Deug-Soo Kim

Measurement of nitrogen oxide emissions from an agricultural soil with a dynamic chamber system

Biogenic soil emissions of nitric oxide (NO) were measured from an intensively managed agricultural row crop (corn, Zea mays) during a 4 week period (May 15 through June 9, 1995). The site was located in Washington County, near the town of Plymouth, which is in the Lower Coastal Plain of North Carolina. Soil NO flux was determined using a dynamic flowthrough chamber technique. The measurement period was characterized by two distinguishing features: an application of nitrogen (N) fertilizer at the midpoint of the experiment and a nontypical rainfall pattern. Average NO flux prior to the application of N fertilizer was 31.5 ± 10.1 ng N m−2 s−1, and more than doubled (77.7 ± 63.7 ng N m−2 s−1) after the application of a side-dressing of N fertilizer. Average soil extractable nitrogen values did not change significantly following application of the side-dressing of N fertilizer. We attribute this failure to detect a significant difference in soil extractable nitrogen following N fertilization to the method in which the fertilizer was applied, the subsequent rainfall pattern, and the technique of soil sampling. NO flux followed the same diurnal trend as soil temperature, with maximum NO emissions coinciding with maximum soil temperature, and minimum NO emissions coinciding with minimum soil temperature. NO flux was found to increase exponentially with soil temperature, but only after fertilization. Due to subsurface irrigation practices employed by the farmer, changes in soil water content were minimal, and no relation could be drawn between soil water content and NO flux. Simultaneous measurements of NOy, NO2, and NO emissions revealed that NO and NO2 emissions represent 86 and 8.7%, respectively, of NOy emissions leaving the soil. Simultaneous NO flux measurements made by a closed box flux technique, at the same site, revealed no statistically significant differences between the two different methodologies for measuring NO flux.

Trends and analysis of ambient NO, NOy, CO, and ozone concentrations in raleigh, north carolina

Ambient concentrations of NO and NOy as well as 03 and CO were measured during August 19 to September I, 1991 in downtown Raleigh, North Carolina as a part of the Southern Oxidants Study-southern Oxidants Research Program on Ozone Non-Attainment (SOS-SORP/ONA). These measurements were made in an effort to provide insight into the characteristics of nitrogen oxides and their role in the formation of ozone in the urban Southeast U.S. environment. NO and NOy showed bimodal diurnal variations with peaks in the morning (06:00 - 08:00 FAST) and in the hue evening (21:00 - 23:00 EST). These peaks at this urban site correspond to the coupled effects of rush hour traffic and meteorological conditions (i.e., variation of mixing height and dispersion conditions). The overall average NO and NOy concentrations were found to be 6.1 + 5.4 ppbv (range: 0 to 70 ppbv) and 14.9 + 8.1 ppbv (range: 0.3 to 110 ppbv), respectively. Average daily maxima of NO and NOy (18.3 ppbv and 27.4 ppbv) occurred during the morning. 03 showed a diurnal variation with a maximum in the afternoon between 14:00 and 16:00 EST; and a mean concentration 20 + 10 ppbv (range: 1 to 62 ppbv). Maximum 03 and CO concentrations during weekdays result ~om NO and CO emitted from mobile souw,~ during the morning rush hour. Background CO concentration at Raleigh was estimated to he ~ 470 :t: 52 ppbv. A linear correlation of r 2 = 0.53 between CO and NOy was observed. The ratio of CO to NOy (- 16) at the Raleigh site suggests that mobile sources are the major contributor to NO and NOy concentrations at the site.

Surface flux measurements of CO2 and N2O from a dried rice paddy in Japan during a fallow winter season.

Abstract The CO2 and N2O soil emissions at a rice paddy in Mase, Japan, were measured by enclosures during a fallow winter season. The Mase site, one of the AsiaFlux Network sites in Japan, has been monitored for moisture, heat, and CO2 fluxes since August 1999. The paddy soil was found to be a source of both CO2 and N2O flux from this experiment. The CO2 and N2O fluxes ranged from -27.6 to 160.4μg CO2/m2/sec (average of 49.1 ± 42.7 μg CO2/m2/sec) and from -4.4 to 129.5 ng N2O/m2/sec (average of 40.3 ± 35.6 ng N2O/m2/sec), respectively. A bimodal trend, which has a sub-peak in the morning around 10:00 a.m. and a primary peak between 2:00 and 3:00 p.m., was observed. Gas fluxes increased with soil temperature, but this temperature dependency seemed to occur only on the calm days. Average CO2 and N2O fluxes were 27.7 μg CO2/m2/sec and 13.4 ng N2O/m2/sec, with relatively small fluctuation during windy days, while averages of 69.3 μg CO2/m2/sec and 65.8 ng N2O/m2/sec were measured during calm days. This relationship was thought to be a result of strong surface winds, which enhance gas exchange between the soil surface and the atmosphere, thus reducing the gas emissions from soil surfaces.

OH reactivity in urban and suburban regions in Seoul, South Korea – an East Asian megacity in a rapid transition

South Korea has recently achieved developed country status with the second largest megacity in the world, the Seoul Metropolitan Area (SMA). This study provides insights into future changes in air quality for rapidly emerging megacities in the East Asian region. We present total OH reactivity observations in the SMA conducted at an urban Seoul site (May-June, 2015) and a suburban forest site (Sep, 2015). The total OH reactivity in an urban site during the daytime was observed at similar levels (∼15 s(-1)) to those previously reported from other East Asian megacity studies. Trace gas observations indicate that OH reactivity is largely accounted for by NOX (∼50%) followed by volatile organic compounds (VOCs) (∼35%). Isoprene accounts for a substantial fraction of OH reactivity among the comprehensive VOC observational dataset (25-47%). In general, observed total OH reactivity can be accounted for by the observed trace gas dataset. However, observed total OH reactivity in the suburban forest area cannot be largely accounted for (∼70%) by the trace gas measurements. The importance of biogenic VOC (BVOCs) emissions and oxidations used to evaluate the impacts of East Asian megacity outflows for the regional air quality and climate contexts are highlighted in this study.

Trends and analysis of ambient NO, NOy, CO, and ozone concentrations in Raleigh, North Carolina

Ambient concentrations of NO and NOy as well as 03 and CO were measured during August 19 to September I, 1991 in downtown Raleigh, North Carolina as a part of the Southern Oxidants Study-southern Oxidants Research Program on Ozone Non-Attainment (SOS-SORP/ONA). These measurements were made in an effort to provide insight into the characteristics of nitrogen oxides and their role in the formation of ozone in the urban Southeast U.S. environment. NO and NOy showed bimodal diurnal variations with peaks in the morning (06:00 08:00 FAST) and in the hue evening (21:00 23:00 EST). These peaks at this urban site correspond to the coupled effects of rush hour traffic and meteorological conditions (i.e., variation of mixing height and dispersion conditions). The overall average NO and NOy concentrations were found to be 6.1 + 5.4 ppbv (range: 0 to 70 ppbv) and 14.9 + 8.1 ppbv (range: 0.3 to 110 ppbv), respectively. Average daily maxima of NO and NOy (18.3 ppbv and 27.4 ppbv) occurred during the morning. 03 showed a diurnal variation with a maximum in the afternoon between 14:00 and 16:00 EST; and a mean concentration 20 + 10 ppbv (range: 1 to 62 ppbv). Maximum 03 and CO concentrations during weekdays result ~om NO and CO emitted from mobile souw,~ during the morning rush hour. Background CO concentration at Raleigh was estimated to he ~ 470 :t: 52 ppbv. A linear correlation of r 2 = 0.53 between CO and NOy was observed. The ratio of CO to NOy (16) at the Raleigh site suggests that mobile sources are the major contributor to NO and NOy concentrations at the site.