Contribution of Nitrated Phenols to Wood Burning Brown Carbon Light Absorption in Detling, United Kingdom during Winter Time

We show for the first time quantitative online measurements of five nitrated phenol (NP) compounds in ambient air (nitrophenol C<sub>6</sub>H<sub>5</sub>NO<sub>3</sub>, methylnitrophenol C<sub>7</sub>H<sub>7</sub>NO<sub>3</sub>, nitrocatechol C<sub>6</sub>H<sub>5</sub>NO<sub>4</sub>, methylnitrocatechol C<sub>7</sub>H<sub>7</sub>NO<sub>4</sub>, and dinitrophenol C<sub>6</sub>H<sub>4</sub>N<sub>2</sub>O<sub>5</sub>) measured with a micro-orifice volatilization impactor (MOVI) high-resolution chemical ionization mass spectrometer in Detling, United Kingdom during January–February, 2012. NPs absorb radiation in the near-ultraviolet (UV) range of the electromagnetic spectrum and thus are potential components of poorly characterized light-absorbing organic matter (“brown carbon”) which can affect the climate and air quality. Total NP concentrations varied between less than 1 and 98 ng m<sup>–3</sup>, with a mean value of 20 ng m<sup>–3</sup>. We conclude that NPs measured in Detling have a significant contribution from biomass burning with an estimated emission factor of 0.2 ng (ppb CO)<sup>−1</sup>. Particle light absorption measurements by a seven-wavelength aethalometer in the near-UV (370 nm) and literature values of molecular absorption cross sections are used to estimate the contribution of NP to wood burning brown carbon UV light absorption. We show that these five NPs are potentially important contributors to absorption at 370 nm measured by an aethalometer and account for 4 ± 2% of UV light absorption by brown carbon. They can thus affect atmospheric radiative transfer and photochemistry and with that climate and air quality.