Determination of PM1 Sources at a Prague Background Site during the 2012–2013 Period Using PMF Analysis of Combined Aerosol Mass Spectra

Two intensive measurement campaigns using a compact time-of-flight aerosol mass spectrometer were carried out at the suburban site in Prague (Czech Republic) in summer (2012) and winter (2013). The aim was to determine the aerosol sources of the NR-PM1 fraction by PMF analysis of organic (OA) and inorganic aerosol mass spectra. Firstly, an analysis of the OA mass spectra was performed. Hydrocarbon-like OA (HOA), biomass burning OA (BBOA), and two types of oxygenated OA (OOA1) and (OOA2) were identified in summer. In winter, HOA, BBOA, long-range oxygenated OA (LROOA), and local oxygenated OA (LOOA) were determined. The identified HOA and BBOA factors were then used as additional input for the subsequent ME-2 analysis of the combined organic and inorganic spectra. This analysis resulted in six factors in both seasons. All of the previously reported organic factors were reidentified and expanded with the inorganic part of the spectra in both seasons. Two predominantly inorganic factors ammonium sulphate (AMOS) and ammonium nitrate (AMON) were newly identified in both seasons. Despite very similar organic parts of the mass profiles, the daily cycles of HOA and LOOA differed significantly in winter. It appears that the addition of the inorganic part of the mass profile, in some cases, reduces the ability of the model to identify physically meaningful factors.

Modelling changes in secondary inorganic aerosol formation and nitrogen deposition in Europe from 2005 to 2030

Secondary inorganic PM2.5 particles are formed from SOx, NOx and ammonia emissions, through the formation of either ammonium sulphate or ammonium nitrate. EU limits and WHO guidelines for PM2.5 levels are frequently exceeded in Europe, in particular in the winter months. In addition the critical loads for eutrophication are exceeded in most of the European continent. Further reductions in ammonia emissions and other PM precursors beyond the 2030 requirements could alleviate some of the health burden from fine particles, and also reduce the deposition of nitrogen to vulnerable ecosystems. Using the regional scale EMEP/MSC-W model, we have studied the effects of year 2030 ammonia emissions on PM2.5 concentrations and depositions of nitrogen in Europe in the light of present (2017) and past (2005) conditions. Our calculations show that in Europe the formation of PM2.5 from ammonia to a large extent is limited by the ratio between the emissions of ammonia on one hand, and SOx plus NOx, on the other hand. As the ratio of ammonia to SOx and NOx is increasing, the potential to further curb PM2.5 levels through reductions in ammonia emissions is decreasing. Here we show that per gram of ammonia emissions mitigated, the resulting reductions in PM2.5 levels simulated using 2030 emissions are about a factor of 2.6 lower than when 2005 emissions are used. However, this ratio is lower in winter, thus further reductions in the ammonia emissions in winter may have similar potentials as SOx and NOx in curbing PM2.5 levels in this season. Following the expected reductions of ammonia emission, depositions of reduced nitrogen should also decrease in Europe. However, as the reductions in NOx emission are larger than for ammonia, the fraction of total nitrogen (reduced plus oxidised nitrogen) deposited as reduced nitrogen is increasing and may exceed 60 % in most of Europe by 2030. Thus the potential for future reductions in the exceedances of critical loads for eutrophication in Europe will mainly rely on the ability to reduce ammonia emissions.

Atmospheric Measurements at the Foot and the Summit of Mt. Tai – Part II: HONO Budget and Radical (RO_x + NO₃) Chemistry in the Lower Boundary Layer

In the summer of 2018, a comprehensive field campaign, with measurements on HONO and related parameters, was conducted at the foot (150 m a.s.l.) and the summit of Mt. Tai (1534 m a.s.l.) in the central North China Plain (NCP). With the implementation of a 0-D box model, the HONO budget with six additional sources and its role in radical chemistry at the foot station were explored. We found that the model default source, NO + OH, could only reproduce the observed HONO by 13 %, leading to a strong unknown source strength up to 3 ppbv h−1. Among the additional sources, the NO2 uptake on the ground surface dominated (~70 %) night-time HONO formation, and its photo-enhanced reaction dominated (~80 %) daytime HONO formation. Their contributions were sensitive to the mixing layer height (MLH) used for the parameterizations, highlighting the importance of a reasonable MLH for exploring ground-level HONO formation in 0-D models and the necessity of gradient measurements. A HONO / NOx ratio of 0.7 % for the direct emission was inferred and a new method to quantify its contribution to the observations was proposed and discussed. Aerosol-derived sources, including the NO2 uptake on the aerosol surface and the particulate nitrate photolysis, did not lead to significant HONO formation, with their contributions lower than NO + OH. HONO photolysis in the early morning initialized the daytime photochemistry at both the foot and the summit stations and also was a substantial radical source throughout the daytime, with contributions higher than or about one-quarter of O3 photolysis to OH initiation at the foot and the summit stations, respectively. Moreover, we found that OH dominated the atmospheric oxidizing capacity in the daytime, while NO3 appeared to be significant at night. Peaks of NO3 time series and diurnal variation reached 22 and 9 pptv, respectively. NO3 induced reactions contribute 18 % of nitrate formation potential (P(HNO3)) and 11 % of the isoprene (C5H8) oxidation throughout the whole day. At night, NO3 chemistry led to 51 % or 44 % of P(HNO3) or the C5H8 oxidation, respectively. NO3 chemistry may significantly affect night-time secondary organic and inorganic aerosol formation in this high-O3 region, implying that NO3 chemistry could significantly affect night-time secondary organic and inorganic aerosol formation in this high-O3 region. Considering the severe O3 pollution in the NCP and the very limited NO3 measurements, we suggest that besides direct measurements of HOx and primary HOx precursors (O3, HONO, alkenes, etc.), NO3 measurements should be conducted to understand the atmospheric oxidizing capacity and air pollution formation in this and similar regions.