Atmosphere-rice paddy exchanges of inorganic particles and relevant gases during a week in winter and a week in summer

Abstract

The aim of the present study was to investigate the air concentrations (mass concentration) and exchange fluxes of inorganic particles, i.e., water-soluble inorganic components in fine and coarse particles, and relevant gases at a paddy field for the single cropping of rice in central Japan. The target chemical species were ammonium (pNH 4 ), nitrate (pNO 3 ), nitrite (pNO 2 ), sulfate (pSO 4 ), and chloride (pCl) for inorganic particles separated into coarse and PM2.5 fractions and ammonia (NH 3 ), nitric acid (HNO 3 ), nitrous acid (HNO 2 ), sulfur dioxide (SO 2 ), and hydrochloric gas (HCl) for the relevant gases. Intensive observations were conducted for approximately one week in the winter of 2009 as a fallow season (winter 2009) and in the summer of 2010 at the heading stage of paddy rice (summer 2010). The filter-pack and gradient methods were used to determine the air concentrations and the exchange fluxes, respectively. The air concentrations of the coarse particles were lower than those of the PM2.5 except pCl and pNO 3 in the summer of 2010. The ion balance of PM2.5 implied an acidic condition in the daytime in summer 2010 but neutral conditions at other times. Ammonia showed the highest air concentrations and the largest exchange fluxes in most cases among all target species. The paddy field was usually a sink for the inorganic particles and relevant gases; however, NH 3 emission in the summer of 2010, perhaps from the paddy rice, occasionally occurred when the air concentrations of NH 3 became very low.

Four-year monitoring of atmospheric ammonia using passive samplers at a single-crop rice paddy field in central Japan

“…The study site is situated in a rural area typical of this region, composed of arable land (mainly rice paddies), small forests, and residential areas. Single cropping of rice is performed in this region, and the typical management practices have been described in Hayashi et al (2012). The periods of cropping and fallow seasons in the study period from May 2007 to April 2011 are listed in Table 1 together with the mean air temperature and the total precipitation during each period.…”

“…Therefore, it is possible that the role of Japanese paddy fields as a sink of atmospheric NH 3 has recently increased. Hayashi et al (2012) demonstrated the importance of NH 3 in the atmosphere-rice paddy exchange through intensive observations over two weeks. Long-term monitoring is required to elucidate the seasonal patterns and the annual balance of atmosphere-rice paddy exchanges of NH 3 .…”

“…Hayashi et al (2012) showed that ammonia (NH 3 ) was the most important chemical species among inorganic gases and relevant inorganic particles in terms of both the air concentration and the exchange flux.…”

“…However, a resistance model (e.g., Hicks et al, 1987) or a gradient method (e.g., Hayashi et al, 2012) can be applied even with poor time resolution. The resistance model is a simple method for determining the deposition velocity in which the air concentration of the target substance at a single height is used to determine the deposition flux.…”

Development of an onsite computation scheme of eddy-covariance fluxes

“…The EC technique enables us to quantify not only ET but also fluxes of greenhouse gases such as CO 2 , CH 4 , and N 2 O and even NH 3 (Hayashi et al, 2013) and pSO 4 (Hayashi et al, 2012) in combination with the improved aerodynamic method (Miyata et al, 2000). Nevertheless, real-time flux monitoring by the EC technique remains challenging, because the final fluxes must be extracted from large turbulent fluctuation datasets, demanding large computational resources.…”