What controls aerosol 815N-NO3-? NOx emission sources vs. nitrogen isotope fractionation

Atmospheric 815N-NO3- has been used to reveal NOx (NO + NO2) sources as NO3- is the ultimate sink of NOx. How-ever, it remains questionable whether the nitrogen isotope fractionation among NOy (NO, NO2, NO3, N2O5, HNO3 , NO3-) engender the misjudgment of NOx emission sources by affecting 815N-NOy. To explore this issue, we inte-grated the dataset of aerosol 815N-NO3- values and ratios of fNO2 (fNO2 = NO2/(NO2 + NO)), calculated the nitrogen isotope fractionation factors (As) among NOy, compared the total energy consumption in Beijing-Tianjin-Hebei region (BTH) from 2013 to 2018. Results showed that, although the total energy consumption structure changed from 2013 to 2018 in BTH, there were fewer interannual variances of aerosol 815N-NO3- values. Nitrogen isotope fractionation fac-tors between NO and NO2 (A0), NO2 and NO3 (A2), NO2 and N2O5 (A3), NO2 and ClONO2 (A4) also displayed less in-terannual variations from 2013 to 2018 in BTH. But both aerosol 815N-NO3- and As displayed significant seasonal patterns , there was significant relationship between monthly aerosol 815N-NO3- and As, which suggested that As have important influence on shaping aerosol 815N-NO3- and further discriminating NOx emission sources. This study implies that we should refine the As when employing atmospheric 815N-NO3-to quantify NOx source allocation.

Automated summary

The isotopic fractionation among NOy species can affect the evaluation of NOx sources. This study integrated aerosol 815N-NO3- data and fNO2 ratios to investigate the nitrogen isotope fractionation factors (As) in the Beijing-Tianjin-Hebei region from 2013 to 2018. The results showed significant seasonal patterns in both aerosol 815N-NO3- and As, emphasizing the importance of considering As when using atmospheric 815N-NO3- to quantify NOx source allocation.