Useful hourly measurements of formaldehyde at PAMS sites in New York

Hourly measurements of HCHO were carried out over a period of 2–3 years, at two New York sites (New York Botanical Gardens (NYBG) and Flax Pond) using Picarro cavity ring-down spectroscopy instruments, model G2307. HCHO data was corrected for the baseline drift by sampling zero air for 10 min on an hourly basis. The zero corrected HCHO data were then compared to collocated HCHO data from 2,4-dinitrophenylhydrazine (DNPH) cartridge samples. The difference averaged on a quarterly basis was used to adjust for the Picarro instrumental bias. The corrected Picarro data were found to agree well with collocated measurements from an Aerodyne Tunable Infrared Laser Direct Absorption Spectroscopy (TILDAS) instrument. HCHO showed a pronounced diel pattern in summer, with peak concentrations of 3.4–3.9 parts per billion by volume (ppbv), around noon to early afternoon, and a minimum of 1.4–1.9 ppbv, around 4–5 a.m. A strong seasonal gradient was observed with mean summer concentrations a factor of 2–3 higher than in winter, indicating the importance of secondary production. HCHO concentrations simulated by the Community Multiscale Air Quality model were lower than observed at NYBG, indicating that the emissions of HCHO and biogenic isoprene may be too low in urban areas. At Flax Pond modeled HCHO values were generally closer to observed concentrations except for April and May when modeled values were lower. The Picarro G2307 has the potential to provide accurate high temporal resolution HCHO data in the sub ppbv range, which is useful for model evaluation provided it is corrected for baseline drift and instrumental bias.