Sources And Transformation Of HONO,Particulate Nitrite And Nitro-phenols In Typical Areas In North China

Nitrous acid and nitro-phenols are two kinds of important nitrogen containing trace species in the atmosphere. Photolysis of HONO serves as one of the major sources of OH radicals. However, unknown source of HONO existed and further understanding of transformations between HONO and nitrite is needed. Nitro-phenols are of potential sources of HONO which are products and tracers of biomass burning.They are also major components of Brown Carbon, which are toxic and could bring harm to plants, hydro bios, and human being. Researches have shown severe particulate matter pollution and high levels of particulate nitrite observed in North China. Therefore, we conducted field measurements in typical sites of North China in typical seasons. Not only did we studied the pollution characteristics, sources and transformations of HONO and particulate nitrite, but also discussed temporal varations, sources and contributions of nitro-phenols.To understand the pollution characteristics of HONO and particulate nitrite, MARGA was deployed in the field campaign in urban Ji’nan. During the observation period, the average concentration of HONO was 0.35 ppbv, characterized by higher concentrations at night than in the daytime and a peak in the early morning. And high concentrations of HONO were observed during the periods with low wind speed. Besides, good correlations between HONO and NOx were found in pollution episodes with vehicles exhaust plumes. The emission factor of HONO in winter in Ji’nan is HONO/NOx=0.58%. Additionally, heterogeneous reactions of NO2 is another major source of HONO which contributed about half of high concentrations of HONO. The conversion rate cHONO* ranged from 0.05% to 0.96% h-1, which rose with the raise of aerosols surface area and the amount of water. During the field measurements in winter in Ji’nan, high concentrations of particulate nitrite were observed, with an average concentration of 2.08 μg m-3. Fine particulate nitrite exhibited similar diurnal variations with HONO, but delayed in the time when the peak and the valley appeared. Correlation analysis indicates that the majority of the produced nitrous acid existed in particles instead of gas phase due to high concentrations of ammonia and ammonium ions. Furthermore, particulate nitrite is a potential source of HONO which could be converted into HONO when the temperature is high, RH is high and aerosol is acidic.We collected PM2.5 samples at an urban site of Ji’nan, rural sites of Yucheng and Baoding, and a mountain site of Mt. Tai in typical seasons and nitro-phenols were then identified and quantified using HPLC-MS. During the measurements, nitro-phenols exhibited apparent seasonal variations, daily variations and differences between different sites. The average concentrations of nitro-phenols in winter in Ji’nan, and in summer in Ji’nan, Yucheng, and Mt. Tai were 48.4 ng m-3,9.8 ng m-3, 5.7 ng m-3,5.9 ng m-3, and 2.5 ng m-3, respectively. Besides, PMF was utilized and five possible major sources were identified. The sources were urban plume, coal combustion, biomass burning, secondary formation, and aged coal combustion plume. Among them, coal burning contributed significantly to nitro-phenols in the city sites, especially during the winter. In summer, all the four sites were influenced by biomass burning. In rural areas and mountain sites, however, secondary formation is the major source of nitro-phenols and the processes were controlled by the concentrations of NOx and atmospheric oxidants.In this study, we revealed that particulate nitrite is the major product of heterogeneous reactions of NO2 instead of HONO. In the daytime, particulate nitrite could be converted into HONO an thus serves as its potential source. Besides, we measured the concentration of nitro-phenols in four sites in North China and studied the contributions of coal burning, biomass burning and secondary formation processes. These conclusions could not only be useful to further studies on the transformation mechanism of HONO, nitrite and of nitro-phenols, but also give supports to atmospheric model studies and regional pollution treatment.