Sensitivity of nitrate aerosols to ammonia emissions and to nitrate chemistry: implications for present and future nitrate optical depth
We update and evaluate the treatment of nitrate aerosols in the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model (AM3). Accounting for the radiative effects of nitrate aerosols generally improves the simulated aerosol optical depth, although nitrate concentrations at the surface ar...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/1459/2016/acp-16-1459-2016.pdf |
| Summary: | We update and evaluate the treatment of nitrate aerosols in the
Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model
(AM3). Accounting for the radiative effects of nitrate aerosols
generally improves the simulated aerosol optical depth, although
nitrate concentrations at the surface are biased high. This bias can
be reduced by increasing the deposition of nitrate to account for
the near-surface volatilization of ammonium nitrate or by neglecting
the heterogeneous production of nitric acid to account for the
inhibition of N<sub>2</sub>O<sub>5</sub> reactive uptake at high nitrate
concentrations. Globally, uncertainties in these processes can
impact the simulated nitrate optical depth by up to 25 %, much
more than the impact of uncertainties in the seasonality of ammonia
emissions (6 %) or in the uptake of nitric acid on dust
(13 %). Our best estimate for fine nitrate optical
depth at 550 nm in 2010 is 0.006 (0.005–0.008). In wintertime, nitrate aerosols
are simulated to account for over 30 % of the aerosol optical depth over
western Europe and North America. Simulated nitrate optical depth increases
by less than 30 % (0.0061–0.010) in response to projected changes in
anthropogenic emissions from 2010 to 2050 (e.g., −40 % for SO<sub>2</sub> and
+38 % for ammonia). This increase is primarily driven by greater
concentrations of nitrate in the free troposphere, while surface nitrate
concentrations decrease in the midlatitudes following lower concentrations of
nitric acid. With the projected increase of ammonia emissions, we show that
better constraints on the vertical distribution of ammonia (e.g., convective transport
and biomass burning injection) and on the sources and sinks of nitric acid
(e.g., heterogeneous reaction on dust) are needed to improve estimates of
future nitrate optical depth. |
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| ISSN: | 1680-7316 1680-7324 |