Measurements of ambient HONO concentrations and vertical HONO flux above a northern Michigan forest canopy

Abstract

Abstract. Systems have been developed and deployed at a North Michigan forested site to measure ambient HONO and vertical HONO flux. The modified HONO measurement technique is based on aqueous scrubbing of HONO using a coil sampler, followed by azo dye derivatization and detection using a long-path absorption photometer (LPAP). A Na 2 CO 3 -coated denuder is used to generate "zero HONO" air for background correction. The lower detection limit of the method, defined by 3 times of the standard deviation of the signal, is 1 pptv for 1-min averages, with an overall uncertainty of ± (1 + 0.05 [HONO]) pptv. The HONO flux measurement technique has been developed based on the relaxed eddy accumulation approach, deploying a 3-D sonic anemometer and two HONO measurement systems. The overall uncertainty is estimated to be within ± (8 × 10 −8 + 0.15 F HONO ) mol m −2 h −1 , with a 20-min averaged data point per 30 min. Ambient HONO and vertical HONO flux were measured simultaneously at the PROPHET site from 17 July to 7 August 2008. The forest canopy was found to be a net HONO source, with a mean upward flux of 0.37 × 10 −6 moles m −2 h −1 . The HONO flux reached a maximal mean of ∼ 0.7 × 10 −6 moles m −2 h −1 around solar noon, contributing a major fraction to the HONO source strength required to sustain the observed ambient concentration of ∼ 70 pptv. There were no significant correlations between [NO x ] and daytime HONO flux and between J NO 2 × [NO 2 ] and HONO flux, suggesting that NO x was not an important precursor responsible for HONO daytime production on the forest canopy surface in this low-NO x rural environment. Evidence supports the hypothesis that photolysis of HNO 3 deposited on the forest canopy surface is a major daytime HONO source.

Impact of HONO on global atmospheric chemistry calculated with an empirical parameterization in the EMAC model

“…However, in contrast to nighttime conditions, the HONO/NO x ratio during daytime is independent of HONO and NO x mixing ratios while it has a light dependency (given by j (NO 2 ), though with a low correlation coefficient (R 2 = 0.23). These results are in agreement with Zhang et al (2012), who showed that the daytime HONO flux does not correlate significantly with measured NO x mixing ratios, suggesting that under these conditions NO x is not an important precursor of HONO daytime formation. In addition, using the Community Multiscale Air Quality (CMAQ) model, Czader et al (2012) demonstrated that photochemical HONO formation can be a strong source during daytime, which directly impacts HO x and ozone levels.…”

“…It is worth mentioning that HONO measurements under very clean conditions, using wet-chemical techniques (other than LOPAP) have been reported to be biased by uncorrected interferences leading to artificially high HONO/NO x ratios Kleffmann and Wiesen, 2008;Su et al, 2008;Lu et al, 2010;Villena et al, 2011b;Zhang et al, 2012). Recent studies acknowledged this problem and corrected for these interferences (e.g., Su et al, 2008) or modified the technique to minimize them (e.g., Ren et al, 2010;Zhang et al, 2012). Under high NO x polluted conditions this problem is less pronounced (e.g., Kleffmann et al, 2006;Kleffmann and Wiesen, 2008).…”

“…During MCMA-2006, HONO was measured using LP-DOAS (Dusanter et al, 2009 and references therein), which selectively detects HONO based on it specific UV absorption, thus free of sampling artefacts and chemical interferences (Platt and Perner, 1980). During the New York campaign (Ren et al, 2003) HONO was measured by aqueousphase scrubbing and high performance liquid chromatography (HPLC) analysis , which has been used (also in a modified form) in several field measurement campaigns (e.g., Zhou et al, 2002;Ren et al, 2010;Zhang et al, 2012). It is worth mentioning that HONO measurements under very clean conditions, using wet-chemical techniques (other than LOPAP) have been reported to be biased by uncorrected interferences leading to artificially high HONO/NO x ratios Kleffmann and Wiesen, 2008;Su et al, 2008;Lu et al, 2010;Villena et al, 2011b;Zhang et al, 2012).…”

“…During the New York campaign (Ren et al, 2003) HONO was measured by aqueousphase scrubbing and high performance liquid chromatography (HPLC) analysis , which has been used (also in a modified form) in several field measurement campaigns (e.g., Zhou et al, 2002;Ren et al, 2010;Zhang et al, 2012). It is worth mentioning that HONO measurements under very clean conditions, using wet-chemical techniques (other than LOPAP) have been reported to be biased by uncorrected interferences leading to artificially high HONO/NO x ratios Kleffmann and Wiesen, 2008;Su et al, 2008;Lu et al, 2010;Villena et al, 2011b;Zhang et al, 2012). Recent studies acknowledged this problem and corrected for these interferences (e.g., Su et al, 2008) or modified the technique to minimize them (e.g., Ren et al, 2010;Zhang et al, 2012).…”

Impact of HONO on global atmospheric chemistry calculated with an empirical parameterization in the EMAC model

“…During MCMA-2006, HONO was measured using LP-DOAS (Dusanter et al, 2009 and references therein), which selectively detects HONO based on it specific UV absorption, thus free of sampling artefacts and chemical interferences (Platt and Perner, 1980). During the New York campaign (Ren et al, 2003) HONO was measured by aqueousphase scrubbing and high performance liquid chromatography (HPLC) analysis (Huang et al, 2002), which has been used (also in a modified form) in several field measurement campaigns (e.g., Zhou et al, 2002;Ren et al, 2010;Zhang et al, 2012). It is worth mentioning that HONO measurements under very clean conditions, using wet-chemical techniques (other than LOPAP) have been reported to be biased by uncorrected interferences leading to artificially high HONO/NO x ratios (Kleffmann et al, 2006;Kleffmann and Wiesen, 2008;Su et al, 2008;Lu et al, 2010;Villena et al, 2011b;Zhang et al, 2012).…”