The atmospheric behavior of nitrous acid, HONO, was discussed on the basis of field measurements by an annular-denuder or a filter-pack method at four different nature sites in northern Japan, Sapporo (urban), Moshiri (rural), Rishiri (coastal remote) and Teshio (mountainous remote), in terms of their atmospheric chemistry parameters including nitrogen oxides, nitric acid, nitrate aerosol and ozone. The annual mean concentrations of HONO in Sapporo ranged from 36 to 41 nmol m^-3 where the concentration level was 11 to 31 times higher than those for the other sites. A different seasonality of the HONO concentration was detected at the different nature site: the urban site showed a maximum in the winter, the remote in the summer, and the rural in the winter and the summer. A heterogeneous reaction between NO₂ and H₂O on the surface of airborne particles and the ground surface is likely to play a significant role in the nitrous acid formation because the HONO/NOx ratio in ambient air is higher than those by direct emission as reported by Kurtenbach et al. (2001). In the case of the ground-surface heterogeneous reaction, the concentration gradient of HONO is expected to negative correlate with that of NO₂ because the deposition of NO₂ would induce emissions of HONO into the atmosphere. Actually, in Teshio, the difference between the concentrations of HONO at the heights of 30 m and 10 m positive correlated with that for NO₂. Furthermore, the Rishiri measurements showed a significant correlation between the concentrations of HONO and PM₁₀. In addition, Rishiri and Moshiri measurements showed significant correlations between the concentration ratio, HONO/NO₂, and absolute humidity. These results strongly support the view that the heterogeneous reactions on the airborne particles prevails in the formation of HONO in the rural and remote areas with considerably low concentrations of NO₂. On the other hand, the heterogeneous reaction on the ground-surface reaction plays a significant role in Sapporo, especially in the winter with high NO₂ concentrations. In Sapporo, negative correlations were detected in the winter between the concentrations of HONO and NO, and between of HNO₃ and O₃, which would be attributable to the insufficient conversion of NO₂ to HNO₃, and further to nitrate species, under urban conditions because of the low concentration of ozone along with high concentrations of NO. These field measurements would indicate that the behavior of nitrous acid is controlled by the chemical reactions of NO₂ with H₂O, and that this heterogeneous reaction was affected by the NO₂ concentration, absolute humidity and O₃ concentration.

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A two-year monitoring of the vertical distribution of ammonia (NH₃) was conducted in the atmosphere above an intensive dairy farming area in central Japan. Passive samplers monitored the fortnightly-mean concentrations of NH₃ at six heights up to 40.0 m from the ground surface. The highest biennial-mean concentration was observed at a height of 5.7 m (26.5 μg NH₃ m^-3, 0 °C and 1013 hPa), while the lowest value was observed at a height of 40.0 m (15.4 μg NH₃ m^-3). The fortnightly-mean concentrations of NH₃ at a height of 40.0 m showed a clear seasonal pattern; i.e., high in the warm season from April to September (19.1-19.7 μg NH₃ m^-3) and low in the cold season from October to March (11.4-11.7 μg NH₃ m^-3). Comparatively speaking, the seasonal patterns of the fortnightly-mean concentrations of NH₃ were inconsistent at the lower heights, perhaps due to the direct effects of NH₃ emitted from field-applied manure and/or slurry at the neighboring forage crop fields. Excluding the lowest interval of heights (1.0-5.7 m), in many cases, the gradients of the NH₃ concentrations showed an emission tendency which suggested that the study area acted as a year-round emitter of NH₃ into the atmosphere.

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A High-Volume Impactor for PM_2.5 (HVI_2.5) was developed which can be attached to conventional High-Volume air samplers with 20.3×25.4 cm aerosol filter. Its simple structure results in a light weight (<1 kg) and compact size, therefore, it can be easily handled and operated in field measurements. Another advantage of the HVI_2.5 is that the operator can observe the aerosol-loaded filter through a transparent side wall. In a preliminary test to determine its size separation characteristics using ambient aerosols, the HVI_2.5 successfully yielded a 50% cut-off aerodynamic diameter of 2.5 μm at the flow rate of 740 L min^-1.

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The U.S. EPA has determined that the existing primary annual standard (53 ppb) for nitrogen dioxide (NO₂) is not sufficient to protect public health with an adequate margin of safety, therefore, the Administrator has established a new short-term primary standard (1-hour standard of 100 ppb) that will afford increased protection for asthmatics and other at-risk populations against an array of adverse respiratory health effects related to short-term NO₂ exposure on January 22, 2010. This paper reviews the revision process of the NO₂ standard by the EPA with a brief review of the NO₂ standard in Japan.

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