Evaluating high-resolution forecasts of atmospheric CO and CO2 from a global prediction system during KORUS-AQ field campaign
Authors: Tang Wenfu , Arellano Avelino F. , DiGangi Joshua P. , Choi Yonghoon , Diskin Glenn S. , Agustí-Panareda Anna , Parrington Mark , Massart Sebastien , Gaubert Benjamin , Lee Youngjae , Kim Danbi , Jung Jinsang , Hong Jinkyu , Hong Je-Woo , Kanaya Yugo , Lee Mindo , Stauffer Ryan M. , Thompson Anne M. , Flynn James H. , Woo Jung-Hun 
Published: August 2018

Abstract. Accurate and consistent monitoring of anthropogenic combustion is
imperative because of its significant health and environmental impacts,
especially at city-to-regional scale. Here, we assess the performance of the
Copernicus Atmosphere Monitoring Service (CAMS) global prediction system
using measurements from aircraft, ground sites, and ships during the
Korea-United States Air Quality (KORUS-AQ) field study in May to June 2016. Our
evaluation focuses on CAMS CO and CO2 analyses as well as two
higher-resolution forecasts (16 and 9 km horizontal resolution) to assess their
capability in predicting combustion signatures over east Asia. Our results
show a slight overestimation of CAMS CO2 with a mean bias against
airborne CO2 measurements of 2.2, 0.7, and 0.3 ppmv for 16 and
9 km CO2 forecasts, and analyses, respectively. The positive
CO2 mean bias in the 16 km forecast appears to be consistent
across the vertical profile of the measurements. In contrast, we find a
moderate underestimation of CAMS CO with an overall bias against airborne CO
measurements of −19.2 (16 km), −16.7 (9 km), and −20.7 ppbv
(analysis). This negative CO mean bias is mostly seen below 750 hPa for all
three forecast/analysis configurations. Despite these biases, CAMS shows a
remarkable agreement with observed enhancement ratios of CO with
CO2 over the Seoul metropolitan area and over the West (Yellow) Sea, where
east Asian outflows were sampled during the study period. More efficient
combustion is observed over Seoul
(dCO/dCO2=9 ppbv ppmv−1) compared to the West Sea
(dCO/dCO2=28 ppbv ppmv−1). This
“combustion signature contrast” is consistent with previous studies in
these two regions. CAMS captured this difference in enhancement ratios
(Seoul: 8–12 ppbv ppmv−1, the West Sea: ∼30 ppbv ppmv−1)
regardless of forecast/analysis configurations. The correlation of CAMS CO
bias with CO2 bias is relatively high over these two regions
(Seoul: 0.64–0.90, the West Sea: ∼0.80) suggesting that the contrast
captured by CAMS may be dominated by anthropogenic emission ratios used in
CAMS. However, CAMS shows poorer performance in terms of capturing
local-to-urban CO and CO2 variability. Along with measurements at
ground sites over the Korean Peninsula, CAMS produces too high CO and
CO2 concentrations at the surface with steeper vertical gradients
(∼0.4 ppmv hPa−1 for CO2 and 3.5 ppbv hPa−1 for
CO) in the morning samples than observed (∼0.25 ppmv hPa−1 for
CO2 and 1.7 ppbv hPa−1 for CO), suggesting weaker boundary
layer mixing in the model. Lastly, we find that the combination of CO
analyses (i.e., improved initial condition) and use of finer resolution
(9 km vs. 16 km) generally produces better forecasts.