Masahide Aikawa

Spatial Variations and Trends in Acid Deposition in Japan Within a 100 Km × 100 Km Region from 1989 to 1999

A monitoring network for acid deposition that consisted of five sites in Hyogo, Japan, and covered a region of about 100 km × 100 km revealed the spatial variations and trends in acid deposition in the region. Data from April 1989 to March 1999 were used for comparison and evaluation. Filtering-type bulk samplers were used. Only one rural site showed a significantly (p < 0.01) lower pH than the other four sites, although the pAi (−log([nss-SO2−4] + [NO−3])) at this site was not lower than those at the other sites. In contrast, the pH at two urban sites was not lower than those at the other three sites (suburban, rural, and remote), although the pAi at these sites was significantly lower than those at the other sites. The concentrations of NO−3, non-seasalt-(nss-)SO2−4, and nss-Ca2+ showed similar spatial variations. The concentrations of NO−3, nss-SO2−4, and nss-Ca2+ at the urban site were higher than those at the rural and remote sites, whereas the concentration of NH+4 showed a different spatial variation from NO−3, nss-SO2−4, and nss-Ca2+; i.e., the level at the remote site was similar to that at the urban site. The mean chemical compositions at the rural and remote sites were very similar. In addition, they had approximately equal concentrations. However, the only difference between the rural and remote sites was observed in the composition of NH+4 and H+; i.e., the concentration of NH+4 (or H+) at the rural site was lower (or higher) than that at the remote site. A large deposition of nss-Ca2+ was observed in the urban area and was attributed to effective neutralization in this area. The large deposition was synchronized with precipitation seasonally in the area where precipitation was high due to a large snowfall. The NO−3/nss-SO2−4 ratio (N/S ratio) showed a clear trend of increase, and the rate of increase during the investigation ranged from 34% to 59% from April 1989 to March 1999.

Difference between filtering-type bulk and wet-only data sets based on site classification

Abstract In order to clarify the limitations and the effectiveness of filtering-type bulk sampler, a study on precipitation collected by filtering-type bulk and wet-only samplers was performed. At an urban site, there was a statistically significant difference between the filtering-type bulk and wet-only samples at a 1% significance level in the pH and major chemical components. At a suburban site, pH, NH 4 + , and nss-Ca 2+ showed a difference at a 1% significance level and NO 3 − at a 5% significance level, but nss-SO 4 2− did not show any difference even at a 5% significance level. At a rural site, although there was a difference in nss-Ca 2+ at a 1% significance level and in pH at a 5% significance level, nss-SO 4 2− , NO 3 − , and NH 4 + did not show any difference. The attributions of the deposition of gaseous compounds and particulate matter in a filtering-type bulk sampler were estimated to be 32% (nss-SO 4 2− ), 46% (NO 3 − ), 36% (NH 4 + ), and 75% (nss-Ca 2+ ) at an urban site, 14% (nss-SO 4 2− ), 16% (NO 3 − ), 27% (NH 4 + ), and 42% (nss-Ca 2+ ) at a suburban site, and 16% (nss-SO 4 2− ), 17% (NO 3 − ), 19% (NH 4 + ), and 47% (nss-Ca 2+ ) at a rural site. The degree of pollution at a sampling site should be taken into account when using a data set collected with filtering-type bulk samplers.

Cloud Water Deposition to Forest Canopies of Cryptomeria Japonica at Mt.Rokko, Kobe, Japan

Cloud water deposition to canopies of Cryptomeria japonica at Mt.Rokko, Kobe, Japan, was estimated from throughfall measurements and fog water collections carried out during a full year. Annual cloud frequency was 11.5–15.5% and liquid water content (LWC) was 0.059 g/m3. Since cloud water deposition on to forest canopies was significantly correlated with the amount of fog water collected, the former parameter could be quantitatively derived from throughfall measurements. Annual cloud water deposition on to Cryptomeria canopies was 1420–2860 mm (Av. 2140 mm), corresponding to 90–180% (Av. 122%) of annual rainfall. The rate of deposition was higher at the mountain ridge and the forest edge than at the mountain side and the forest interior. Annual deposition of SO42−, NO3−, H+ and NH4+ from cloud water was estimated as 204, 153, 2.5 and 58 kg/ha, respectively, equivalent to 5.8–11.7 times the corresponding deposition via rain. The values are equal to, or exceed, the maximum deposition reported for Appalachian forests in the eastern United States. Multiple regression analyses indicate that cloud water deposition on to Cryptomeria canopies was significantly correlated with the following three parameters: cloud frequency, LWC, and wind speed. Thus, these three factors apparently control cloud water deposition on to forest canopies.

Study on Sampling Method of Rainfall, Throughfall, and Stemflow to Monitor the Effect of Acid Deposition on Forest Ecosystem

The use of samplers for rainfall, throughfall, and stemflow was studied in Chamaecyparis obtusa forest in Kobe to develop a suitable simplified collection method for long-term monitoring of the effect of acid deposition on the forest ecosystem. A filtrating bulk sampler, widely used in Japan due to its convenience, was modified for rainfall- and throughfall-sampling. The pH value, and concns. did not change within a two-week sampling period, and the collection efficiency of the modified type relative to the wet/dry sampler was 97% (mean). The three samplers (shampoo-hat, vinyl chloride tube, and gauze type) were used for stemflow sampling. Collection efficiency of the samplers was in the order of shampoo-hat> vinyl chloride tube> gauze and that of the gauze type varied significantly with rainfall condition.

Candidates to Provide a Specific Concentration Difference for Ambient Sulfur and Nitrogen Compounds Near the Coastal and Roadside Sites of Japan

The concentrations of atmospheric gases and aerosols were measured using the four-stage filter-pack method to study the atmospheric chemistry and the representativeness of a site established near an expressway and a national road with heavy traffic in a coastal as well as an urbanized area. The clear seasonal difference in the concentrations of nitrate species (HNO3 and NO3−) between the two sites was observed, and the difference was correlated with, but not quantitative, the atmospheric oxidation reaction from NO2 to HNO3. The concentrations of ammoniacal nitrogen (NH3 and NH4+) were determined on a regional scale; in other words, their concentrations were not determined by specific emission sources, differently from the case of nitrate species. The temporal variation of the concentration of total sulfur (SO2 + SO42−) was largely controlled by the concentration of SO2, which, in turn, would be controlled by emission sources other than roads, differently from the cases of nitrate species and ammoniacal nitrogen. It was strongly suggested that there was an existence of the important sulfur emission sources: one candidate is sea traffic lane.

Trans-boundary and in-country transport of air pollutants observed in Kobe, Japan by high frequent filter pack sampling method

The seasonal intensive sampling of gases and particulate matter in ambient air was conducted at the site established in urban area of Japan to study the seasonal difference of the temporal variation of gases and particulate matter concentrations in urban atmosphere as well as to illustrate the different transport regimes that impacts air pollutants. The sample was collected by the four-stage filter-pack method with 6-h interval for one week in four seasons (spring, summer, autumn and winter). The trans-boundary transport of air pollutants with high concentration was characteristically observed in the spring sampling. On the other hand, we could successfully detect the in-country transports of air pollutants in the summer sampling. Four-season’s intensive survey considered, we could show the characteristic transport of air pollutants to provide the episodic high concentration for ambient air in the urban area of Japan, and successfully illustrate the seasonal-dependent transport regimes to impact on air pollutants.