Influence of Ammonia and Relative Humidity on the Formation and Composition of Secondary Brown Carbon from Oxidation of 1-Methylnaphthalene and Longifolene

Abstract

Improved understanding of the optical properties of secondary organic aerosol (SOA) particles is needed to better predict their climate impacts. Here, SOA was produced by reacting 1-methylnaphthalene or longifolene with hydroxyl radicals (OH) under variable ammonia (NH3), nitrogen oxide (NO x ), and relative humidity (RH) conditions. In the presence of NH3 and NO x , longifolene-derived aerosols had relatively high single scattering albedo (SSA) values and low absorption coefficients at 375 nm independent of RH, suggesting that the longifolene SOA is mostly scattering. In 1-methylnaphthalene experiments, the resulting SSA and SOA mass absorption coefficient (MACorg) values suggest the formation of light-absorbing SOA, and the addition of high NO x and high NH3 enhanced the SOA absorption. Under intermediate-NO x dry conditions, the MACorg values increased from 0.13 m2 g–1 in NH3-free conditions to 0.28 m2 g–1 in high-NH3 conditions. Under high-NH3 conditions, the MACorg value further increased to 0.36 m2 g–1 with an increase in RH. Under dry high-NO x conditions, the MACorg value increased from 0.42 to 0.67 m2 g–1 with the addition of NH3, while with elevated RH, the MACorg value reached 0.70 m2 g–1. The time series of MACorg showed increasing trends only in the presence of NH3. Composition analysis of SOA suggests that organonitrates, nitroorganics, and other nitrogen-containing organic compounds (NOCs) are potential chromophores in the 1-methylnaphthalene SOA. Significant formation of NOCs was observed in the presence of high-NO x and NH3 and was enhanced under elevated RH.

Chemical Structure Regulates the Formation of Secondary Organic Aerosol and Brown Carbon in Nitrate Radical Oxidation of Pyrroles and Methylpyrroles

“…In addition, size-resolved mass distributions and particle chemical composition were measured in real-time using a mini aerosol mass spectrometer (mAMS) coupled with a compact time-of-flight mass spectrometer (Aerodyne Research, Inc.) . The size-resolved aerosol mass distribution was compared with the concurrent SEMS-derived aerosol volume distribution to determine the effective aerosol density (ρ eff ). − The calculation of ρ eff is described in the SI, Text S2. The calculated ρ eff was then used to estimate the SOA mass concentrations shown in Table .…”

“…The single scattering albedo (SSA) at 375 nm was calculated by The calculated SSA is size-dependent and is calculated as a function of the size parameter (α). α was determined with the following equation using d m , and the wavelength of radiation used in PAX is λ = 375 nm: Offline <MAC> profiles were obtained using measurements from a UV–vis spectrophotometer (Beckman DU-640). All the UV–vis spectroscopy measurements were operated under 293 K and 1 atm .…”

Effect of relative humidity, NOx, and ammonia on the physical properties of naphthalene secondary organic aerosols

“…Liu et al 43 observed the formation of nitrogen-containing organics and an increase in the absorption coefficient during exposure of a low-NO x toluene SOA to ammonia. Cui et al 20 observed an enhancement in the absorption coefficient of a 1-methylnaphthalene SOA in the presence of NH 3 , especially under humidified conditions. Extensive studies have been conducted exploring the mechanism of NH 3 -driven browning reactions.…”

Nitrogen-Containing Compounds Enhance Light Absorption of Aromatic-Derived Brown Carbon

“…Recent studies have shown the significance of aromatics in the formation of light-absorbing SOA. − Aromatic-derived BrC with a global production of 4.1 TgC yr –1 can dominate secondary BrC formation . Among these aromatics, ethylbenzene is one of the most abundant compounds, with the global annual emission rate following those of benzene and toluene .…”