Intercomparison of nitrous acid (HONO) measurement techniques in a megacity (Beijing)

Abstract

Nitrous acid (HONO) is a key determinant of the daytime radical budget in the daytime boundary layer, with quantitative measurement required to understand OH radical abundance. Accurate and precise measurements of HONO are therefore needed; however HONO is a challenging compound to measure in the field, in particular in a chemically complex and highly polluted environment. Here we report an inter-comparison exercise between HONO measurements performed by 30 two wet chemical techniques (the commercially available LOPAP and a custom-built instrument) and two Broadband Cavity Enhanced Absorption Spectrophotometer (BBCEAS) instruments at an urban location in Beijing. In addition, we report a comparison of HONO measurements performed by Time of Flight Chemical Ionization Mass Spectrometer (ToF-CIMS) andSyft Proton Transfer Reaction Mass Spectrometer (PTR-MS) to the more established techniques (wet chemical and BBCEAS).The key finding from the current work was that all instruments agree on the temporal trends / variability in HONO (r 2 >0.97), 35 yet displayed some divergence in absolute concentrations, with the wet chemical methods consistently higher than the BBCEAS systems by between 12 and 39%. We found no evidence for any systematic bias in any of the instruments, with the exception of measurements near instrument detection limits. The causes of the divergence in absolute HONO concentrations were unclear, and may in part have been due to spatial variability, i.e. differences in instrument location / inlet position.Atmos. Meas. Tech. Discuss., https://doi.

HONO Budget and Its Role in Nitrate Formation in the Rural North China Plain

“…Intercomparison in the NCP between various HONO measurement techniques also confirmed the reliability of LOPAP to quantify HONO in the polluted regions. 34,36,37 Other instruments for key-related species (VOCs, OVOCs, NO, NO2, NH3, O3, H2O2, CO, PM2.5, particle size distribution, and composition, etc.) and meteorological parameters (pressure, temperature, relative humidity (RH), J(NO2), etc.)…”

Ternary association reactions of H3O+, NO+ and O2+• with N2, O2, CO2 and H2O; implications for selected ion flow tube mass spectrometry analyses of air and breath

“…However, it should be noted that in some reported SIFT-MS studies very large sample flow rates were used (in order to enhance analytical sensitivity) when the above phenomenon must become more problematic. 4,5 In this major part of this study there are the primary ternary association reactions of three reagent ions, R + , with three different…”

Quantification of nitrous acid (HONO) and nitrogen dioxide (NO2) in ambient air by broadband cavity-enhanced absorption spectroscopy (IBBCEAS) between 361–388 nm

“…Photodissociation of HONO produces the hydroxyl radical (OH); this pathway can be a more important OH radical source (>10 times greater) than the photolysis of O3 to O( 1 D) and subsequent 25 reaction with water, especially in polluted urban environments (Harrison et al, 1996;Ren et al, 2006;Alicke et al, 2002). Despite the importance of HONO, accurate and time-resolved (i.e., < 5 min) in situ measurements of ambient HONO mixing ratios remain a challenge, exemplified by discrepancies reported among individual instruments in recent inter-comparison studies (Rodenas et al, 2013;Pinto et al, 2014;Crilley et al, 2019). These discrepancies arise in part as atmospheric HONO measurements by wet 30 chemical techniques or mass spectrometry require external calibration and are prone to interferences.…”

“…Other sources of systematic error in IBBCEAS instruments include the determination of the mirror reflectivity curve and, if purge gases are used to prevent contact of the sampled gas with the mirrors, the length over which the absorber is present (d0) compared to the total optical pathlength (d) (Duan et al, 2018). To exemplify these challenges, a recent inter-comparison study 60 (Crilley et al, 2019) has revealed significant biases in the retrieved mixing ratios between two modern IBBCEAS instruments, implying that IBBCEAS instruments must be validated.…”

“…An ongoing issue in the measurement of HONO in ambient air are measurement differences as those described in (Crilley et al, 2019) that are occasionally larger than expected from stated instrumental uncertainties. Mixing ratios measured by the IBBCEAS instrument described in this work were compared 365 with blue diode laser CRDS NO2 and TD-CRDS HONO and found in agreement.…”