A thermal dissociation laser‐induced fluorescence instrument for in situ detection of NO₂, peroxy nitrates, alkyl nitrates, and HNO₃

Abstract

[1] This paper describes a new instrument that uses a combination of thermal dissociation and laserinduced fluorescence detection of NO 2 for in situ detection of the sum total peroxy nitrates, the sum total of alkyl nitrates and hydroxyalkyl nitrates, and HNO 3 . The instrument is capable of routine, continuous in situ measurements of these three classes of compounds that are accurate (15%) with a low detection limit (90 parts per trillion (ppt) 10 s À1 , S/N ratio = 2 on a background of 1 ppb NO 2 and 30 ppt 10 s À1 on a background of 100 ppt NO 2 ). Theoretical analysis of potential interferences combined with laboratory experiments that test for interferences show that rapidly cooling the gas and dropping the pressure after the thermal dissociation reduces interferences to the order of 1 -5%. Observations in ambient air at the University of California Blodgett Forest Research Station demonstrate the capabilities of this instrument under field conditions. These field observations are compared with independent total NO y observations.

Observational Insights into Aerosol Formation from Isoprene

“…41 Gas phase nitric acid (HNO 3 ) was measured by CIMS in 2007 and laser induced fluorescence (LIF) in 2009. 42,43 NO 2 was measured at several heights during both campaigns using LIF 44,45 and in this work measurements from the 9.3 m height were used. In 2009, NO was also measured using a custom-built chemiluminescence instrument.…”

Real Time In Situ Detection of Organic Nitrates in Atmospheric Aerosols

“…The aerosol flow is then heated so that particles are vaporized to their gas phase precursors and detected using TD-LIF by which RONO 2 is thermally converted to RO + NO 2 and NO 2 is detected by LIF (10). A schematic of the instrument inlet system used in this study is shown in Figure 1.…”

“…Alkyl nitrates and nitric acid (HNO 3 ) are quantified by sampling through a heated inlet which thermally dissociates these molecules to NO 2 and a corresponding radical. The method has been compared to independent approaches for detection of NO 2 (28,29), total peroxy nitrates (ΣPN) (27) and ΣAN TD-LIF has previously been used to quantify various classes of gas + particle NO y by taking the difference in LIF signals measured with two inlets at two different temperatures (10). For the application described in this work, gas phase species including NO 2 are separated from particles before entering the heated portion of the inlet, and thus no subtraction is required.…”

The production and persistence of ΣRONO<sub>2</sub> in the Mexico City plume

“…NO 2 , PNs, and ANs were measured using the Berkeley thermal dissociation-laser induced fluorescence instrument (Thornton et al, 2000;Day et al, 2002). Briefly, gas is pulled simultaneously through four channels consisting of heated quartz tubes maintained at specific temperatures for the dissociation of each compound class above.…”

“…Here we present observations of ANs, measured by thermal dissociation coupled to laser-induced fluorescence detection of NO 2 (Thornton et al, 2000;Day et al, 2002), in and downwind of Mexico City using the NASA DC-8 platform during the Megacity Initiative: Local and Global Research Observations (MILAGRO) phase of the INTEX-B campaign in the spring of 2006 (Singh et al, 2009;Molina et al, 2010). The aircraft flights targeted plume evolution and crossed the Mexico City plume at its origin and at distances as far as 1000 km downwind.…”