Using an Inverse Model to Reconcile Differences in Simulated and Observed Global Ethane Concentrations and Trends Between 2008 and 2014
Abstract
Ethane (C2H6) is the most abundant nonmethane hydrocarbon (NMHC) in the troposphere and plays an important role in atmospheric chemistry. In the presence of nitrogen oxides (NOx), emissions of C2H6 can result in the production of ozone (O3), which is detrimental to human health, can decrease crop yields, and has a positive (warming) radiative effect on the climate. We use a global model, TOMCAT, and an inverse model, INVICAT, to estimate emissions of C2H6 between 2008 and 2014 by assimilating surface flask observations. We find that baseline global emissions in 2008 need to increase by a factor of 2.04-2.11 in order for the model to capture C2H6 observations, indicating large biases in current emission inventories. Most of this increase occurs over North America and Eurasia, with temperate North American emissions accounting for 23-26% of the total global emission increase and temperate Eurasian emissions accounting for 35-37%. Further to this, recent peer-reviewed analysis of long-term observational records shows an increase in C2H6 in the Northern Hemisphere since ∼2009. Our results indicate that annual global emissions of C2H6 have increased at a rate of 0.27 ± 0.54-0.33 ± 0.44 Tg/yr2 between 2008 and 2014. A statistically significant positive trend of 0.20 ± 0.11-0.24 ± 0.13 Tg/yr2 (p ≤ 0.01) is found in temperate North America, resulting in emissions that are 31-32% larger in 2014 than in 2008. We also evaluated the effect of the improved C2H6 emissions on other chemical species using the TOMCAT full chemistry model. The near doubling of the C2H6 emissions led to increases in acetaldehyde (CH3CHO), peroxyacetyl nitrate (PAN), and O3. Several models have shown negative biases in CH3CHO and improving C2H6 emissions may offer some improvements in the simulation of this species. We used methane-to-ethane emission ratios (MERs) calculated from observations made near oil and natural gas production facilities to find that that methane emissions in the United States could have increased simultaneously at a rate of 2.18 ± 1.09 Tg/yr2 between 2008 and 2014. Our results corroborate previous studies' conclusions that a rapid increase in oil and natural gas production in United States over this time period is likely a large driver of the change in emissions.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2019
- Bibcode:
- 2019EGUGA..2117031W