A critical evaluation of proxy methods used to estimate the acidity of atmospheric particles

Hennigan, C. J.; Izumi, J.; Sullivan, A. P.; Weber, R. J.; Nenes, A.

doi:10.5194/acp-15-2775-2015

Articles | Volume 15, issue 5

https://doi.org/10.5194/acp-15-2775-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-15-2775-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 15, issue 5

Research article

|

10 Mar 2015

Research article |

| 10 Mar 2015

A critical evaluation of proxy methods used to estimate the acidity of atmospheric particles

C. J. Hennigan, J. Izumi, A. P. Sullivan, R. J. Weber, and A. Nenes

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Views and downloads (calculated since 05 Nov 2014)

Month	HTML	PDF	XML	Total
Nov 2014	230	180	22	432
Dec 2014	77	58	43	178
Jan 2015	63	24	30	117
Feb 2015	23	14	2	39
Mar 2015	185	157	10	352
Apr 2015	74	79	2	155
May 2015	45	63	6	114
Jun 2015	44	58	2	104
Jul 2015	42	66	2	110
Aug 2015	36	58	1	95
Sep 2015	22	64	1	87
Oct 2015	45	48	1	94
Nov 2015	47	55	5	107
Dec 2015	14	36	2	52
Jan 2016	59	45	5	109
Feb 2016	34	20	0	54
Mar 2016	34	30	0	64
Apr 2016	15	24	1	40
May 2016	17	19	0	36
Jun 2016	9	12	0	21
Jul 2016	16	21	2	39
Aug 2016	13	25	0	38
Sep 2016	17	36	0	53
Oct 2016	15	13	0	28
Nov 2016	13	6	1	20
Dec 2016	6	15	0	21
Jan 2017	24	31	1	56
Feb 2017	28	19	1	48
Mar 2017	35	26	2	63
Apr 2017	37	25	1	63
May 2017	30	37	1	68
Jun 2017	42	36	0	78
Jul 2017	33	27	0	60
Aug 2017	21	42	1	64
Sep 2017	23	44	0	67
Oct 2017	20	41	1	62
Nov 2017	15	36	0	51
Dec 2017	19	47	0	66
Jan 2018	14	47	0	61
Feb 2018	18	58	0	76
Mar 2018	24	53	0	77
Apr 2018	17	55	1	73
May 2018	27	92	1	120
Jun 2018	19	81	0	100
Jul 2018	26	61	2	89
Aug 2018	19	75	2	96
Sep 2018	19	40	3	62
Oct 2018	24	55	3	82
Nov 2018	19	37	1	57
Dec 2018	25	32	1	58
Jan 2019	20	40	1	61
Feb 2019	16	36	1	53
Mar 2019	8	44	0	52
Apr 2019	13	50	2	65
May 2019	18	51	0	69
Jun 2019	15	35	0	50
Jul 2019	21	43	0	64
Aug 2019	12	36	3	51
Sep 2019	6	58	0	64
Oct 2019	15	35	0	50
Nov 2019	17	48	0	65
Dec 2019	15	42	0	57
Jan 2020	15	38	0	53
Feb 2020	10	30	0	40
Mar 2020	15	34	0	49
Apr 2020	24	28	0	52
May 2020	14	19	0	33
Jun 2020	33	14	0	47
Jul 2020	27	35	4	66
Aug 2020	22	17	2	41
Sep 2020	20	12	0	32
Oct 2020	11	7	2	20
Nov 2020	18	11	1	30
Dec 2020	18	15	2	35
Jan 2021	23	17	0	40
Feb 2021	15	13	0	28
Mar 2021	23	16	2	41
Apr 2021	29	27	0	56
May 2021	18	27	2	47
Jun 2021	29	38	1	68
Jul 2021	35	33	0	68
Aug 2021	61	40	0	101
Sep 2021	34	27	0	61
Oct 2021	36	51	2	89
Nov 2021	40	48	0	88
Dec 2021	34	22	1	57
Jan 2022	35	17	0	52
Feb 2022	23	15	1	39
Mar 2022	38	15	1	54
Apr 2022	45	23	1	69
May 2022	27	18	0	45
Jun 2022	26	10	0	36
Jul 2022	32	20	0	52
Aug 2022	35	26	0	61
Sep 2022	32	17	1	50
Oct 2022	31	14	0	45
Nov 2022	65	27	0	92
Dec 2022	53	20	0	73
Jan 2023	46	29	1	76
Feb 2023	41	32	0	73
Mar 2023	43	37	0	80
Apr 2023	29	26	1	56
May 2023	48	24	0	72
Jun 2023	62	13	1	76
Jul 2023	73	20	0	93
Aug 2023	76	38	4	118
Sep 2023	109	23	2	134
Oct 2023	191	23	4	218
Nov 2023	228	16	3	247
Dec 2023	115	24	3	142
Jan 2024	95	26	0	121
Feb 2024	76	22	1	99
Mar 2024	120	33	1	154
Apr 2024	109	21	4	134
May 2024	96	37	4	137
Jun 2024	103	17	1	121
Jul 2024	53	20	2	75
Aug 2024	55	18	3	76
Sep 2024	32	31	0	63
Oct 2024	61	32	0	93
Nov 2024	37	26	3	66
Dec 2024	29	13	1	43
Jan 2025	43	29	0	72
Feb 2025	62	13	3	78
Mar 2025	70	23	2	95
Apr 2025	52	33	1	86
May 2025	72	19	1	92
Jun 2025	101	26	1	128
Jul 2025	81	17	1	99
Aug 2025	161	20	4	185
Sep 2025	110	22	1	133
Oct 2025	54	35	0	89
Nov 2025	19	14	0	33

Cumulative views and downloads (calculated since 05 Nov 2014)

Month	HTML	PDF	XML	Total
Nov 2014	230	180	22	432
Dec 2014	77	58	43	178
Jan 2015	63	24	30	117
Feb 2015	23	14	2	39
Mar 2015	185	157	10	352
Apr 2015	74	79	2	155
May 2015	45	63	6	114
Jun 2015	44	58	2	104
Jul 2015	42	66	2	110
Aug 2015	36	58	1	95
Sep 2015	22	64	1	87
Oct 2015	45	48	1	94
Nov 2015	47	55	5	107
Dec 2015	14	36	2	52
Jan 2016	59	45	5	109
Feb 2016	34	20	0	54
Mar 2016	34	30	0	64
Apr 2016	15	24	1	40
May 2016	17	19	0	36
Jun 2016	9	12	0	21
Jul 2016	16	21	2	39
Aug 2016	13	25	0	38
Sep 2016	17	36	0	53
Oct 2016	15	13	0	28
Nov 2016	13	6	1	20
Dec 2016	6	15	0	21
Jan 2017	24	31	1	56
Feb 2017	28	19	1	48
Mar 2017	35	26	2	63
Apr 2017	37	25	1	63
May 2017	30	37	1	68
Jun 2017	42	36	0	78
Jul 2017	33	27	0	60
Aug 2017	21	42	1	64
Sep 2017	23	44	0	67
Oct 2017	20	41	1	62
Nov 2017	15	36	0	51
Dec 2017	19	47	0	66
Jan 2018	14	47	0	61
Feb 2018	18	58	0	76
Mar 2018	24	53	0	77
Apr 2018	17	55	1	73
May 2018	27	92	1	120
Jun 2018	19	81	0	100
Jul 2018	26	61	2	89
Aug 2018	19	75	2	96
Sep 2018	19	40	3	62
Oct 2018	24	55	3	82
Nov 2018	19	37	1	57
Dec 2018	25	32	1	58
Jan 2019	20	40	1	61
Feb 2019	16	36	1	53
Mar 2019	8	44	0	52
Apr 2019	13	50	2	65
May 2019	18	51	0	69
Jun 2019	15	35	0	50
Jul 2019	21	43	0	64
Aug 2019	12	36	3	51
Sep 2019	6	58	0	64
Oct 2019	15	35	0	50
Nov 2019	17	48	0	65
Dec 2019	15	42	0	57
Jan 2020	15	38	0	53
Feb 2020	10	30	0	40
Mar 2020	15	34	0	49
Apr 2020	24	28	0	52
May 2020	14	19	0	33
Jun 2020	33	14	0	47
Jul 2020	27	35	4	66
Aug 2020	22	17	2	41
Sep 2020	20	12	0	32
Oct 2020	11	7	2	20
Nov 2020	18	11	1	30
Dec 2020	18	15	2	35
Jan 2021	23	17	0	40
Feb 2021	15	13	0	28
Mar 2021	23	16	2	41
Apr 2021	29	27	0	56
May 2021	18	27	2	47
Jun 2021	29	38	1	68
Jul 2021	35	33	0	68
Aug 2021	61	40	0	101
Sep 2021	34	27	0	61
Oct 2021	36	51	2	89
Nov 2021	40	48	0	88
Dec 2021	34	22	1	57
Jan 2022	35	17	0	52
Feb 2022	23	15	1	39
Mar 2022	38	15	1	54
Apr 2022	45	23	1	69
May 2022	27	18	0	45
Jun 2022	26	10	0	36
Jul 2022	32	20	0	52
Aug 2022	35	26	0	61
Sep 2022	32	17	1	50
Oct 2022	31	14	0	45
Nov 2022	65	27	0	92
Dec 2022	53	20	0	73
Jan 2023	46	29	1	76
Feb 2023	41	32	0	73
Mar 2023	43	37	0	80
Apr 2023	29	26	1	56
May 2023	48	24	0	72
Jun 2023	62	13	1	76
Jul 2023	73	20	0	93
Aug 2023	76	38	4	118
Sep 2023	109	23	2	134
Oct 2023	191	23	4	218
Nov 2023	228	16	3	247
Dec 2023	115	24	3	142
Jan 2024	95	26	0	121
Feb 2024	76	22	1	99
Mar 2024	120	33	1	154
Apr 2024	109	21	4	134
May 2024	96	37	4	137
Jun 2024	103	17	1	121
Jul 2024	53	20	2	75
Aug 2024	55	18	3	76
Sep 2024	32	31	0	63
Oct 2024	61	32	0	93
Nov 2024	37	26	3	66
Dec 2024	29	13	1	43
Jan 2025	43	29	0	72
Feb 2025	62	13	3	78
Mar 2025	70	23	2	95
Apr 2025	52	33	1	86
May 2025	72	19	1	92
Jun 2025	101	26	1	128
Jul 2025	81	17	1	99
Aug 2025	161	20	4	185
Sep 2025	110	22	1	133
Oct 2025	54	35	0	89
Nov 2025	19	14	0	33

Latest update: 08 Nov 2025

Short summary

We show that the ion balance and molar ratio methods are unsuitable for use as aerosol pH proxies. Our recommendation is that 1) thermodynamic equilibrium models constrained by both gas and aerosol inputs run in the forward (open) mode, and 2) the phase partitioning of ammonia provides the best predictions of aerosol pH. Given the significance of acidity for numerous chemical processes in the atmosphere, the implications of this study are important and far reaching.