Observations of Nitrogen Oxides Diurnal Variations and Eddy Covariance Fluxes above a Mixed Hardwood Forest during the 2016 PROPHET-AMOS Campaign
Abstract
Nitrogen oxides (NOx = NO + NO2) are important constituents in the atmosphere because they can control ozone production and undergo oxidation reactions with other species. Deposition and emission of NOx can impact the ecosystem by influencing the nitrogen cycle, vegetation health and forest carbon storage. Exchange of NOx between the atmosphere and biosphere is poorly understood due to a lack of direct observations. Here, we present results of nitrogen oxides observations and eddy covariance fluxes above a forest from the 2016 PROPHET-AMOS summer field campaign using a custom built AQD NOxy instrument. This field site is in a mixed deciduous and coniferous forest located in northern Michigan, with a research tower available for above-canopy measurements. Observations made at 29 m show the mixing ratio of NO and NO2 ranges from 0 to 640 ppt and 68 to 3600 ppt respectively. The night-time NO mixing ratio is close to zero, while NO2 builds up to a median of around 700 ppt. A maximum mixing ratio of NO resulting from photolysis of NO2 is frequently observed in the early morning. Median midday NO and NO2 mixing ratios are 50 ppt and 500 ppt. Fluxes calculated by eddy covariance showed an upward flux of NO2 and a downward flux of NO, which is an example of chemical flux divergence due to fast chemistry and diminished solar radiation below the canopy. Daytime fluxes of NO and NO2 peak at similar times in the morning, resulting in a net downward NOx flux with a maximum around 2.5 ppt m/s. To better explain NOx flux observations in this forest, results are compared to previous measurements of the total deposition budget of reactive nitrogen oxides, as well as results from 1-D canopy model FORCAsT.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.A51B2049S
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES