens in the filter residue of deposition samples at Tottori was counted for 2 sizes at about 45 and 30 µm using a confocal laser microscope. Non-destructive X-ray fluorescence (XRF) analysis was used to measure Fe content of the filter residue. Relationship between Fe content analyzed by XRF and insoluble residue weight corrected for pollen weight assuming pollen density of 0.9 g/cm3 showed a linear relationship, suggesting that insoluble residue corrected for pollen weight contains Fe of 3.7 % by weight on the average. The average Fe content is consistent with the values reported for Asian dust (Kosa) events in Korea and China. Because Fe content of insoluble residue in filter samples is easily measured by XRF method, mineral dust amounts in the filter residue samples can be estimated from Fe content of the sample and the average fraction of Fe for Asian dust.
We conducted precise measurements of electrical mobilities of negatively charged metal nanoparticles in Ar gas using a differential mobility analyzer. The measured inverse mobilities were larger than those calculated from the hard-sphere collision model. We propose a formula describing the relationship between the electrical mobilities and the diameters of particles measured using transmission electron microscopy, which corrects the deviation from the hard-sphere collision model.