For particulate carbon analysis, by the widely used thermal method, the pyrolysis of organic carbon (OC) causes an overestimate of elemental carbon (EC). However, recently the thermal/optical method, that is capable of pyrolysis correction by monitoring the reflected and/or transmitted lights of a sample filter during analysis, is becoming popular. In this study, the thermal and the thermal/optical methods were compared using the same ambient samples collected at an urban and a rural site in winter and summer. For both methods, OC and EC were separated at 550° in 100% a helium atmosphere. There was less difference for the total carbon (TC) concentration, whereas EC and OC concentrations were varied with the methods. For EC, the concentration by the thermal/optical method was smaller than the thermal method (the slope of regression line was 0.70 for the thermal vs. the thermal reflectance method; 0.34 for the thermal vs. the thei: nal transmittance method). Moreover, the influence of seasons, sampling sites, and particle size on EC and OC concentrations were also examined; however, these factors did not contribute as much as the analysis methods. Additionally, using samples with a 100% cutoff diameter of 10μm collected by a low volume sampler (LVS) and a high-volume sampler (HVS) simultaneously, the total mass and carbonaceous particle concentrations measured from LVS and HVS samples were compared. The total mass, EC, and OC concentrations by HVS were about 15%, 20%, and 40% smaller than LVS, respectively.

View full abstract

In Japan, the nation-wide annual-mean concentration of suspended particulate matter (SPM) dramatically decreased, and the achievement rate of the air quality standard of SPM was considerably improved in FY1999. This study shows the actual conditions and meteorological causes of the low concentration. The nation-wide monthlymean concentration of SPM was low in April, from June to August, and in February in FY 1999. In July and August, the SPM concentration was remarkably low in Kanto, where the SPM concentration was characterized with very low concentrations continuing for as long as a week or more. Meteorological factors were analyzed for the low concentrations in Kanto in July and August, 1999. On a monthly basis, these two months of 1999 were characterized by stronger wind speeds and more precipitation than the five years around 1999, which could be causes of the low concentration. In the very low concentration weeks, however, such low concentrations were related to the mostly constant wind direction, which brought maritime air from the Pacific Ocean.

View full abstract

Ozone concentrations in some areas tend to be higher on weekends than on weekdays, in spite of the fact that ozone precursors are lower on weekends than on weekdays. This phenomenon is known as the “Weekend effect.” As a result of the analysis of data gathered from monitoring stations over the period 1976-2003, the weekend effect was observed at all 13 of the selected monitoring stations in Hyogo prefecture. The weekend-weekday difference of the concentration of photochemical oxidants (O_x), which was averaged over the measurement period at all stations, was 6%; while those of nitric oxide (NO), oxides of nitrogen (NO_x) and non-methane hydrocarbons (NMHC) were-34%, -27% and -16%, respectively. The weekend effect varied in areas, with the maximum difference of O_x at Amagasaki City, 11%, and the minimum difference at Tamba City, 1%. The diurnal variation in O_X by day of week at Amagasaki City in 1997, when the annual weekend-weekday difference of O_x was the greatest, showed that the concentrations of O_x were higher on Saturday afternoon and Sunday all day compared to weekdays. The following causes for the weekend effect were considered, (1) less ozone quenching by NO emission reductions, (2) NO_x emission reductions under VOC-limited conditions.

View full abstract

Proton transfer reaction mass spectrometry (PTR-MS) is a technique that has been developed recently. It has several advantages for the measurement of volatile organic compounds (VOCs) in the atmosphere. The PTR-MS instrument can detect OVOCs with high time resolution, as well as VOCs without the pre-condensation procedure. Although the PTR-MS is available as a commercial instrument from the IONICON company, the instrument requires calibrations for the determination of absolute concentration. In this study, calibrations of the PTR-MS instrument were carried out for OVOCs with diffusion tubes and several kinds of premixed standard gas cylinders. Substances used for calibration with the diffusion tube were as follows; acetonitrile (CH₃CN), methanol (CH₃OH), acetone (CH₃COCH₃), and acetaldehyde (CH₃CHO). The results of these substances showed good linearity. The time variations of the calibration factors were almost constant for two months.
The calibration factor of formaldehyde (HCHO) was found to depend on water vapor. This phenomenon is explained by the reverse reaction between HCHOH⁺ and H₂O. Signals of HCHO in wet conditions decreased 60% less than those in dry conditions. The back reaction rate constant (k₂) was estimated at 3×10^-11 [cm³ molecule^-1 s^-1] using the box model calculation.
Measurements in the ambient air in Tokyo were carried out. About 30 species containing OVOCs, aromatics and biogenic volatile organic compounds were measured. These showed characteristic diurnal variations. Aldehydes, acetone and isoprene concentrations had a daytime peak. On the contrary, aromatics had peaks in the evening. Methanol was almost constant. Thus, OVOCs concentrations can be measured by PTR-MS.

View full abstract