This study reports the frequency of open burning, which was observed in two ways in Tsukuba-city, Ibaraki prefecture. First, the daily frequency between September and October, 2015, showed that the quantity increased before rainfall and that the rice residues, 57% of the total open burning, were burned in the order of hulls, then straw after harvesting. Secondary, the monthly frequency showed that the quantity tended to decrease from September, 2015, to August, 2016. The monthly frequency, which was taken by fixed point cameras on the top of Mt. Tsukuba, showed that the quantity tended to decrease from October, 2015, to May, 2016, and also showed that the quantity tended to increase on 10–11 am and 2–3 pm within a day. Based on these observations, a method to distribute the temporal emission ratio caused by rice straw open burning, which is expected to improve the accuracy of regional emissions and forecasting, has been developed. The regression coefficients indicated that the quantity of open burning increases before rain and decreases due to strong wind. Applying the model to the prefectural rice harvest terms and weather data, the prefectural daily PM (particulate matter) emission ratios are estimated.
15 organic tracer compounds were analyzed at 3-hr intervals of PM2.5 samples collected by a PTFE tape filter during a high concentration event on December 9 and 10, 2015, in Nagoya. Compounds indicating primary emission burning from biomass, such as levoglucosan, and plastics, such as terephthalic acid, showed a similar temporal variation in the PM2.5 concentration which had peaks during the nights of 9 and 10 December. However, some organic tracer compounds originating from a secondary formation in the atmosphere, such as malic acid, showed a peak only on December 10. The primary emission sources contributed to the high concentration event of PM2.5, because the averaged weight fractions of the primary emission tracers relative to the PM2.5 concentration showed a similar variation to the PM2.5. However, those of the secondary formation tracers did not increase during the evening of 9 December, and only those of both succinic acid and 3-hydroxyglutaric acid showed a peak at midnight on 10 December. These results indicated different contributions of the primary emission and secondary formation to the high concentration event of PM2.5 during the observation period of this study. A higher time-resolution analysis of organic tracer compounds is a powerful tool to reveal factors causing high concentration events with a large temporal variation.
To estimate the dry deposition of atmospheric mercury, it is important to determine the size distribution of particle-bound mercury (particulate mercury, PHg) because the dry deposition velocity mostly depends on the particle size. Size-segregated particle matters (PM) were collected using two types of impactor samplers, namely, the PM2.5 sampler and Andersen cascade impactor sampler, on the roof of the Niigata Institute of Technology located in the rural area of Kashiwazaki City, Niigata Prefecture. The mercury contents in the PM were measured by flameless cold atomic absorption spectrophotometry using a combustion gold-trapping heat vaporization method. The ratios of the coarse PHg to total PHg indicated significant positive correlations at ambient temperatures during the sampling periods in both methods, i.e., higher percentages of coarse PHg were observed during the warm season and the percentages of the fine PHg increased in the cold season. When estimating the dry depositions of atmospheric mercury in a coastal area via such an inferential method, it is necessary to consider the ambient temperature dependence of the PHg size distribution.
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