Comparison of formaldehyde tropospheric columns in Australia and New Zealand using MAX-DOAS, FTIR and TROPOMI

Abstract

Abstract. South-eastern Australia has been identified by modelling studies as a hotspot of biogenic volatile organic compound (VOC) emissions; however, long-term observational VOC studies are lacking in this region. Here, 2.5 years of multi-axis differential optical absorption spectroscopy (MAX-DOAS) formaldehyde (HCHO) measurements in Australasia are presented, from Broadmeadows, in northern Melbourne, Australia, and from Lauder, a rural site in the South Island of New Zealand. Across the measurement period from December 2016 to November 2019, the mean formaldehyde columns measured by the MAX-DOAS were 2.50±0.61×1015 molec. cm−2 at Lauder and 5.40±1.59×1015 molec. cm−2 at Broadmeadows. In both locations, the seasonal cycle showed a pronounced peak in Austral summer (December–January–February) consistent with temperature-dependent formaldehyde production from biogenic precursor gases. The amplitude of the seasonal cycle was 0.7×1015 molec. cm−2 at Lauder, and it was 2.0×1015 molec. cm−2 at Broadmeadows. The Lauder MAX-DOAS HCHO measurements are compared with 27 months of co-located Fourier transform infrared (FTIR) observations. The seasonal variation of Lauder MAX-DOAS HCHO, smoothed by the FTIR averaging kernels, showed good agreement with the FTIR measurements, with a linear regression slope of 1.03 and an R2 of 0.66 for monthly averaged formaldehyde partial columns (0–4 km). In addition to ground-based observations, a clear way to address the VOC measurement gap in areas such as Australasia is with satellite measurements. Here, we demonstrate that the TROPOspheric Monitoring Instrument (TROPOMI) can be used to distinguish formaldehyde hotspots in forested and agricultural regions of south-eastern Australia. The MAX-DOAS measurements are also compared to TROPOMI HCHO vertical columns at Lauder and Melbourne; very strong monthly average agreement is found for Melbourne (regression slope of 0.61 and R2 of 0.95) and a strong agreement is found at Lauder (regression slope of 0.73 and R2 of 0.61) for MAX-DOAS vs. TROPOMI between May 2018 and November 2019. This study, the first long-term satellite comparison study using MAX-DOAS in the Southern Hemisphere, highlights the improvement offered by TROPOMI's high resolution over previous satellite products and provides the groundwork for future studies using ground-based and satellite DOAS for studying VOCs in Australasia.

Measurement Report: MAX-DOAS measurements characterise Central London ozone pollution episodes during 2022 heatwaves

“…Uncertainties in the dSCDs calculated by DOASIS are relatively small (<5%) for all three trace gases. This is as expected for urban MAX-DOAS NO 2 and O 4 Ortega et al, 2015), but lower than is typical for urban MAX-DOAS HCHO (Benavent et al, 2019;Heckel et al, 2005;Ryan et al, 2020b). This may be because HCHO dSCDs in Central London are three times larger than those over Melbourne, Australia in Ryan et al (2020b) and due to differences in HCHO wavelength ranges used by Heckel et al (2005) and Benavent et al (2019).…”

“…The software corrects the raw spectra for dark current, electronic offset and stray light and convolves spectral cross sections of the analysed trace gases with the slit function of the instrument. Optimized wavelength ranges are 338-370 nm for NO2 and the O 2 -O 2 dimer (O 4 ), as recommended following a recent MAX-DOAS intercomparison campaign (Kreher et al, 2020), and 324.5-359 nm for HCHO, as this yields lower relative dSCD fit errors than the other commonly used fit range of 336-359 nm (Ryan et al, 2020b). O 4 is used to constrain aerosol impacts on the atmospheric light path.…”

“…October 2017 and passes overhead each day at about 13:30 local solar time (LST). TROPOMI has a ground pixel size of 5.5 TROPOMI pixel centres are commonly sampled 0.2° around the geographic coordinates of MAX-DOAS instruments for intercomparison of the two (Marais et al, 2021b;Pinardi et al, 2020;Ryan et al, 2020b). Instead, we use a location roughly halfway between the MAX-DOAS instrument and the visible horizon to account for its southeast viewing direction (Figure 1).…”

Comparative assessment of TROPOMI and OMI formaldehyde observations and validation against MAX-DOAS network column measurements

“…where N is the number of collocated pairs (days or months). We also derive correlation, slope and offset of the linear regression using the robust Theil-Sen estimator (Sen, 1968) as done in Vigouroux et al (2020).…”

Formaldehyde Exposure Racial Disparities in Southeast Texas

“…Daily satellite measurements have found that HCHO concentrations follow a spatial distribution similar to biogenic sources in the US, implying that biogenic emissions are a major source of HCHO. Biogenic sources emit isoprene that reacts in the atmosphere to form HCHO. − More than 90% of the HCHO associated with biogenic sources forms through this secondary reaction pathway. ,,− Identification of other HCHO sources using satellites is challenging. Most satellite studies average concentrations over weeks or months in order to remove the noise in the measurements.…”