Vertical profiles of NO<sub>2</sub>, SO<sub>2</sub>, HONO, HCHO, CHOCHO and aerosols derived from MAX-DOAS measurements at a rural site in the central western North China Plain and their relation to emission sources and effects of regional transport

Abstract

Abstract. A multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument was deployed in May and June 2016 at a monitoring station (37.18∘ N, 114.36∘ E) in the suburban area of Xingtai, which is one of the most polluted cities in the North China Plain (NCP), during the Atmosphere-Aerosol-Boundary Layer-Cloud (A2BC) experiment and Air chemistry Research In Asia (ARIAs) joint experiments to derive tropospheric vertical profiles of NO2, SO2, HONO, HCHO, CHOCHO and aerosols. Aerosol optical depths derived from MAX-DOAS were found to be consistent with collocated sun-photometer measurements. Also the derived near-surface aerosol extinction and HCHO mixing ratio agree well with the coincident visibility meter and in situ HCHO measurements, with mean HCHO near-surface mixing ratios of ∼3.5 ppb. Underestimations of MAX-DOAS results compared to in situ measurements of NO2 (∼60 %) and SO2 (∼20 %) are found expectedly due to vertical and horizontal inhomogeneity of trace gases. Vertical profiles of aerosols and NO2 and SO2 are reasonably consistent with those measured by a collocated Raman lidar and aircraft spirals over the station. The deviations can be attributed to differences in sensitivity as a function of altitude and substantial horizontal gradients of pollutants. Aerosols, HCHO and CHOCHO profiles typically extended to higher altitudes (with 75 % integrated column located below ∼1.4 km) than NO2, SO2 and HONO did (with 75 % integrated column below ∼0.5 km) under polluted conditions. Lifted layers were systematically observed for all species (except HONO), indicating accumulation, secondary formation or long-range transport of the pollutants at higher altitudes. Maximum values routinely occurred in the morning for NO2, SO2 and HONO but occurred at around noon for aerosols, HCHO and CHOCHO, mainly dominated by photochemistry, characteristic upslope–downslope circulation and planetary boundary layer (PBL) dynamics. Significant day-to-day variations are found for all species due to the effect of regional transport and changes in synoptic pattern analysed with the backward propagation approach based on HYSPLIT trajectories. Low pollution was often observed for air masses from the north-west (behind cold fronts), and high pollution was observed from the southern areas such as industrialized Wu'an. The contribution of regional transport for the pollutants measured at the site during the observation period was estimated to be about 20 % to 30 % for trace gases and about 50 % for aerosols. In addition, agricultural burning events impacted the day-to-day variations in HCHO, CHOCHO and aerosols. It needs to be noted that although several MAX-DOAS measurements of trace gases and aerosols in the NCP area have been reported in previous studies, this study is the first work to derive a comprehensive set of vertical profiles of NO2, SO2, HONO, HCHO, CHOCHO and aerosols from measurements of one MAX-DOAS instrument. Also, so far, the validation of MAX-DOAS profile results by comparison with various surface in situ measurements as well as profile measurements from lidar and aircraft is scarce. Moreover, the backward propagation approach for characterizing the contributions of regional transport of pollutants from different regions was applied to the MAX-DOAS results of trace gases and aerosols for the first time.

MAX-DOAS measurements of tropospheric NO<sub>2</sub> and HCHO in Nanjing and a comparison to ozone monitoring instrument observations

“…Satellite-based remote sensing measurements provide indispensable spatial information on air pollutants (Burrows et al, 1999;Bovensmann et al, 1999;Callies et al, 2000;Levelt et al, 2006). Trace gas columns are derived from the satellite observations of Earth's reflected solar spectrum for the investigation of atmospheric dynamics and emissions from both anthropogenic and natural sources (Beirle et al, 2003(Beirle et al, , 2004Wenig et al, 2003;Richter et al, 2005;Zhang et al, 2007;van der A et al, 2008). Satellite measurements can also be used to determine the effectiveness of emission control measures (Mijling et al, 2009;Witte et al, 2009;Wu et al, 2013;Chan et al, 2015).…”

Measuring the Vertical Profiles of Aerosol Extinction in the Lower Troposphere by MAX-DOAS at a Rural Site in the North China Plain

“…The O 4 dSCDs were retrieved by the configured parameters, involving the fitting window (338-370 nm), the cross sections of nitrogen dioxide (NO 2 , 294K, 220K), ozone (O 3 , 223K, 243K), O 4 (293K), formaldehyde (HCHO, 298K), bromine oxide (BrO, 228K), water (H 2 O, 293K), nitrous acid (HONO, 296K) and two Ring spectra, as well as polynomial degree (5 order) and intensity offset (polynomial of order 1). In the process of data quality control, we rejected the O 4 dSCDs when the root mean square (RMS) of spectral fitting residual was bigger than 0.003, based on previous studies [50]. Figure 2 shows an example of DOAS fitting of O 4 , indicating that the O 4 absorption structure can be extracted from measured spectra and fitted well.…”

“…For each measured spectrum a wavelength calibration is performed before spectral fitting. The setting of DOAS retrieval parameters can be referred to previous studies [50]. The O 4 dSCDs were retrieved by the configured parameters, involving the fitting window (338-370 nm), the cross sections of nitrogen dioxide (NO 2 , 294K, 220K), ozone (O 3 , 223K, 243K), O 4 (293K), formaldehyde (HCHO, 298K), bromine oxide (BrO, 228K), water (H 2 O, 293K), nitrous acid (HONO, 296K) and two Ring spectra, as well as polynomial degree (5 order) and intensity offset (polynomial of order 1).…”

“…AE profiles retrieved from MAX-DOAS measurements in northern NCP showed that most of aerosols were confined below 1 km with an exponential decay with height, and sometimes the AE peak in the profile appeared at 300 m altitude [49]. Recent MAX-DOAS observations in the central western NCP showed that high AEs are mainly located below 1.4 km altitude with frequent lifted layers, and induced by complex factors, such as regional transport [50]. However, the knowledge of AE profile in the NCP is still incomplete, and the comparisons of AE profile between MAX-DOAS inversion and other measurement are also sparse.…”

Measurement Report: Aircraft Observations of Ozone, Nitrogen Oxides, and Volatile Organic Compounds over Hebei Province, China

“…The Atmosphere-Aerosol-Boundary Layer-Cloud (A 2 BC) Interaction Joint Experiment campaign collected meteorological, aerosol, and trace gas information from a ground-based site in Xingtai (114.36°E, 37.18°N, 182 m ASL) from May to December 2016 (Wang et al, 2018b(Wang et al, , 2019). An intensive observation period in May and June 2016 was conducted to coincide with ARIAs.…”