Abstract
AbstractFollowing measurements in the winter of 2012, formic acid (HCOOH) and nitric acid (HNO3) were measured using a chemical ionization mass spectrometer (CIMS) during the Summer Clean Air for London (ClearfLo) campaign in London, 2012. Consequently, the seasonal dependence of formic acid sources could be better understood. A mean formic acid concentration of 1.3 ppb and a maximum of 12.7 ppb was measured which is significantly greater than that measured during the winter campaign (0.63 ppb and 6.7 ppb, respectively). Daily calibrations of formic acid during the summer campaign gave sensitivities of 1.2 ion counts s−1 parts per trillion (ppt) by volume−1 and a limit of detection of 34 ppt. During the summer campaign, there was no correlation between formic acid and anthropogenic emissions such as NOx and CO or peaks associated with the rush hour as was identified in the winter. Rather, peaks in formic acid were observed that correlated with solar irradiance. Analysis using a photochemical trajectory model has been conducted to determine the source of this formic acid. The contribution of formic acid formation through ozonolysis of alkenes is important but the secondary production from biogenic VOCs could be the most dominant source of formic acid at this measurement site during the summer.
Highlights
IntroductionThe most abundant being formic acid (HCOOH), are ubiquitous in the troposphere
Organic acids, the most abundant being formic acid (HCOOH), are ubiquitous in the troposphere
Isoprene measurements were made using a dual channel GC-flame ionization detector and was operated by the National Centre for Atmospheric Science (NCAS) Facility for Ground Atmospheric Measurements (FGAM) ( the Atmospheric Measurements Facility (AMF)) with the instrument set up and calibration described in Hopkins et al (2003) and its deployment during ClearfLO described in detail by Dunmore et al (2015)
Summary
The most abundant being formic acid (HCOOH), are ubiquitous in the troposphere. Other known sources of formic acid nonexhaustively include primary emissions from biogenic and anthropogenic activity, secondary production via alkene ozonolysis (Sanhueza et al, 1996), acetaldehyde tautomerization to vinyl alcohol, followed by reaction with OH (Andrews et al, 2012; Millet et al, 2015), biomass burning (Andreae & Merlet, 2001; R’Honi et al, 2013), and photodegradation of secondary organic aerosol (Malecha & Nizkorodov, 2016). The winter study presented no evidence of production from biogenic or secondary photochemical pathways but demonstrated that direct anthropogenic emissions were the dominant source of formic acid at this time and location. Global modeling using the emission factors derived from London during winter suggested that in the northern midlatitudes, around major urban centers, the contribution of formic acid from direct emissions at particular locations (Northern Europe) can reach up to 30% (Bannan et al, 2014). This study will compare the results of formic acid production from winter (January to February 2012; Bannan et al, 2014) with the summer (July to August 2012) as part of the Clean Air for London (ClearfLo) campaign to assess the importance of seasonality to formic acid production at this location
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