Sharp decreases in particulate matter concentrations during major events illustrate
that temporary emission control is an important influence on air quality improvement
during major events, especially for the APEC summit and the Grand Military Parade.
The two events are held in the fall season, when heavy pollution is becoming more
frequent. Surface observations and model sensitivity studies have revealed that the
emission control strategy is more effective at reducing SNA concentrations, and
traffic control has more than a 10% influence on the decrease in the PM 2.5 concentration. These findings indicate that China should continue to take aggressive steps
toward reducing SNA precursor emissions (especially NO x and NH 3 ) to effectively
reduce particulate matter concentrations.
6.5 Summary and Outlook
Based on observations and model studies, it can be concluded that changes in the
emissions of NO x and NH 3 have great impacts on aerosol Nr and PM 2.5 concentrations. More attention should be paid to NH 3 emission mitigation to achieve much
lower PM 2.5 concentrations in China, considering that NH 3 is the most important
alkaline gas in the atmosphere to neutralize acidic species forming secondary aerosols, especially NO 3
À .
In recent years, NO x emission abatement may contribute to the reduction of PM 2.5
concentrations, but the increase in NH 3 may offset the effectiveness of the decrease
in PM 2.5 that was gained from NO x emission reduction. However, the limited
availability of NH 3 measurements is currently a barrier to understanding the vital
role of NH 3 in secondary aerosol formation during haze pollution events and prevents a full assessment of the atmospheric Nr deposition. For large-scale surveys of
NH 3 variability across China, starting in September 2015, Pan et al. (2018)
established an NH 3 monitoring network in China (AMoN-China) based on the
diffusive technique with monthly integrated measurements at 53 sites. The accurate
measurement of gaseous NH 3 is a challenge because of its basicity, adhesion, and
solubility in water. The in situ observation of atmospheric NH 3 is still far from
sufficient to establish a database at the national scale for the analysis of current
pollution, modeling, and prediction of aerosol Nr in China. Long-term observation
of NH 3 concentrations on the national scale across China is still highly needed.
The sources of NO x have been well characterized. However, NH 3 emission sources
are more diverse and less well understood. Although huge efforts have been made in
the identification of NH 3 sources, there are still considerable uncertainties in the source
attribution of atmospheric NH 3 . The establishment of an emission inventory enables us
to estimate the scopes of predominant anthropogenic sources in China. However,
many previous studies have employed emission factors (EF) specific to foreign
studies, which has introduced large uncertainty to the results. Although highresolution and detailed inventories are necessary for accurate estimation, the application of these inventories would be labor and time-consuming. The isotope mixing
model (IsoSources) uses stable isotope signatures (δ
15
N-NH 3 ) to estimate the contributions of emission sources to atmospheric NH 3 (Pan et al. 2016a). This method
6 Contribution of Atmospheric Reactive Nitrogen to Haze Pollution in China
129
that temporary emission control is an important influence on air quality improvement
during major events, especially for the APEC summit and the Grand Military Parade.
The two events are held in the fall season, when heavy pollution is becoming more
frequent. Surface observations and model sensitivity studies have revealed that the
emission control strategy is more effective at reducing SNA concentrations, and
traffic control has more than a 10% influence on the decrease in the PM 2.5 concentration. These findings indicate that China should continue to take aggressive steps
toward reducing SNA precursor emissions (especially NO x and NH 3 ) to effectively
reduce particulate matter concentrations.
6.5 Summary and Outlook
Based on observations and model studies, it can be concluded that changes in the
emissions of NO x and NH 3 have great impacts on aerosol Nr and PM 2.5 concentrations. More attention should be paid to NH 3 emission mitigation to achieve much
lower PM 2.5 concentrations in China, considering that NH 3 is the most important
alkaline gas in the atmosphere to neutralize acidic species forming secondary aerosols, especially NO 3
À .
In recent years, NO x emission abatement may contribute to the reduction of PM 2.5
concentrations, but the increase in NH 3 may offset the effectiveness of the decrease
in PM 2.5 that was gained from NO x emission reduction. However, the limited
availability of NH 3 measurements is currently a barrier to understanding the vital
role of NH 3 in secondary aerosol formation during haze pollution events and prevents a full assessment of the atmospheric Nr deposition. For large-scale surveys of
NH 3 variability across China, starting in September 2015, Pan et al. (2018)
established an NH 3 monitoring network in China (AMoN-China) based on the
diffusive technique with monthly integrated measurements at 53 sites. The accurate
measurement of gaseous NH 3 is a challenge because of its basicity, adhesion, and
solubility in water. The in situ observation of atmospheric NH 3 is still far from
sufficient to establish a database at the national scale for the analysis of current
pollution, modeling, and prediction of aerosol Nr in China. Long-term observation
of NH 3 concentrations on the national scale across China is still highly needed.
The sources of NO x have been well characterized. However, NH 3 emission sources
are more diverse and less well understood. Although huge efforts have been made in
the identification of NH 3 sources, there are still considerable uncertainties in the source
attribution of atmospheric NH 3 . The establishment of an emission inventory enables us
to estimate the scopes of predominant anthropogenic sources in China. However,
many previous studies have employed emission factors (EF) specific to foreign
studies, which has introduced large uncertainty to the results. Although highresolution and detailed inventories are necessary for accurate estimation, the application of these inventories would be labor and time-consuming. The isotope mixing
model (IsoSources) uses stable isotope signatures (δ
15
N-NH 3 ) to estimate the contributions of emission sources to atmospheric NH 3 (Pan et al. 2016a). This method
6 Contribution of Atmospheric Reactive Nitrogen to Haze Pollution in China
129