Ground-based measurements of atmospheric NH3 by Fourier transform infrared spectrometry at Hefei and comparisons with IASI data. (15th October 2022) - Wang, Wei
Abstract: Atmospheric ammonia (NH3 ) plays an important role in the formation of fine particulate matter, leading to severe environmental degradation and human health issues. In this work, ground-based Fourier transform infrared spectrometry (FTIR) observations are used to obtain the total columns of atmospheric NH3 at Hefei, China, from December 2016 to December 2020. After the presentation of the retrieval algorithm and uncertainty budget, we perform a spatio-temporal analysis of the dataset. Over the four years, NH3 columns have been increasing by 15.82% (2017–2018), 3.83% (2018–2019) and 3.68% (2019–2020). A clear seasonal cycle is observed, with the largest surface concentrations (12.93 ± 6.40 ppb) observed in June to August, and the lowest (4.08 ± 2.66 ppb) in November to January. The diurnal cycles of NH3 exhibit increased morning and afternoon concentrations. Interpretation of the diurnal cycles is difficult, however, the absence of a peak during rush hours, and the absence of correlation with CO and NO2 suggest that agriculture and not traffic is the main source of NH3 at Hefei. The polar plots of NH3 columns with wind and back trajectories of air masses calculated by the HYSPLIT model confirmed that agriculture was the dominant source of ammonia in four seasons, while urban anthropogenic emissions contributed to the high level of NH3 in summer over the Hefei site. We end this paper with a short validation exercise of NH3 columns retrieved from measurements of the IASI satellite data with the FTIR measurements over Hefei. Correlation coefficients (R) between the two datasets are 0.79 and 0.75 for IASI-A and IASI-B, with the slope of 0.96 and 1.10, respectively. The mean difference is −3.44 × 10 15 and −3.96 × 10 15 molec cm −2, with standard deviation of 7.16 × 10 15 and 8.10 × 10 15 molec cm −2, respectively. These results demonstrate the IASI and FTIR data, over Hefei, are in broad agreement. Graphical abstract: In order to know about the temporal and spatial distribution of atmospheric ammonia, and what influence ammonia columns over Hefei, China, we observed the total columns of atmospheric ammonia by ground-based FTIR remote sensing from December 2016 to December 2020. The time series of the ammonia column observed at the Hefei site are plotted. The green dots are the individual measurements of NH3 ; the red diamonds represent the daily averaged NH3 ; the blue line is the fitting curve of the individual NH3 columns. We discussed the seasonal trend, annual variability, diurnal variation of NH3, and the main factors that influence gaseous NH3 concentrations in Hefei. Image 1 Highlights: FTIR measurements of NH3 column and comparison with satellite data are reported. FTIR observations captured the spatio-temporal variation of NH3 columns. Agriculture was the dominant source of ammonia in four seasons over Hefei. IASI satellite data are in broad agreement with FTIR data over Hefei.