Airborne formaldehyde and volatile organic compound measurements over the Daesan petrochemical complex on Korea’s northwest coast during the Korea-United States Air Quality study

Abstract

The U.S. National Aeronautics and Space Administration in partnership with Korea’s National Institute of Environmental Research embarked on the Korea-United States Air Quality (KORUS-AQ) study to address air quality issues over the Korean peninsula. Underestimation of volatile organic compound (VOC) emissions from various large facilities on South Korea’s northwest coast may contribute to this problem, and this study focuses on quantifying top-down emissions of formaldehyde (CH2O) and VOCs from the largest of these facilities, the Daesan petrochemical complex, and comparisons with the latest emission inventories. To accomplish this and additional goals discussed herein, this study employed a number of measurements acquired during KORUS-AQ onboard the NASA DC-8 aircraft during three Daesan overflights on June 2, 3, and 5, 2016, in conjunction with a mass balance approach. The measurements included fast airborne measurements of CH2O and ethane from an infrared spectrometer, additional fast measurements from other instruments, and a suite of 33 VOC measurements acquired by the whole air sampler. The mass balance approach resulted in consistent top-down yearly Daesan VOC emission flux estimates, which averaged (61 ± 14) × 103 MT/year for the 33 VOC compounds, a factor of 2.9 ± 0.6 (±1.0) higher than the bottom-up inventory value. The top-down Daesan emission estimate for CH2O and its four primary precursors averaged a factor of 4.3 ± 1.5 (± 1.9) times higher than the bottom-up inventory value. The uncertainty values in parentheses reflect upper limits for total uncertainty estimates. The resulting averaged top-down Daesan emission estimate for sulfur dioxide (SO2) yielded a ratio of 0.81–1.0 times the bottom-up SO2 inventory, and this provides an important cross-check on the accuracy of our mass balance analysis.

Evolution of formaldehyde (HCHO) in a plume originating from a petrochemical industry and its volatile organic compounds (VOCs) emission rate estimation

“…The May 22 HKA and DC-8 flights focused on sampling the chemical evolution of the DPC plume in the far-field outflow. Consequently, the initial mole fractions of all chemical species and photolysis frequencies in the model, depicting the near-field character of DPC emissions, were constrained with June 5 DC-8 observations close to the emissions source, as listed in Table S1 (see Section 3.2.3; Fried et al, 2020). To account for diluting effects of the constrained species, we apply first-order dilution with a rate coefficient of 1.3 Â 10 -5 s -1 calculated by the dispersion of CO (see Section 3.2.2).…”

“…During the June 5 flight, the DC-8 circled around the DPC area to capture fresh emissions (approximately less than 7 min. of air processing time, Fried et al, 2020) coded by ethene mole fraction). The wind direction during the flight was mainly northeasterly, thus the DC-8 was able to sample DPC emissions as a single outflow plume.…”

“…Table S1 shows the chemical species used in this study and their average mole fractions as well as the initial conditions for our model run. We are assuming that the DPC VOC emissions speciation and rates did not drastically differ for the two sampling days-May 22 and June 5-since it is a large facility where yearly production lines operate as Fried et al (2020) describe; VOC emission rates from the DPC on 3 different days during the mission are consistent within 23% from their mass balanced approach. However, the relative fraction of captured VOCs mole fraction against the total VOC emission rate on those 2 days likely differs due to the difference in atmospheric stability and any offset of the sampling location with respect to the center of the plume.…”

“…For a conservative estimate in VOC emissions, we assume that HCHO observed over the DPC by the DC-8 is directly emitted from the stacks with minimal contribution from secondary HCHO; a sensitivity test of the possible contribution of secondary HCHO production is performed in Section 4. During the flight, high HCHO mole fractions up to 16 ppb (median: 10.3 ppb) were observed by Compact Airborne Multi-species Spectrometer over the DPC (Fried et al, 2020). Thus, the observed median HCHO mole fraction (10.3 ppb) over the DPC was considered as primary HCHO in the model, while the 2.7 ppb HCHO measured upwind (4 km from DPC) was set as model background.…”

“…A mass balance approach with airborne measurements can also be used to quantify the emissions from point sources (White, 1976;Cambaliza et al, 2014;Peischl et al, 2015). In fact, a recent study done by Fried et al (2020) employed this method (for the same facility in this study). However, as discussed in that paper, this method requires corrected and/or uncorrected timeresolved airborne observations of discrete but full coverage of speciated VOCs, as well as continuous high time resolution VOCs to ensure complete plume sampling.…”