Reply on RC1

Albert Ruth

doi:10.5194/amt-2021-291-ac1

Abstract

Abstract. An instrument based on 20âm open-path incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) was established at the JÃ¼lich SAPHIR chamber in spring 2011. The setup was optimized for the detection of HONO and NO2 in the near-UV region 352â386ânm, utilizing a bright hot-spot Xe-arc lamp and a UV-enhanced charge-coupled device (CCD) detector. A 2Ï detection limit of 26âpptv for HONO and 76âpptv for NO2 was achieved for an integration time of 1âmin. Methacrolein (MACR) was also detected at mixing ratios below 5âppbv with an estimated 2Ï detection limit of 340âpptv for the same integration time. The IBBCEAS instrument's performance for HONO and NO2 detection was compared to that of extractive wet techniques, long-path absorption photometry (LOPAP), and chemiluminescence spectrometry (CLS) NOx detection, respectively. For the combined data sets an overall good agreement for both trend and absolute mixing ratios was observed between IBBCEAS and these established instruments at SAPHIR. Correlation coefficients r for HONO range from 0.930 to 0.994 and for NO2 from 0.937 to 0.992. For the single measurement of MACR r=0.981 is found in comparison to proton-transfer-reaction mass spectrometry (PTRMS).

Highlights

Photolysis of nitrous acid (HONO + h ( < 400 nm OH + NO) leads to the formation of the most important daytime 25 oxidant in the atmosphere, the hydroxyl radical (OH)
Measurements of time-dependent mixing ratios of HONO, NO2 and MACR using open-path incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) were taken during Summer and Autumn 2011, and compared with those utilizing long-path absorption photometry (LOPAP), chemiluminescence 190 spectrometry (CLS) and proton transfer reaction mass spectrometry (PTRMS), respectively
After cleaning and humidifying the SAPHIR chamber HONO formation by unknown photo-induced reactions on the Teflon chamber walls and degradation was studied in experiments always including light-induced and dark reactions of HONO formation or destruction – the experimental protocols 200 concerning changes in chamber conditions are given in the figure captions

Summary

Introduction

Photolysis of nitrous acid (HONO + h ( < 400 nm OH + NO) leads to the formation of the most important daytime 25 oxidant in the atmosphere, the hydroxyl radical (OH). HONO indirectly affects the oxidative potential of the troposphere and strongly influences degradation mechanisms of a vast variety of natural and urban pollutants. The mechanisms of HONO formation in the troposphere are still not fully understood (Calvert et al 1994, Finlayson-Pitts et al 2003, Ramazan et al 2004, Liu et al 2019). Many atmospheric studies revealed elevated HONO mixing ratios during daytime under specific conditions that cannot be fully explained (Staffelbach et al 1997, Zhou et al 2002a, Zhou et al 2003, Kleffmann et al 2003, Vogel et al 30 2003, Kleffmann et al 2005, Acker et al 2006, Spataro and Ianniello, 2014).

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Discussion

Conclusion