Impacts of HONO sources on the photochemistry in Mexico City during the MCMA-2006/MILAGO Campaign
Atmospheric Chemistry and Physics
The contribution of HONO sources to the photochemistry in Mexico City is investigated during the MCMA-2006/MILAGO Campaign using the WRF-CHEM model. Besides the homogeneous reaction of NO with OH, four additional HONO sources are considered in the WRF-CHEM model: secondary HONO formation from NO 2 heterogeneous 5 reaction with semivolatile organics, NO 2 reaction with freshly emitted soot, NO 2 heterogeneous reaction on aerosol and ground surfaces. The WRF-CHEM model with the five HONO sources
... five HONO sources performs reasonably well in tracking the observed diurnal variation of HONO concentrations. The HONO sources included are found to significantly improve the HO x (OH+HO 2 ) simulations during daytime and the partition of NO/NO 2 in 10 15 aerosol concentrations by a factor of 2 on average in the morning, although contribute less during the rest of the day. The simulated nitrate and ammonium aerosols are also remarkably enhanced in the morning when the four HONO sources are added, in good agreement with the measurements. The impact of the HONO sources on the sulfate aerosols is negligible because of the inefficient conversion of H 2 SO 4 from SO 2 reacting 20 with OH. most air pollutants (e.g.Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion Alicke et al. (2002; 2003) found that the photolysis of HONO produced up to 34% of the total OH formed during a 24-h period during BERLIOZ in Germany. Volkamer et al. (2007) also showed that photo-induced HONO sources made an important contribution to the OH level in the early morning during the MCMA-2003 field campaign in Mexico City. 5 25 HONO did not contribute significantly to summertime O 3 concentrations of polluted air masses. Furthermore, Aumont et al. (2003) conducted simulations with a two-layer box model to verify the impact of the photolysis of HONO on the NO x /HO x /O 3 chemistry in the polluted boundary layer. Three HONO sources were added in their simulations, 4146 ACPD 10, 4143-4188, 2010 Abstract 20 4150 Abstract 25 4155 Abstract 10, 4143-4188, 2010 Abstract 10, 4143-4188, 2010 Abstract 10, 4143-4188, 2010 Abstract 10, 4143-4188, 2010 Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 30 ogy using cluster analysis, Atmos. Abstract Faraday Discuss , 130, 195-210, 2005.