Temporal Variation of NO2 and HCHO Vertical Profiles Derived from MAX-DOAS Observation in Summer at a Rural Site of the North China Plain and Ozone Production in Relation to HCHO/NO2 Ratio

Abstract

We performed a comprehensive and intensive field experiment including ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurement at Raoyang (115°44′ E, 38°14′ N; 20 m altitude) in summer (13 June–20 August) 2014. The NO2 and HCHO profiles retrieved by MAX-DOAS take on different vertical distribution shapes, with the former declining with the increasing altitude and the latter having an elevated layer. The average levels of vertical column densities (VCDs) and near-surface volume mixing ratios (VMRs) were 1.02 ± 0.51 × 1016 molec·cm−2 and 3.23 ± 2.70 ppb for NO2 and 2.32 ± 0.56 × 1016 molec·cm−2 and 5.62 ± 2.11 ppb for HCHO, respectively. The NO2 and HCHO levels are closely connected with meteorological conditions, with the larger NO2 VCDs being associated with lower temperature, higher relative humidity (RH) and lower planetary boundary layer height (PBLH). With respect to the diurnal variations of vertical distribution, the NO2 in the residual layer gradually disappeared from 1.2 km height to the surface during the period of 7:00–11:00 Beijing time (BJ), and the near-surface NO2 had larger VMRs in the early morning and evening than in the later morning and afternoon. An elevated HCHO layer was observed to occur persistently with the lifted layer height rising from ~0.5 km to ~1.0 km before 10:00 BJ; the near-surface HCHO VMRs gradually increased and peaked around 10:00 BJ. The ratios of HCHO to NO2 (RHCHO-NO2) were generally larger than two in the boundary layer from 11:00 BJ until 19:00 BJ, the time period when ozone photochemistry was most active. Thus, ozone (O3) production was mainly in the NOx-limited regime during the observation campaign, which was closely related to relatively high temperatures and low RH. The O3 production regimes also changed with the wind’s direction. These results are significant to reveal the formation mechanism of O3 pollution and develop strategies for controlling the O3 photochemical pollution over the North China Plain.

MAX-DOAS Measurements of Tropospheric NO2 and HCHO Vertical Profiles at the Longfengshan Regional Background Station in Northeastern China

“…The fitting parameters for NO 2 and HCHO spectral analyses were similar as in previous studies [ 36 , 45 , 46 ], see Table 1 . In this study, in order to improve the credibility of the data, only the spectra with root mean square (RMS) of the spectral fitting residuals < 0.003 and solar zenith angle (SZA) < 75° were retained [ 46 , 47 ]. Under the control of these two thresholds, we retained 70.67% of the NO 2 profiles and 68.77% of the HCHO profiles.…”

“…The vertical profiles of NO 2 and HCHO VMRs in the lower troposphere (0~4 km) were retrieved from the dSCDs by using the Profile inversion algorithm of aerosol extinction and the trace gas concentration algorithm (PriAM) [ 47 ]. The inversion consists of two procedures.…”

“…In the first step, the vertical profiles of aerosol extinction (AE) were retrieved from the measured O 4 dSCDs. Then the retrieved AE profiles were used for the inversion of the trace gas profiles [ 45 , 47 ]. For HCHO, the AE profiles at 360 nm were transformed into profiles at 343 nm by using the Ångström exponent.…”

“…The inversion parameters of surface albedo, single scattering albedo, and asymmetry factor were listed in Table 2. The PriAM algorithm was based on the optimal estimation method to obtain the vertical profiles via loop iteration, which minimized the parameter of cost function [47,52]. The smaller values of the cost function correspond to the more reliable retrieval results.…”