Evaluation of MEGAN predicted biogenic isoprene emissions at urban locations in Southeast Texas

• Published in: Atmospheric environment (1994) Vol. 110; pp. 54 - 64
• Main Authors: Kota, Sri Harsha, Schade, Gunnar, Estes, Mark, Boyer, Doug, Ying, Qi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2015
• Subjects: 2006 TexAQS; Biogenic emissions; Community Multiscale Air Quality (CMAQ) model; Isoprene; Model of Emissions of Gases and Aerosols from Nature (MEGAN); Source apportionment; ASW, USA, Texas; USA, Texas, Houston; Model of Emissions of Gases and Aerosols from Nature (MEGAN); 2006 TexAQS; Biogenic emissions; Source apportionment; Isoprene; Community Multiscale Air Quality (CMAQ) model
• ISSN: 1352-2310; 1873-2844
• DOI: 10.1016/j.atmosenv.2015.03.027

Summertime isoprene emissions in the Houston area predicted by the Model of Emissions of Gases and Aerosol from Nature (MEGAN) version 2.1 during the 2006 TexAQS study were evaluated using a source-oriented Community Multiscale Air Quality (CMAQ) Model. Predicted daytime isoprene concentrations at nine surface sites operated by the Texas Commission of Environmental Quality (TCEQ) were significantly higher than local observations when biogenic emissions dominate the total isoprene concentrations, with mean normalized bias (MNB) ranges from 2.0 to 7.7 and mean normalized error (MNE) ranges from 2.2 to 7.7. Predicted upper air isoprene and its first generation oxidation products of methacrolein (MACR) and methyl vinyl ketone (MVK) were also significantly higher (MNB = 8.6, MNE = 9.1) than observations made onboard of NOAA's WP-3 airplane, which flew over the urban area. Over-prediction of isoprene and its oxidation products both at the surface and the upper air strongly suggests that biogenic isoprene emissions in the Houston area are significantly overestimated. Reducing the emission rates by approximately 3/4 was necessary to reduce the error between predictions and observations. Comparison of gridded leaf area index (LAI), plant functional type (PFT) and gridded isoprene emission factor (EF) used in MEGAN modeling with estimates of the same factors from a field survey north of downtown Houston showed that the isoprene over-prediction is likely caused by the combined effects of a large overestimation of the gridded EF in urban Houston and an underestimation of urban LAI. Nevertheless, predicted ozone concentrations in this region were not significantly affected by the isoprene over-predictions, while predicted isoprene SOA and total SOA concentrations can be higher by as much as 50% and 13% using the higher isoprene emission rates, respectively. •CMAQ over-predicted isoprene concentrations using MEGAN generated emissions.•Predicted isoprene oxidation products, MACR and MVK, were higher than observations.•MEGAN significantly over-predicted isoprene concentrations in urban Houston area.•Gridded EF of isoprene in urban Houston area in MEGAN input was overestimated.