We have been monitoring the air pollutants at the Tokyo Skytree (TST) in order to understand the air quality over central Tokyo. Focusing on the haze event on the 9th and 10th December 2015, we analyzed the causes of the event and differences in the air quality between the ground and upper levels. In the afternoon on Dec. 9, as a result, higher concentrations of SO₂ were observed at 320 m AGL on Tokyo Skytree (H320) than near the ground surface (H10). It is likely that a boundary layer was formed from 18:00, and H320 had been influenced by large-point sources and ships. In the night of Dec. 10 when the PM_2.5 concentrations went over 90 μg/m³ around central Tokyo, an inversion layer was formed associated with a local front (the so-called the Boso front line). This polluted air mass seemed to be centered at the southeastern part of the 23 wards of Tokyo and distributed below 200 m AGL from 22:00 to 23:00. We also found that the number concentration ratios (N_H320/N_H10) of smaller particles measured at H320 to H10 increased earlier than those of the larger particles.

The tropospheric ozone concentration is expected to increase with elevation of the air temperature under global warming. To estimate the ozone threat to appearance quality of Japanese rice grains under global warming conditions, we conducted ozone exposure combined with a temperature rise of 1.7℃ in open-top chambers using 17 Japanese cultivars. The fraction of chalky grains in most cultivars grown in northern Japan significantly increased by the elevated ozone and combination of elevated ozone and air temperature. Significant positive correlations were found between the ozone dose during grain ripening period and fraction of chalky grains in ‘Satonoyuki’ and ‘Koshihikari’ with and without air temperature elevation. The combined effects of air temperature and ozone elevation were additive in ‘Koshihikari’, but were greater than additive in ‘Satonoyuki’. A two-way analysis of variance showed that the ozone-temperature interaction in the formation of chalky grains was not identified in some rice cultivars investigated here, suggesting that there is varietal difference in the mechanism of chalky grain formation by ozone under the elevated air temperature condition. Moreover, there is significant negative correlation between amylose content in brown rice and the rate of chalky grain under elevated ozone. This suggests that the appearance quality of grains in rice cultivars with lower amylose content tend to be deteriorated by elevated ozone, and the deterioration of grain quality with ozone is enhanced even further by the temperature elevation.

The ion concentration in the rainwater at a coastal site in southwestern Japan during the period 1996–2003 was investigated according to the rain types of cyclones (Cy), stationary fronts (SF) and typhoons (Ty). The eight-year mean concentrations of Na⁺, Cl⁻, nss-SO₄²⁻, NO₃⁻, NH₄⁺ and nss-Ca²⁺ in the Cy rainwater were 68.6±33.1, 80.9±40.9, 32.1±8.8, 14.4±3.7, 15.3±3.5 and 8.3±3.4 μeq/L, respectively. In contrast, the respective concentrations of these ions in the SF rainwater were 24.9±6.2, 30.2±6.9, 18.2±7.5, 8.1±3.1, 9.9±4.2 and 4.4±2.7 μeq/L. In the Ty rainwater (11 cases in total), the concentrations of Na⁺ and Cl⁻ were 227.7±518.3 μeq/L and 275.6±619.4 μeq/L, respectively, together constituting 79.2% of the ion content. Backward trajectories and statistical analyses revealed that differences in ion concentration between the Cy and SF rainwater were due to the different air parcels origins and chemical processes. The yearly mean ion concentrations in the total rainwater were dominated by the Cy and SF rain. A simple estimation according to the rainfall variation by SF showed that the variation could cause a significant change in the ion concentrations. Considering the distinctiveness of the rain types is thus essential for an accurate evaluation of ions in the rainwater, a meaningful inter-comparison between regions, and a more confident projection of future scenarios of rainwater chemistry.

It has been pointed out that a chemiluminescence method, the official method for measuring nitrogen oxides, overestimates concentrations of nitrogen oxides. We performed continuous intercomparison measurements of nitrogen oxides between the official and accurate methods developed in the previous study in the urban area. In this article, concentrations of nitrogen oxides measured by the accurate and official methods are defined as NO_x and NO_x^*, respectively. The official method overestimated concentrations of nitrogen oxides regardless of the time of the day and seasons. The annual means of NO_x^*–NO_x and NO_x^*/NO_x for 1-h averaged values were 3.38 ppbv and 1.32, respectively. Good correlations between NO_x^*–NO_x and oxidant (Ox=O₃+NO₂–0.1NO_x) concentrations were obtained, especially in the summer daytime. This result indicates that the concentrations of nitrogen oxides were more overestimated by the official method when photochemical reactions in the atmosphere were more active. On the other hand, high NO_x^*–NO_x was observed in the nighttime, i.e., under the low photochemical activity, suggesting the contribution of odd nitrogen species produced in the dark condition such as nitrous acid and dinitrogen pentoxide.