Increase of ambient formaldehyde in Beijing and its implication for VOC reactivity

Influencing atmospheric OH radical budget and tropospheric ozone production, ambient formaldehyde (HCHO) is one of the key oxygenated volatile organic compounds (OVOCs). We present the variations on formaldehyde column densities in summertime in Beijing retrieved from ozone monitoring instrument (OMI) between 2005 and 2011. Satellite columns of HCHO correlated well with available ground-based measurements despite some noticeable differences. The orthogonal distance regression (ODR) method was used to estimate the ratio between satellite columns and ground-level concentrations, whereas ordinary least squares (OLS) method was used to fit the trend of ambient formaldehyde. The formaldehyde concentrations derived from HCHO columns were in the range of 7–12 ppbv and steadily increased at an approximate rate of 0.64 ppbv/yr (7.8% at 2005 level) with an uncertainty of 51%. VOC reactivity quantified by means of OH loss rates showed increasing contribution from formaldehyde and acetaldehyde, rising from 35% in 2005 to 40% in 2010, and decreasing contribution from anthropogenic VOCs, dropping from 49% in 2005 to 40% in 2010. More attention should be paid to understanding the net feedback of increasing formaldehyde to ozone formation potential.