Researchers have questioned the explanation of nitrous acid under the assumption of photostability and re evaluated the sources and dynamics of HONO in urban atmosphere through a combination of field observations and chemical chamber model simulations. The study used mid infrared quantum cascade laser absorption spectroscopy technology to conduct on-site observations at high altitudes in Houston city, accurately measuring the concentrations of key species such as HONO and NO ₂. By constructing a chemical box model, the photochemical reactions of vehicle exhaust from emission to dilution were simulated, with a focus on analyzing the dynamic changes of HONO in non-equilibrium states. The study further used the model to simulate the nighttime NO ₓ chemical system, and quantitatively analyzed the source of nighttime HONO by setting different scenarios (pure chemistry, chemistry+deposition, chemistry+deposition+emission).

The research results indicate that: (1) HONO often does not reach a photostable in the urban atmosphere, and the observed negative growth rate is mainly due to sampling of fresh pollutants that have not undergone sufficient photochemical aging, rather than unknown secondary sources that must exist; (2) The increase in the daytime HONO/NO ₓ ratio can be reasonably explained by known homogeneous chemical reactions (NO+OH) and pollutant mixing processes, without the need to introduce additional optical driving sources; (3) The accumulation of HONO at night is the result of the combined action of NO ₓ oxidation chemistry, direct emissions, and dry deposition. The model estimates that its heterogeneous generation efficiency is about 1 HONO molecule produced per hour for every 15 NO ₂ molecules deposited.

The core equipment used for on-site observations in the above study was a dual channel tunable infrared quantum cascade laser absorption spectrometer, which was conducted at the top of the Moody Tower, located 70 meters high on the campus of the University of Houston. The essence of this method lies in its high specificity, high temporal resolution, and the absence of chemical derivatization or liquid-phase extraction of the sample, thereby minimizing sampling errors to the greatest extent possible.

The Aerodyne viscous gas monitoring system, represented by an Australian company, can achieve direct and rapid measurement of various viscous gas molecules (such as HONO, NH3, etc.). The technical advantages of this product are as follows:

Active passivation systemImprove the response time of viscous molecules with minimal loss for high-frequency 10Hz measurements.

Realize synchronous measurement of nitrogen-containing gasesHONO and NH3, as viscous gas molecules, play important roles in photocatalytic oxidation and air pollution. HONO is a powerful photodegradation source of OH radicals, involving interactions between multiple layers of soil and atmosphere, and has strong interdisciplinary characteristics, opening up new horizons for global nitrogen cycle research.

The measurement accuracy is ppt levelHelps to improve the parameterization scheme of HONO generation and consumption process in the model, thereby more accurately simulating the formation process of pollutants such as ozone and secondary particulate matter, and enhancing the ability to predict air quality and evaluate climate effects.