Investigating the Sources of Formaldehyde and Corresponding Photochemical Indications at a Suburb Site in Shanghai From MAX‐DOAS Measurements

Multi‐AXis‐Differential Optical Absorption Spectroscopy (MAX‐DOAS) measurements were performed to obtain vertical distributions of nitrogen dioxide (NO 2 ), formaldehyde (HCHO) and glyoxal (CHOCHO) from October 17 to November 21, 2019 in Qingpu, a suburb of Shanghai, China. The consistencies of MAX‐DOAS and other independent observations of HCHO and NO 2 verified the effectiveness of the inversion results. The secondary formation was identified as the predominant HCHO sources (57.4% of all) by a statistical regression analysis of HCHO with carbon monoxide (CO) and CHOCHO. The photochemical indications of HCHO were investigated through the ratios of HCHO to CHOCHO ( R GF ) and NO 2 ( R FN ). The results showed that anthropogenic influence on R GF mainly existed in the layer of 0–800 m. The dependences of anthropogenic emission on R GF were negative in 0–200 m layer and positive in 200–800 m layer when NO 2 level was higher than 5 ppbv. The sensitivity analysis of O 3 formation in 0–2 km layer was concluded as follows: between 9:00 and 11:00 LT, the O 3 formation was controlled by VOC‐limited regime alone; while it turned into transition regime in 1.7–2 km layer from 11:00 to 13:00 LT; then the transition regime moved down to the layer of 1.3–1.4 km from 13:00 to 15:00 LT and the NO x ‐limited regime began to occur in 1.4–2.0 km layer.